Category: insects

Readers’ wildlife photos

February 6, 2023 • 8:15 am

Today we have another photo-and-text biology story from Athayde Tonhasca Júnior. Today’s subject is insect sleep and nocturnal behavior.  Athayde’s narrative is indented, and you should click on the photos to enlarge them.

When the night has come and the land is dark

We humans spend between 25 to 35% of our lifespan sleeping. It’s a significant chunk of time in the land of Nod, so sleep must be vital. But surprisingly, doctors and scientists are not sure why we sleep so much – or at all, for that matter. A period of unconsciousness may be required so that our body can repair itself and restore some physiological or chemical functions; it could help us conserve energy, especially at night, when our ancestral search for food was less efficient.

Two girls on the stove bench. Art by Albert Anker, 1895. Wikimedia Commons:

Whatever the reason, we need our resting. And so do other animals, including insects. In the case of bees and wasps, females have the obvious option of a cosy nest to tuck into for the night. But males do not: they are not welcome back once they mature and leave the nest, so they are destined for a vagabond life. When the night comes and the temperature drops, they have to rough it by entering a state of torpor until the morning sun heats them up again.

Flowers are the bedding choice for males of many species: on a chilly morning, you may find sluggish bees curled up among petals. These sleeping arrangements offer some protection against roaming predators, are convenient spots for meeting females during daytime, and also make males of some species exceptional pollinators.

Night, night, sleep tight © Todd Esque, U.S. Geological Survey:

But protection doesn’t seem to be crucial, since many bees just sleep in the open. If you visit a garden during early morning or early evening, you may spot bumble bees slumbering on top of a flower, or even hanging upside-down from a blossom or under a leaf. Most of them are males, but the odd female may join them if she’s caught outside when temperature drops quickly at sunset. Watch a sleeping bee clinging to a plant and refusing to be woken up.

Sleeping bumble bees clinging to a Welsh onion (Allium fistulosum) inflorescence:

Some bees and wasps seem to deliberately make themselves uncomfortable for the night. They hang from the end of a twig, a dried flower head or a thin stem, clamped on with their mandibles. We don’t know why they sleep like this; perhaps to make them less visible to predators, who may mistake them for plant extensions.

A Nomada sp. cuckoo bee sleeping anchored by its mandibles © Giles Gonthier, Wikimedia Commons:

Male bees are not much into socialising: they tend to avoid each other, when not being downright aggressive. But after sunset, males of some species spend the night close together, forming clusters of bees clinging from branches or flowers. Not only that, these males tend to return again and again to the same spot every evening for their sleep. Gregarious sleeping seems like a dangerous life choice: such concentrations of lethargic bees must tempt many a predator. One possible explanation for this behaviour is the dilution effect: the larger the group of prey, the smaller the chance of any individual being the victim of a raider. Some fish, penguins and mammals that live in the open resort to this type of defence.

A long-horned bee (Melissodes sp.) slumber party © Todd Sonfileth, Oregon Public Broadcasting:

We don’t have much information about the consequences of sleeping in the open for male bees. But when you tuck in tonight, remember that a peaceful, uneventful kip is not a given for everybody.

When the night comes to an end in a Central American forest, its nocturnal denizens – bats, owls, rodents and cats – begin to retreat to their shelters. At this time, before the crack of dawn, light levels are up to 100 million times dimmer than during the day, so it’s still too dark for the day-shift inhabitants.

A tropical forest understory, which is never bright even in daytime © Bruno Henning, Wikimedia Commons:

But one creature is already busily going about in the dense tangle of vegetation: the halictid (aka sweat bee) Megalopta genalis is flying from flower to flower collecting pollen and nectar, then navigating safely back to its nest.  This is one of the 250 bee species, about 1% of the total bee fauna, known to be nocturnal (active at night) or crepuscular (active during twilight, dusk or dawn). This is a surprisingly large number, considering that bees are essentially adapted for bright sunlight.

A Megalopta genalis from Panama © USGS Bee Inventory and Monitoring Lab, Wikimedia Commons:

Bees, like other insects and crustaceans, have compound eyes, which comprise thousands of independent light receptors known as ommatidia (sing. ommatidium). Images are formed by combining the input from the ommatidia, which are oriented in different directions – up, down, sideways and forwards. As a result of this configuration, image resolution is not very good. When a bumble bee hovers near you, it probably was attracted by the colour of your hat or your scent: it just wants to check whether you are a giant flower. Insects may not see clearly, but many of them have a large angle of view – a feature that makes flies and dragonflies so hard to catch. Some insects also see polarised light, which we can’t.

Drawing of the compound eye of a drone fly from Robert Hooke’s Micrographia, 1664:

 

a: The single-chamber camera eye of humans: spatial resolution is achieved through the lens and a concave retina. b: An insect compound eye: spatial resolution is achieved through a series of small lenses and a convex retina. Striped areas indicate regions of photoreception © Buschbeck & Friedrich, 2008

 

In addition to their compound eyes, bees and most other insects have simple eyes (ocelli). These are single lens organs to detect movement and light, and they help the insect navigate during flight. Daytime bees find their way by identifying landmarks around their nests and along foraging routes; directions and distances are also determined visually, with the help of polarised light.

Compound eyes and ocelli of the orchid bee Euglossa hansoni © Insects Unlocked, Wikimedia Commons.

But how does Megalopta genalis cope with very low light? We know that nocturnal bees can react to faint movements, see polarised light and orientate from landmarks just like diurnal bees, but how they do these things is not completely clear. Night-flying bees have larger compound eyes and ocelli when compared to diurnal bees, but there must be other factors at play such as neurological adaptations; eyes alone don’t explain their visual performance.

The ability to fly at low light evolved independently in bees from the families Andrenidae, Apidae, Colletidae and Halictidae, so there must be selective advantages to being nocturnal or crepuscular. They may be less vulnerable to parasites and predators, or there could be less competition for food. The night fliers may be responding to food availability: many plants bloom only at dawn or at night to save water, while others accumulate nectar through the night, offering rich rewards to early risers.

If you are wondering whether these night-time comings and goings have any consequences for plants, the answer is yes. Nocturnal bees pollinate a range of plants, many of economic importance. Several of these bees are good at buzz pollination, so they may be particularly valuable for plants with poricidal anthers such as Solanum spp. (e.g., aubergines, peppers and tomatoes). But we know little about nocturnal bees: collecting data on pollination ecology is hard enough during day-time, and it becomes a real challenge when the lights are out.

Night-flying bees are representatives of a vast number of nocturnal flower visitors such as moths, whose role as pollinators are becoming increasingly recognised. We need more night owl ecologists to help us understand better their role in our ecosystems.

Nocturnal bees that visit flowers of Campomanesia phaea, whose fruits are eaten raw or prepared into jellies, sherbets or juices. A: Ptiloglossa latecalcarata; B: Ptiloglossa sp.; C: Megalopta sodalis; D: Megommation insigne © Liporoni et al., 2020:

Readers’ wildlife photos

February 4, 2023 • 8:15 am

Today we have a “late summer mix” of photos sent in September by reader Ruth Berger. Her notes are indented, and you can enlarge the photos by clicking on them. 

Here is what I recently caught on walks in Frankfurt near a semi-natural part of the Main river with my 28mm automatic camera.

The perennial pea (Lathyrus latifolius) is a favorite fodder of the violet carpenter bee (Xylocopa violacea) and this year, without fail, wherever there were there were peas there were (carpenter) bees.

Xylocopa violacea is striking due to its large size and iridescent black color. They like a warm-temperate climate and have recently moved north of 50 degrees latitude in continental Western Europe, where 50 degrees at low altitude can now be said to be warm-temperate, very different from 50 degrees latitude in Canada. I’ll add a photo I took in March, when I found some males of Xylocopa violacea frantically patrolling a crumbling Main river sandstone wall. Presumably, females where overwintering in the cracks and holes. Here is one the males, recognizable from the rust-colored rings near the ends of the antennae, just crawling out of a hole that he had inspected.

Here is a ruddy darter (Sympetrum sanguineum) sitting on sorrel, at a place I call “behind Aldi” (our equivalent to Walmart), where I like to go to read:

The immediate vicinity of the dragonfly photo on the non-Aldi adjacent side:

As you can guess from the reeds, there is an overgrown pond there (I think it’s ground water and runoff from the business park filling a ditch), with very variable water levels. For dragonflies, frogs and myself, it’s a miniature paradise.

This very small bee on ragwort, either Megachile sp. or Osmia sp. cf spinulosa, is one that collects pollen with its belly, not its hindlegs, as you can see from the yellow coloring of its underside. Species who belly-collect move their abdomen in a characteristic, belly-dance-like way when they are on a flower.

This unassuming smallish bee I frequently see on Tanacetum vulgare must be Colletes sp., possibly Colletes daviesanus, and like most bees, including honeybees, it uses the standard leggy method of carrying pollen, see the 3rd pair of legs with their yellow freight:

My camera and I are not good at birds, but this one of an Egyptian goose (Alopochen aegyptiaca) is near acceptable. The goose was all by itself—a rare thing in this species (photo taken in September, maybe it’s a seasonal thing?). They have completely colonized the Rhine-Main region now, where they were unknown a generation ago. For a time, it looked as though they were outcompeting other waterfowl, whom they aggressively chased in herd-like groups of 20, 30, 40 individuals. But the population seems to have crashed at some point, and at the moment, they are just one more anatine species at the river, without sticking out. I guess it is mallards who suffer most from their competition, being smaller and far less clannish, and mallards seem rarer here now than they used to be.

Here is the “indigenous” eponymic Eurasian goose, Anser anser, the greylag goose, taken a few days before the first rains (we had a record-breakingly dry summer, followed with ample rain in September):

Apatura ilia, the lesser purple emperor, is a butterfly that comes in two sex-independent morphs, one blue/purple, the other red/rust. Here is the red morph, Apatura ilia f. clytie, licking water or minerals at the river edge:

I watched it move around for a while, and got the impression it was in some pain or slightly restricted in movement from the wing damage. It could still fly, though. Willows, the caterpillar food,  grow nearby in the form of Salix alba. A picture of the blue morph, taken at the same location in an earlier year, is here if you scroll down a bit.

My final ones are of hoverflies, a group that unjustly tends to get overlooked among pollinating insects. Different from Lepidoptera (butterflies), whose caterpillars can be agricultural/forestry pests, hoverflies are wholly beneficial for humans, at least to my knowledge. Both pics were taken on windy, rainy, cool days that signaled the beginning of autumn.   This fragile beauty must be from the Eupeodes genus, but I’m not at all sure about the species (cf. nielseni), as the speckles were clearly white, not yellow:

The other hoverfly, likewise sitting on common chicory (Cichorium intybus), is Dasysyrphus tricinctus—and that’s all for today:

Readers’ wildlife photos

February 2, 2023 • 8:15 am

Again I appeal to readers to send in their good wildlife photos. Let’s keep this feature going!

Today’s post features photos by stalwart regular Mark Sturtevant. Mark’s captions and IDs are indented, and you can enlarge the photos by clicking on them.

Here are insect pictures from two summers ago.

I had recently shown the European earwig, Forficula auricularia, and here we go again. The rear pincers are modified cerci appendages that many insects have. Cerci are commonly used as sensory appendages, but earwigs have adapted them for a number of uses that include defense, handling prey (they are omnivores), and males use them for jousting. Toward that end, earwig cerci are dimorphic between the sexes. The first picture is a female, and the next are males. Besides being larger, male cerci come in different sizes and sometimes they are asymmetric. You can see males fighting with their cerci in this video. It also explains why some cerci are a bit lopsided.

There seems to be some debate about name “earwig”. There is the myth that they may crawl into peoples’ ears, but another claim is that the name has to do with their remarkable hind wings that are ear-shaped when unfolded. The unfurling of their wings is pretty impressive, and you can see that in slow motion below:

Next is a picture of a spined assassin bug, Sinea diadema. This is a predatory insect.

I was in the woods one day when I came across this unidentified leaf beetle (Chrysomelidae) in a bush. I was negotiating how to photograph the beetle, but a stink bug nymph suddenly appeared from behind and impaled it! Some stink bugs are predators, and I have seen them with dispatched prey that are much larger and more powerful than they are. One can fairly wonder how such slow insects might be predatory, but I guess it just takes a poke from their proboscis and their victim is secured. The stink bug is Podisus sp.

The beetle dragged the bug behind for several minutes, but the bug grimly hung on. Meanwhile, a bundle of needle-like styli would be scissoring their way into the beetles’ innards, and digestive juices would be injected.

Gradually, the beetle began to slow, and then it was immobilized. A small murder in the woods!

Next up is a two-striped planthopper, Acanalonia bivittata. “Planthoppers” encompass a number of insect families, this one being Fulgoridae. There are also “leafhoppers” and “treehoppers”. One day I should try to memorize what the differences are supposed to be. All of these and other related families were once in their own insect order, the Homoptera (“uniform wing). But now they are awkwardly but I expect correctly absorbed into the order Hemiptera (“half wing”), along with the above stink bug.

Here is a nymph of what is likely the two-spotted tree cricket, Neoxabea bipunctata. This is a young male, and you can see it is developing the specialized front wings that are used by males for chirping, and the larger fan-like hind wings which they fly with. In adults, the hind wings are of course folded up and covered by the front wings. But at this earlier stage the position of the wings are curiously reversed so that the hind wings cover the front wings.

I had found this tiger beetle that was disabled, and so I could pick it up. Tiger beetles are predators that use their good vision and considerable speed to tackle small prey. There is dispute about the taxonomy of this group. They had long been placed in their own beetle family (Cicindelidae), but others have placed them within the ground beetle family (Carabidae). I can say only that there are many ground beetles that resemble tiger beetles, and tiger beetles that look like ground beetles, and whatever side you are on there is agreement they are closely related. Tiger beetle mandibles look pretty imposing, but the bite strength of this small one isn’t detectable. I did not think to get the species.

Next is a large ichneumon wasp, Megarhyssa macrurus, which had apparently recently emerged as an adult and was not quite ready to fly. The extraordinary ovipositor hanging off the rear is considerably longer than its body, and is used to drill into wood to lay an egg in a wood-boring sawfly larva.

Finally, I expect that most people know that scorpions fluoresce under UV light. Actually, UV fluorescence appears here and there among arthropods in general, and plants will also fluoresce under UV. It’s fun to go out at night with an inexpensive LED UV flashlight to see what turns up.  Your own back yard becomes fairly transformed into a semi-alien world. Leaves, flowers, and sometimes arthropods will blaze in day-glo colors.

I had found that aphids also fluorescence under UV light. Here are poplar tree aphids (Chaitophorus populicola), first in regular light, and then under UV light. There are two issues here, though. There is some motion blur from the aphids because the exposure needed to be long. And although the aphid fluorescent color seems pretty accurate, the leaf color is wrong since it is supposed to be deep red under UV. My current flashlight is cheap, and it certainly does not put out only UV light.

Readers’ wildlife photos

January 26, 2023 • 8:15 am

Today’s contribution includes collages of moth photos by reader Aaron Hunt; the theme is “polymorphism”, or variability in appearance among individuals within a species.  The photos were taken on Block Island, off Rhode Island. You’ll have to enlarge the photos by clicking on them (preferably twice in succession with a pause between clicks).  Aaron’s narrative is indented.  Especially note the last species group, which has wing patterns mimicking salticids (jumping spiders).

The theme of this batch of images is identification. Moth identification presents a variety of challenges, not least of which are the very incomplete state of knowledge of many taxa and the enormous species diversity of the order. The more than 13,000 described species of moths found in North America north of Mexico represent less than a tenth of the global described fauna. Perhaps a thousand more Nearctic species, and probably several tens of thousands globally, remain undescribed, In principle, most moths can be identified to species from wing pattern alone, but reliable sight recognition of unfamiliar species at higher taxonomic levels takes an enormous amount of experience. At the species group level, intraspecific variability in markings often visually overwhelms the modest consistent differences between species. Identification of higher taxa is easiest using a combination of structural characters of the head, labial palpi, and antennae in combination with the subtle, basic wing pattern elements that are most resistant to change over evolutionary time scales.

Most of the images shown here are collages showing numerous individual moths to illustrate variation and differences in pattern and color. Dimensions of individual photographs in each of the four large collages range from 500×500 to 900×900 pixels, so each collage is much too large to show up here at full resolution. Each has also been compressed into a smaller jpeg to reduce file sizes. At the end of the text corresponding to each collage [JAC: Pictures are beleow the text] is a link to the image (hosted in my Google drive) at full resolution in its original png format. There, you’ll be able to view the individual moths included in the collages in much greater detail than can be shown on this page.

Macrochilo orciferalis (Noctuoidea: Erebidae: Herminiinae) — This specialist of dune habitats is bivoltine on Block Island, with adults on wing mainly in June and August. Both sexes are highly variable in forewing maculation, with several characters seeming to vary independently and with no sexual dimorphism in markings apparent. (Males, which have bipectinate antennae, are much commoner at lights than females, which have simple antennae.) One photographer on the coast of New Brunswick across from Prince Edward Island reports seeing mostly dark (like those at bottom right and one below top left in my collage) or striped (like four individuals in my collage) moths of this species, whereas I see mostly lighter specimens on Block Island. One wonders what mix of environmental and genetic factors underlie color and pattern variation in this species and what selective forces sustain it. Click here for the collage at full resolution.

Hypsopygia olinalis (Pyralidae: Pyralinae) — This species is quite common on Block Island, where it is univoltine, flying June through early August. (I have seen a handful of fresh specimens in August and September that are either extreme stragglers or overly precocious offspring of the main generation; either way, I imagine any offspring they produce fail to complete development so far out of season. Still, this phenomenon illustrates how species can adapt to changing climate; if Block Island’s climate warms enough in the coming decades, some populations not quite able to complete a second generation each season will become able to do so with a slightly longer growing season.) Adults vary dramatically in coloration from pale greenish yellow to a dark brick red. This variability helps to make the species easy to confuse with a few similar congeners with overlapping ranges in eastern North America. I photographed all the moths in this collage on a single sheet one night last June. Unfortunately, I just now noticed that I missed a duplicate, so I got good photos of only 19 individuals, not 20 — see if you can spot the moth shown twice. Click here for the collage at full resolution.

Phyllocnistis Vitaceae feeders (Gracillariidae: Phyllocnistinae) — At least two or three species form long, narrow leaf mines in plants in the grape family (Vitis and Parthenocissus) in eastern North America. Species boundaries need to be sorted out in this species complex of minute moths. On Block Island, mines in the Virginia creeper around my yard yield at least two generations of moths that regularly come to lights. Adults in the summer generation (large photo) are shining white with faint black and yellow markings in the distal half of the forewing; those in the fall generation (small photos at right) are somewhat to much more strongly and extensively marked. This species complex offers a good example of seasonal dimorphism as well as confounding external similarity of same closely related species.

Acleris (Tortricidae: Tortricinae: Tortricini) — A number of species in this large, mostly Holarctic genus are highly polymorphic. The group has been popular with collectors since the dawn of modern taxonomy, with European lepidopterists naming up to dozens of color forms for some species from the early 19th century to the early 20th century. Very similar color forms often occur in two or more polymorphic species; genitalic dissections finally established species boundaries in the early- to mid-20th century. Block Island is mercifully short on polymorphic Acleris, with only two similar species present. The island’s population of flavivittana exhibits four highly discrete color morphs, two of which closely resemble the two local color morphs of robinsoniana. A non-polymorphic species found on Block Island, inana, very closely resembles one of the local morphs of flavivittana and somewhat less closely the corresponding robinsoniana morph, which happens to be the predominant of the two. At least inana is univoltine, though its flight window overlaps with those of second generation flavivittana and robinsoniana. Another species found on Block Island, maculidorsana, resembles inana. All four of the aforementioned species are pictured in the collage below, and in a sensible arrangement, but I’ve left identifying the specimens as a challenge to the reader. For the answers and the full resolution version of the collage, click here.

Euxoa detersa (Noctuoidea: Noctuidae) — With 182 species currently recognized in North America north of Mexico, Euxoa is one of the most speciose genera on the continent. Euxoa is primarily a genus of arid and semiarid habitats of the northern hemisphere and is nearly absent from tropical and humid subtropical habitats. Nearly all New World Euxoa are found in the western US and Canada, where some species are among the most abundant medium-large moths. About 30 occur in eastern Canada, but most of them are species of boreal forests found across the continent. Only five species are found in eastern deciduous forests, and only three aridland species occur on the Atlantic Seaboard; the genus is entirely absent from most of the Southeast US. Despite being very well studied, Euxoa presents a daunting identification challenge in western North America. Many species are highly variable in pattern and color, and some closely related species covary in maculation across habitat gradients. Characters of wing maculation recur across and vary greatly within phylogenetic species groups, making subgeneric taxonomy of little use in narrowing down identification possibilities using only wing markings. Just a few Euxoa species occur on Block Island, and telling them apart is straightforward. However, the island’s population of Euxoa detersa, which flies in abundance in dune habitats throughout September, provides a striking example of the remarkable variability so many Euxoa species exhibit. The image shown here depicts 49 individuals of this species from Block Island and is cropped for size from a larger collage of 121 individuals. Click here for the uncropped version at full resolution.

Tebenna sp. (Choreutidae), Eoparargyractis plevie (Crambidae: Acentropinae), Chalcoela iphitalis (Crambidae: Glaphyriinae), and Eucosma annetteana (Tortricidae: Olethreutinae: Eucosmini) — These species are all mimics of jumping spiders (Salticidae). Jumping spiders are highly visual ambush hunters and among the top predation threats to small moths. Salticid mimicry has evolved a few dozen times in more than a dozen moth families globally, producing very strong convergence in wing maculation in many completely unrelated groups of moths. It has evolved in other insect orders as well, including numerous times in planthoppers (Hemiptera: Fulgoroidea). Salticid-mimicking moth lineages are easily mistaken for each other and often are very different from their closest relatives in superficial appearance. Salticid mimicry in Lepidoptera is little-studied, but the few species studied have been found to produce aggressive displays in jumping spiders, resulting in markedly lowered rates of predation success.

Readers’ wildlife photos

January 20, 2023 • 8:15 am

Thanks to those who sent in photos. We have anough to last about a week.

Today we have a photo-and-text story from Athayde Tonhasca Júnior. His narrative is indented, and you can click the photos to enlarge them.

The itsy bitsy influencers

Arachne, born in the ancient kingdom of Lydia, was really good at weaving. A masterful weaver, perhaps, but not wise. She boasted to the world about her skills, claiming she was better than Athena herself, the goddess of handicrafts. All that braggadocio reached heavenly ears, and the offended goddess thought it was time to take down the impertinent Lydian a peg or two. Disguised as an old woman, Athena appeared before Arachne and warned her that stirring up the gods could end in tears. Arachne not only ignored the old biddy’s advice but challenged her to a weaving contest. Athena revealed her true identity and shrieked back: “you’re on, she-dog!” (or words to that effect; translations vary). Proving beyond doubt she wasn’t wise, Arachne didn’t back down. Worse: she created a superb piece, but of tabloid content. Her tapestry depicted the unconventional liaison between a swan (Zeus in disguise) and Princess Leda, and Zeus cross-dressed as a satyr and as an eagle during other dalliances. Arachne also wove various romantic transgressions by members of the royal family such as Apollo, Dionysus and Poseidon.

Despite admitting defeat to the better weaver, Athena was incensed and humiliated – after all, Zeus was her daddy. She tore Arachne’s work to pieces and destroyed her loom. For Arachne, the drachma finally dropped. Horrified by her recklessness, she hanged herself. Athena, who acquired the post of goddess of wisdom, decided that the silly mortal had learned her lesson. She turned the hanging rope into a cobweb and brought Arachne back to life, but not as before. In Metamorphoses, Book VI, Ovid tells us what happened (translated by A. S. Kline): “Arachne’s hair fell out. With it went her nose and ears, her head shrank to the smallest size, and her whole body became tiny. Her slender fingers stuck to her sides as legs, the rest is belly, from which she still spins a thread, and, as a spider [arachni in Greek], weaves her ancient web.” Hereafter, Arachne’s descendants would hang from threads and carry on as skilled weavers.

Minerva (the Roman version of Athena) cancelling Arachne for her hate speech against the gods. Art by René-Antoine Houasse, 1706. Wikimedia Commons:

Arachne’s chronicle is one of the many myths, legends and symbolisms involving spiders (Class Arachnida, Order Araneae) in Western cultures. Despite their relevance in the humanities, spiders tend to provoke a range of negative emotions in people: fear, revulsion, loathing. Indeed, children of school age fear spiders the most, ahead of being kidnapped, predators or the dark. the American Psychiatric Association recognises arachnophobia, the persistent and irrational fright caused by spiders, as a mental disorder that afflicts a number of people. The innate fear of spiders and snakes is likely to be a remnant behaviour acquired during our evolutionary history for identifying and avoiding animals that could be harmful to us (e.g., New & German, 2015. Evolution and Human Behavior 36: 165-173).

Helping children to sleep peacefully: Little Miss Muffet is about to make an acquaintance. Art by Arthur Rackham, 1913. Wikimedia Commons:

Spiders’ negative image is not helped by misinformation: Mammola et al. amassed data from newspapers in 40 languages around the world and concluded that about half of the news was erroneous, misleading or sensationalist. This is deeply regrettable, as spider incidents involving humans or domestic animals are exceedingly rare, especially considering how abundant they are: you could bump into 130 to 150 individuals/m² in some habitats. But you are not likely to see most of them because they are small, nocturnal or hunt among the soil debris. The 45,000 or so known spider species are spread throughout practically every terrestrial habitat in the planet. Instead of biting people, spiders spend most of their time stalking or chasing unsuspecting prey (except for one herbivorous species, the wonderfully named Bagheera kiplingi). They are generalists, pouncing on whatever comes within their reach.

Insect pollinators have reasons to be particularly wary of one group of spiders: the crab or flower spiders (Family Thomisidae). Most of them are ambush predators: they sit perfectly still on a spot likely to be visited by insects, such as a flower, and wait for lunch to fly in. To make things worse for an inattentive insect expecting to collect pollen or get a sip of nectar, many flower spiders show some degree of crypsis, the ability to blend in with their environment to avoid detection (different from mimicry, which is disguising by resemblance to another organism). We can just say that flower spiders are very good at camouflage.

A female white-banded crab spider (Misumenoides formosipes) on a stakeout. She can change her colour between yellow and white to match the surroundings © Judy Gallagher, Wikimedia Commons.

Interestingly, flies are less susceptible to spider predation than bees, possibly because they have better vision and can avoid or dodge attackers. Bumblebees are also less likely to become prey than are solitary bees and honey bees, just because they are larger and bulkier and so more difficult to capture. It has been suggested that the long proboscis and the swing-hovering flying pattern of some moths have evolved as predator avoidance mechanisms: the further from the flower and less static, the better chance of escaping a lurking spider. But it’s not only through killing that spiders disrupt pollination: their mere presence results in insects making fewer visitations and spending less time on flowers. As a result, pollination rates and therefore seed production can be reduced (e.g., Romero et al., 2011. PLoS ONE 6,6: e20689).

Game over: a female crab spider (Thomisus onustus) capturing a bee © Alvesgaspar, Wikimedia Commons.

From the above, you may be tempted to go on a spider-killing spree in your garden to protect pollinators and pollination. That would a mistake. We have a limited understanding of the effects of predation on pollination, but there are no reasons for alarm. The numbers of flower visitors killed represent a fraction of their populations, so a spider wipe-out would not help anything. And because of the complexity of these interactions, there could be damaging consequences.

The crab spider Thomisus onustus, found across Europe, reduces bee visitation to buckler-mustard (Biscutella laevigata) flowers. But spiders have no preference for bees: they will take anything that comes their way. So insects that feed on vegetative parts (leaves, petals, etc.) are likely to be the spider’s main victims just because they are more abundant than pollen or nectar collectors (Knauer et al., 2018. Nature Communications 9, 1367). Without the spider, buckler-mustard could be munched away with impunity.

Crab spiders feeding on a furrow bee (Halictus sp.) and a cabbage moth caterpillar (Plutella xylostella) © A.C. Knauer (Knauer et al., 2018. Nature Communications 9, 1367):

In South America, the stingless bee Trigona spinipes visit fewer flowers of the pea-related Chamaecrista ramosa when crab spiders of the genus Misumenops are about. Which is good from the plant’s perspective because these bees are pollen robbers, that is, they help themselves to pollen without pollinating the flowers. But the carpenter bees Xylocopa ordinaria and X. hirsutissima, which are legitimate pollinators of C. ramosa, are not put off by the spiders, probably because they are too big and strong to be captured (Telles et al., 2019. Biological Journal of the Linnean Society 126: 521–532). So hosting a bee predator with restricted hunting abilities may be beneficial to the plant.

A Mesumenops bellulus ready to give a deadly embrace, but not to portly carpenter bees © Judy Gallagher and Bob Peterson, respectively. Wikimedia Commons:

Spiders are one of most important groups of predators on Earth, with enormous influence in the natural world. Nyffeler & Birkhofer estimated that spiders kill the equivalent of 400 to 800 million metric tons of prey annually worldwide. More than 90% of this biomass comprises springtails and insects, including a vast number of domestic and agricultural pests. For comparison, the annual food consumption of all the world’s seabirds is estimated at 70 million tons.

Tables set for lunch. For an insect, it’s dangerous out there:

Spiders’ carnage is hugely beneficial: it regulates the numbers of abundant species, preventing them from taking over, and keeps insects with outbreak potential (pests) in check. And they are also essential food items to other creatures: wasps, frogs, lizards, birds and even fish feed on spiders, sometimes substantially.

You don’t have to be fond of spiders; but being aware of their ecological importance would make them more accepted and valued, even if at distance.

To the delight of women’s rights champion J. K. Rowling, a new species of spider discovered in India in 2016 was named after Godric Gryffindor of sorting hat fame (Harry Potter series): Eriovixia gryffindori. New spider species are discovered all the time © India Biodiversity Portal and Suzelfe (Wikimedia Commons), respectively:

Johnny Cash, ‘The Man in Black’, was the source for the name of a new species of tarantula whose males are usually black: Aphonopelma johnnycashi. The spider was discovered near the California prison that inspired Cash’s song Folsom Prison Blues (1955). A. johnnycashi is one of the 14 new tarantula species recently found in the United States (Hamilton et al., 2016. Zookeys 560: 1-340) © Hamilton et al., Wikimedia Commons.

Readers’ wildlife photos

January 11, 2023 • 8:15 am

Today’s reader introduces himself and his pictures below. Semyon’s words are indented, and you can click the photos to enlarge them. I believe this is the first Russian contributor we’ve had. Welcome!

My name is Semyon Morozov. I’m sending you my wildlife photos.

These photos were taken in August 2016 in my small homeland, Kurgan Oblast (Russia, the south of the West Siberian Plain). Photo hunting was successful at that time!

Here’s a female wasp spider (Argiope bruennichi). Look at these white things on her web: they are called stabilimenta. Their function is not completely clear. Scientists assumed that these structures stabilized the web, but then other explanations appeared, such as protection from predators or attracting prey.

Eurydema ventralis is a shield bug that feeds on crucifers and some other plants. The bug sits on a leaf of Parthenocissus that has been cut by a leafcutter bee (Megachile sp.).

The yellow-winged darter (Sympetrum flaveolum) is one of the most common dragonflies in this area.

This is an odd caterpillar of the grey dagger (Acronicta psi). It was ready to pupate, so I took it home for observation.

But instead, a fat larva of some parasitoid wasp crawled out of the caterpillar! Then the larva pupated, and after 16 days an imago appeared from the pupa.

And here’s the Roesel’s bush-cricket (Roeseliana roeselii). This individual has a saber-like ovipositor at the end of the abdomen, which indicates that it’s a female.

All these arthropods were dwellers of the garden. Now let’s go beyond it. What are these cupcake-like things on the rotten stump? These are the fruiting bodies (aethalia) of the slime mold (Fuligo septica, I guess). These are not fungi but organisms, the life cycle of which includes both a single-celled amoeba-like stage and a macroscopic one.

In the meadow, I found a wasp spider again. This female caught another predator, a dragonfly (it’s most likely the yellow-winged darter).

There was a pond nearby, next to which I met a caterpillar of the drinker moth (Euthrix potatoria). It’s said that the insect was so named because of the caterpillars’ passion for dew.

I found another caterpillar on the pond shore. It was a larva of the reed dagger (Symira albovenosa = Acronicta albovenosa), a moth that likes reed beds.

And finally, here are exuviae of some dragonfly. These are the remains of an exoskeleton that a larva left after molting.

Readers’ wildlife photos

January 5, 2023 • 8:15 am

Today’s photos of dragonflies come from Mark Sturtevant. His captions and IDs are indented, and you can enlarge his photos by clicking on them:

On a different website where one shares pictures of arthropods, I have for many years run a series that for some reason I call “Dragontowne”.  Dragontowne is an imaginary place where one can wander around and meet my favorite insects, which are dragonflies. So next stop, Dragontowne!

First up is a female calico pennant (Celithemis elisa) in the skimmer family (Libellulidae). Pennants generally have boldly marked wings, hence the name. The picture is focus stacked from a few pictures taken by hand. These lovely but small dragons always perch at the tops of plants, so one generally must sneak up and stand directly over them to get this view.

Clubtail dragonflies belong to the family Gomphidae, and are named after the enlarged end of their abdomen. As with the hobby of birding, those who chase dragonflies can refer to informative websites to learn where particular species of dragons may be found. According to online informants, there is a park about 2 hours drive away from me (in eastern Michigan) that hosts at least 12 different species of clubtails! The conditions there are perfect, with a clean gravel-bottomed river that loops around this park so the fields in the park become the main patrol ground for all kinds of dragonflies over several miles of river. So I go to this park when I can.

I have only a handful of local clubtail species yet to photograph, thanks to this place, and last summer I managed to get one of the “big club” species called the skillet clubtail (Gomphurus ventricosus). The name is inspired by the wide, frying-pan like club. This male had gotten hopelessly entangled in the weeds and could not fly out, so I rescued it. Photographing dragonflies in hand and getting close-ups of the abdomen is a standard thing to do for dragonfly enthusiasts since one can then document certain structures that are diagnostic to the species. But I don’t routinely catch dragonflies for fear of harming them. There is one more big club species to go, known as the cobra clubtail. They are in the field, but so far no luck at getting close enough.

“Snaketails” are a group of clubtails that tend to have a lot of green and brown coloration instead of the yellow and black markings of other clubtails. There are two species in this field, and here is the more common one: the rusty snaketail (Ophiogomphus rupinsulensis).  The 2nd species is a tiny dragonfly called the pygmy snaketail, but it is very rare in my area and I have yet to even see one. 

Spiketail dragonflies (family Cordulegastridae) seem similar to clubtails in that they have yellow and black markings. Their common name refers to the stinger-like ovipositor that females use for laying eggs in the sand, and you can see that in the linked picture. Spiketails behave quite differently from other clubtails in that they fly for very long periods, while most clubtails are outright lazy in comparison. Spiketails are associated with forests, staying close to the clean woodland streams in which they breed.

The scuttlebutt online reports that one species, the spectacular arrowhead spiketail (Cordulegaster obliqua), may be found in my area along a particular woodland stream. So off I went, pretty much just to photograph this dragonfly. They were common, but all were males intent on continually patrolling the stream for females. After a couple long visits with no luck at seeing a single landing, I just had to just break down and catch one. So back to the car I went to retrieve a butterfly net. Back at the river I managed to catch one (first try!), and here it is. In the 2ndpicture you can see why they are called arrowheadspiketails. Of course he was released afterwards.

Darner dragonflies (family Aeshnidae) are next. First is what I believe might be a lance-tipped darner (Aeshna constricta). This is one of the “mosaic” darner species that tend to look quite similar to each other, so I am often not sure of their ID. Whatever it is, this is a female. 

 The second darner is unmistakable. This is a male fawn darner (Boyeria vinosa) that surprised me at the end of a long day in the woods by flying up from behind and landing right in front of me. Fawn darners spend much of the day roosting in foliage, becoming active later in the afternoon where they continue to fly through sunset and even until it gets quite dark. So they are semi-nocturnal dragonflies. Fawn darners have a distinctly wimpy and fluttery flight when they are just on patrol, but when they see something to chase they suddenly become as nimble as any dragonfly. By happenstance, the linked picture includes an interesting story about extremely tiny wasps that parasitize dragonfly eggs. I had no idea about those! 

The next picture is something new for me. I’ve been wanting to photograph aquatic insects, so I built a kind of glass bottomed tray out of a picture frame. This was used here for the first time to photograph a young dragonfly “naiad”, which is the term for their aquatic stage. An online friend told me that this is one of the baskettail dragonflies (family Corduliidae). The common name refers to how adult females will carry an egg mass, clasped with appendages at the tip of their abdomen.

And finally, the last stop in Dragontowne shows a male widow skimmer (Libellula luctuosa) — a member of the skimmer family once again. I just like the composition and memories of hot summer days that it brings.

Readers’ wildlife photos

January 2, 2023 • 8:15 am

Today we have the first contribution of the year by Athayde Tonhasca Júnior: one of his patented word-and-photo stories. His text is indented, and you can enlarge his photos by clicking on them.

How beauteous mankind is! O brave new world,
That has such people in’t.

—William Shakespeare, The Tempest

1

Mr McGuire: I want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr McGuire: Are you listening?
Benjamin: Yes, I am.
Mr McGuire: Plastics.

Mr McGuire was prescient in his advice to young Benjamin Braddock about his career options (The Graduate, 1967): the plastics industry has since expanded to levels unimaginable then. Cheap, versatile, resistant and durable, plastic products are essential in today’s society. They are everywhere. So, unsurprisingly, they are an ever growing environmental problem: land, waterways and the oceans are stuffed with discarded plastic.

Plastic rubbish is a blight on the landscape, but some birds and mammals have taken advantage of this abundance of material. Squirrels and opossums have learned to use straws, string and plastic bags for nest building; plastic fragments were present in about 14% of surveyed nests of the brown booby (Sula leucogaster), a seabird found around the world. So, diligent nest builders such as leaf-cutter bees (genus Megachile) were bound to join this team of opportunists.

Most leaf-cutter bees cut pieces of leaves or petals to build their nests; some use mud, pebbles or resin as construction materials. These bees usually nest in sheltered natural cavities such as burrows, crevices and hollow twigs. They are important pollinators, and a few species have been reared commercially for crop production, such as the alfalfa leaf-cutter bee (Megachile rotundata).

A Megachile centuncularis at work. This is one of seven megachilid bees in Britain © Line Sabroe Wikimedia Commons:

A leaf-cutter bee nest © Subbu Subramanya, Wikimedia Commons:

In Ontario, Canada, alfalfa leaf-cutter bees have been creative and resourceful by using pieces of polyethylene-based shopping bags as a building material. Another local species, the bellflower resin bee (Megachile campanulae), constructs nests with plant resins instead of leaf and stem segments. It has no use for plastic bags, but polyurethane-based sealants, which are applied to the exteriors of buildings, offer a handy and abundant alternative. Some bellflower resin bees mixed this plastic product with natural resins to build their nests.

Brood cells partially constructed with polyethylene plastic bag fragments (L,) and polyethylene resin © MacIvor & Moore, 2013. Ecosphere 4: 1-6

Rural areas are not exempt from the plastic deluge. In the Argentinian countryside, bits of greenhouse covers, agrochemical containers, fertilizer bags and irrigation hoses combine with the ubiquitous shopping bags to deface the landscape. One bee, possibly an alfalfa leaf-cutter bee, took advantage of this clutter to do away with leaves or petals completely: she built an entire nest with pieces of two types of plastic.

A plastic nest of Megachile sp. built in a nest trap © Allasino et al., 2019. Apidologie 50: 230–233:

We don’t know whether plastics have any effect on leaf-cutter bees. They may be neutral, or even beneficial; plastics may act as a barrier against fungi and parasites, which are important mortality factors for solitary bees. On the other hand, these impermeable materials may trap water and thus increase the brood’s susceptibility to diseases.

By using plastics, bees have demonstrated their ability to identify alternative and convenient resources, and to adjust to changes in their environment. All the same, plastic nests are another troubling sign of a world living in the Anthropocene. From the Greek anthropos (man) and cene (new or recent), this unofficially labelled geological epoch applies to Earth’s history since humans started to have a significant impact on climate and ecosystems. It’s a new world of mass extinctions, deforestation, pollution, fossil fuels, and climate change. Perhaps leaf-cutter bees can adapt and even flourish in this world. We may do the same. Or not.

2

In 1926, the British government’s Central Electricity Board set out to create a nationwide electrical grid to bring cheap power for everyone. This was the biggest building project that Britain had ever seen, and soon steel pylons and transmission lines began popping up all over the landscape. And many people didn’t like what they saw. In 1929, Rudyard Kipling and John Maynard Keynes co-signed a letter to The Times objecting the construction of pylons, noting they were ‘the permanent disfigurement of a familiar feature of the English landscape.’ The pylon’s designer, architect Sir Reginald Blomfield, fired back: ‘Anyone who has seen these strange masts and lines striding across the country, ignoring all obstacles in their strenuous march, can realise without a great effort of imagination that [they] have an element of romance of their own. The wise man does not tilt at windmills – one may not like it, but the world moves on.’

You may side with Kipling and Keynes or Blomfield in this aesthetics vs utility debate, but transmission lines are here to stay, for a while at least. The British grid of high-voltage lines from power stations alone runs for ~25,000 km; adding to that several thousand kilometres of regional networks, power lines have become part of our landscape.

Transmission corridors, similar to roadsides and railway embankments, are routinely mowed, clear-cut or treated with herbicides to prevent the encroachment of trees and dense vegetation. These practices are viewed as necessary evils by the public and some conservationists; but, with the right touch, they create opportunities for bees and other pollinators.

In ecology, ‘succession’ is the process by which a natural area changes after a disturbance or following the initial colonization of a new place. In terrestrial habitats, early succession refers to the period before they become enclosed by trees’ canopy. Weedy areas, grasslands, old fields or pastures, shrub thickets and young forests are all examples of early successional habitats. And so are transmission corridors, where maintenance crews prevent succession from reaching its equilibrium point or climax by cutting down the vegetation.

Plant succession © CNX OpenStax, Wikimedia Commons:

It turns out that habitats in the early successional stages are excellent for bees. These areas offer a steady supply of nectar and pollen over much of the year, as opposed to forested areas where blooms peak in spring and are limited by the shaded canopy from midsummer on. The large majority of bee species nest in the ground; they need patches of bare soil of the right texture and moisture levels, and close to their food plants. Successional habitats are just the right place for this combination of features. So it’s not surprising that bee abundance and species richness decreases with increasing forest cover.

Lots of flowers, nesting/hibernation sites & sunshine: perfect for bees © Mick Garratt, Wikimedia Commons:

In the north-eastern United States, energy companies have been maintaining power lines under Integrated Vegetation Management (IVM) since the 1950s with the objective of protecting the grid while providing habitat for threatened plants and animals. It sounds fancy, but essentially IVM comprises five-year cycles of selectively killing trees (mechanically or with herbicides), with no mowing or widespread spraying of herbicides. These simple techniques create a mosaic of meadow, herbaceous plants and shrubs, which have proved to be good for many reptiles, amphibians, birds, small mammals, and bees. A comprehensive survey along 140 km of a transmission line in New England revealed that the sunny, open corridors held nearly 10 times the number of bees and twice the number of bee species as compared to adjacent forested areas. Not only that, about half the known species for the region, including some rarities, were found in the survey (Wagner et al., 2019.  Biological Conservation 235: 147-156).

A power line corridor, great habitat for bees © Mark Nenadov, Wikimedia Commonns:

Not everybody likes the sight of a transmission line. But these ugly and gloomy steel towers and cables can be turned into pollinator and wildlife havens. All it takes is goodwill and some imaginative work. The lights will stay on, and there will more bees around.

3

The Milky Way galaxy has awed civilizations and inspired many philosophical thoughts about mankind’s insignificance, our place in the big scheme of things, the fleeting nature of life, and what it’s all about. But if young Europeans or Americans are asked to share their impressions about the Milky Way, responses are likely to be limited to a shrug or a puzzled look: about 60% of Europeans and 80% of North Americans have never seen it. When Los Angeles went through a blackout in 1994 because of an earthquake, emergency services received several calls from nervous citizens about a giant, strange, silvery cloud in the dark sky. These Angelinos were seeing the Milky Way for the first time.

The Milky Way, unseen by many © Oliver Griebl, Wikimedia Commons:

As the human population increases and concentrates more and more in cities, the world becomes more illuminated. Artificial light at night (ALAN) is an ever-growing phenomenon because of the lighting of streets, parking lots, roads, buildings, parks, monuments, airports, stadiums – basically any manmade structure. This artificial light is scattered into the atmosphere and reflected back, particularly by clouds, creating a nighttime sky luminance known as ‘sky glow’. Excessive illumination and artificial sky glow spread way beyond urbanized areas, essentially contaminating the whole landscape with light: nighttime darkness is disappearing.

Glow in the sky from Helsinki seen in Estonia © Bilovitskiy, Wikimedia Commons:

Light pollution is an ecological disturbance with multiple consequences. ALAN disrupts natural day-to-night rhythms such as singing and migration of birds, the activity period of small mammals, mating of frogs, nesting of bats and the orientation of sea turtle hatchlings. There is increasing evidence that humans are also sensitive to ALAN: it affects our circadian rhythm (the sleep–wake cycle repeated approximately every 24 hours), resulting in irregular hormone production, depression, insomnia and other maladies.

Insects couldn’t be immune to the effects of ALAN since much of their behaviour is dependent on light. We don’t know how insects see the world, but they recognize forms, detect movements and discern colours based on lighting patterns. Insects can monitor the position of the sun by the polarization of light, so they can navigate with precision. Light detection helps them to keep track of the photoperiod (day length), which is fundamental to preparing for the winter months.

Many beetles, flies, lacewings, aphids, dragonflies, caddisflies, wasps and crickets are drawn to light, but moths’ compulsive and apparently suicidal attraction to lightbulbs or flames is the most familiar case of positive phototaxis (moving towards a light source) among insects. Moths are important pollinators, so naturally their possible vulnerability to killer lights is a matter of concern.

A fatal attraction © Fir0002, Wikimedia Commons:

It turns out that moths’ fatal attraction doesn’t seem to be that fatal because they are only drawn to light at relatively short distances. A few moths come to a blazing end, but most of them are beyond light’s dangerous pull. This is not to say that moths are safe from ALAN. When the night is not sufficiently dark, egg-laying and production of sex pheromones are inhibited for some species, so that their reproduction is affected. Also, the window of time for courtship and mating can be severely reduced. Light pollution interferes with moths’ perception of colours and shapes, signals necessary for flower location. It also makes them more vulnerable to parasites and predators, either because they are easier to find, or their defence mechanisms (e.g., bat avoidance manoeuvres) are less effective in over-illuminated environments.

Light pollution disturbs many aspects of moths’ physiology and behaviour, although we can’t tell whether whole populations are being harmed: not all species respond equally, and there are many variables to be considered about the light source, such as wavelength, intensity, polarization and flicker. But from the little we know, excessive illumination can be added to the list of pressures on our moth fauna and consequently on pollination services.

At a time of growing concern about global warming, light pollution may sound like a secondary problem. But the more researchers look into it, the more they learn that this is a serious environmental threat. And while sorting out the climatic mess will be tricky and complex, the light pollution problem is relatively easy. The first, obvious and straightforward measure is to turn off unnecessary lights. When illumination is needed, it could be dimmed, shielded or limited to specific areas such as pavements or roads. Light dimming is good for the environment and for the economy too. When in 2018 the city of Tucson, USA, converted nearly 20,000 of their street lights to dimmable LEDs, £1.4m were saved from its annual energy bill.

Preserving and protecting the nighttime environment is an important but neglected aspect of conservation. A darker world would benefit moths and other species, and it would be good for us as well. We could sleep better or go stargazing again.

World map of light pollution: colours show intensities of sky glow from artificial light sources © David Lorenz, Wikimedia Commons:

Readers’ wildlife photos

December 22, 2022 • 8:15 am

It looks as if I’ll be in Chicago over Coynezaa, so do send in your photos, and we’ll see if we can keep this feature going over the holidays.

Today’s batch of photos come from Mark Sturtevant, whose IDs and captions are indented. Click the photos to enlarge them.

First up is a bundle of assassin bug eggs. A very common species of this predatory insect is Zelus luridus, and so that is most likely what will hatch from these eggs:

The European earwig (Forficula auricularia) is commonly seen up on plants, and they can accumulate in considerable numbers. Because they nibble on flowers and leaves, gardenersgenerally view them as pests. However, they also eat small arthropods, including aphids. I like them because they are so weird looking, and their matte finish photographs so nicely. The pinchers on the rear are modified cerci (those being appendages that many insects have). When alarmed, they will curl their abdomen like a scorpion, and they do look pretty fierce that way but it’s all a bluff since they cannot pinch in the slightest. But there are claims that other earwig species can use them as weapons of a sort:

In my younger years, the pink spotted ladybeetle (Coleomegilla maculata) was a common sight, but they are pretty rare where I live now. It was therefore exciting to at last find a pink ladybeetle when I was out “bugging” with the camera, but for some reason this one wasn’t moving. One can see why in the picture. Do you see the small cocoon underneath the beetle? That is the cocoon of a parasitic Braconid wasp! So this beetle was unfortunately parasitized, and its body was being used as a kind of protective shield:

Wolf spiders are most active at night, and then they can be easily found by using a flashlight to spot them through their brilliant eye-shine. So I went out to a remote park one evening to look for wolf spiders. The experience was rather startling, since a walk through the woods at night (which was a bit creepy, to be honest) revealed a veritable milky way of tiny glowing green eyes lighting up the trail. The wolf spiders on the trail were all small, but I had no idea they would be so numerous! After about a mile, the woods opened up to a large field and a full moon. More tiny glowing eyes, but not so many. Then I came across a set of eyes that were much bigger, and behind those was a very big wolf spider! A strikingly colored female. After admiring her, she was respectfully scooted into a bug cage. A bit more searching turned up a male of what was clearly the same species. Fortunately, I had two bug cages, and so in he went. Then it was time to go home with the prizes.

When I could get out again, I returned to the field in the day time with the spiders so that they could be properly photographed and then released. The species is Hogna baltimoriana. The female easily had a leg span of about 3 inches, while the skinny male was much smaller:

Bringing up the rear are male and female jumping spiders (Phidippus clarus) that are in an endearing and committed relationship. The male is in plain view, while the female is seen as a vague outline in her silken retreat. According to BugGuide, females of this species are frequently seen hanging out at the top of plants like this. The male, having found her, is now guarding his “intended” against any rival males. Although disturbed by my presence, he would not leave her side:

Readers’ wildlife photos

December 20, 2022 • 8:15 am

Today we have a biology picture story from Athayde Tonhasca Júnior. Athayde’s narrative is indented, and you can enlarge the photos by clicking on them.

To boldly go where no insect has gone before

Athayde Tonhasca Júnior

In April 2016, a birdwatcher on the Dutch coast spotted a buff-tailed bumble bee queen (Bombus terrestris) flying in from the sea. Then another bee, and another, then a wave of bees. Altogether, several hundred bees arrived at the Dutch shore (Fijen, 2020). What probably made the birdwatcher stop watching birds to count bees was the fact that as the bee flies, the nearest land eastwards is England, 160 km across the North Sea.

A buff-tailed bumble bee queen © Holger Casselmann, Wikimedia Commons:

Bumble bees have been observed flying between Estonia and Finland (80 km), England and Jersey (28.4 km), and Skye and the Outer Hebrides (24 km). So to jump from England to The Netherlands is notable, but not implausible. In fact, the seasonal arrival of bumble bee queens along the Dutch coast is not uncommon.

One giant leap for mankind, one small step for bumble bees © Visible Earth, NASA:

We know little about insect dispersal, so the occasional fortuitous observation of their long voyages amazes us. On a moonless night in 2014, a Brazilian hydrographic survey ship sailing the South Atlantic stopped over the Montague seamount to collect samples. Hull and deck lights were turned on to help the crew with their lonely task: they were 389 km from the coast and 764 km from the island of Trindade, with no other vessels nearby. Shortly after the lights were turned on, insects from all directions were flying towards the ship. Most of them collided against the hull and fell into the sea, but researchers on board captured 13 true bugs (Hemiptera), three moths and one dragonfly (Alves et al., 2019). How those insects made it that far into the sea at night and for what purpose, is anybody’s guess.

Montague seamount, anchorage site of the ship Cruzeiro do Sul (20°21′57.60″S, 36°38′46.80″W). ES: Espírito Santo State; RJ: Rio de Janeiro State © Alves et al., 2019.:

Interestingly, bumble bees flying over water bodies are often spotted because they have been following ferries, ships or sailing boats. Nobody knows why they do this: they may be using vessels or their wake as navigation aids. In any case, these observations tell us that bumble bees travel for long distances, which suggests they are migrating.

Strictly speaking, ‘animal migration’ refers to individuals traveling long distances back and forth, like many birds and mammals do. This has never been documented for insects, as no single individual completes the cycle. Instead, insects mate and reproduce along the way or at the end of the outbound journey; only their offspring travel back. But even if done in stages and by different generations, many insects migrate, sometimes in an impressive fashion. The monarch butterfly (Danaus plexippus) can fly non-stop for about 16 h over water at average speeds of 37.5 km/h, and their migratory path extends to almost 5,000 km.

Monarch butterfly migration map © U.S. National Park Service, Wikimedia Commons:

If bumble bees migrate, the consequences are profound. The ability to disperse over long distances would help solve the problem of local shortages of food or nesting sites, or unfavourable changes such as habitat degradation. It would also help bees escape parasites or other enemies. But pulling up stakes may have nothing to do with a rough neighbourhood: it could be a mechanism to increase the genetic diversity of the population.  If a new queen stays around after emergence, she has a good chance of mating with a closely related male.

Whatever the triggers, migration is a powerful survival tactic. It could explain why some bumble bee species seem to persist in hostile, intensively farmed areas. These bees may not in fact survive for long, but their numbers may be replenished periodically by new migrants.

We have just started to understand the travelling plans of our furry pollinators.

Some bumble bees may go on a journey here and there, but the marmalade hover fly (Episyrphus balteatus) is the unbeatable frequent flyer.

If you have taken a stroll in a garden or local park in Europe, you must have seen lots of flies striped orange and black hovering over flowers like tiny helicopters. These are marmalade hover flies (family Syrphidae, aka syrphid flies), which are widespread throughout Europe, North Asia and North Africa.

A female marmalade hover fly © Charles J. Sharp, Wikimedia Commons:

Adults feed on pollen, nectar and honeydew from a range of plants, while the larvae feed on aphids – entomologists say they are aphidophagous. Females locate aphid colonies by their smell and lay their eggs in the middle of them. The larvae hatch immediately, and each one devours up to 300 aphids per day until pupation. So you could say these flying morsels of marmalade are important allies of gardeners and farmers.

Some people will be surprised to know that these fragile insects embark on migrations that may cover thousands of kilometres. Each autumn, marmalade hover flies and other migratory syrphids leave Britain to spend the winter in southern Europe and the Mediterranean. Their offspring move northwards in the spring, lay their eggs, and the new generation sets out the cycle again. To survive these hazardous journeys, hover flies climb to high altitudes, where strong tailwinds take them to their intended destination.

In some years, they travel in large numbers. And ‘large’ is an understatement. By using specialised radar designed for monitoring insects (Vertical-Looking Radars or VLRs), Wotton et al. (2019) estimated that up to four billion marmalade hover flies along with the aptly named migrant hover fly (Eupeodes corollae) cross the English channel to and from Great Britain every year. This represents 80 tons of biomass. If you are impressed by these figures, you should know that hover flies account for only a fraction of insects’ latitudinal migrations known as ‘bioflows’—about 3.5 trillion insects, or 3,200 tons of biomass—migrate into southern Britain annually. Insect bioflows pour vast amounts of nutrients (particularly nitrogen and phosphorus), energy, prey, predators, parasites, herbivores and pollinators into British ecosystems. But we have only a vague understanding of their impact on food webs and local species (bioflows are also hazards to aviation: migrating insects have downed aircrafts).

The marmalade hover fly does not stand out as a particularly efficient pollinator. It is small and not very hairy, a negative mark for a member of the pollinators club because pollen transport depends on abundant body hair. Even still, each marmalade and migrant hover fly carries an average of 10 pollen grains from up to three plant species on their journey into Britain. These are not impressive figures when compared to bees, which return to their nests loaded with pollen. But considering the massive number of flies and the wide range of flowers they visit, a grain of pollen deposited on a flower here and there must add up quickly. The marmalade hover fly is known to improve the yield of strawberries, but we just haven’t paid much attention to these unpretentious pilgrims.

Don’t fly with me, let’s not fly, let’s not fly away

Insects made their first appearance on this planet between 450 and 500 million years ago. But they really took off evolutionarily – and literally – some 80 million years later when they acquired the ability to fly. From then on, insects could explore a three-dimensional world to occupy every nook and cranny of a habitat, escape predators, disperse widely and search for food more efficiently. Insects soon became the dominant creatures on Earth.

A Meganeura monyi fossil, one of the largest recorded flying insects (65-70 cm wingspan) © Didier Descouens, Muséum de Toulouse. Wikipedia Creative Commons:

The ability to fly gave insects so many advantages and opportunities that it may seem inconceivable to give up flight. And yet, many species have done just that. Brachyptery (wing reduction) or aptery (loss of wings) is widespread among insects. It is easy to understand the uselessness or even disadvantage of wings for bedbugs, fleas, lice and other sedentary creatures. But winglessness seems odd for insects we commonly see flying about such as wasps, beetles, and butterflies.

For these insects, wing reduction or wing loss almost always happens to females: males usually retain fully functional wings. The large velvet ant (Mutilla europaea), is a case in point; the male is winged and a capable flier, while the female is apterous, a trait that makes her look like an ant – hence the species’ common name. But in fact this creature is a wasp that parasitizes several species of bumble bees.

A female velvet ant © Tiia Monto, Wikimedia Commons:

The reasons for the loss of flight in insects have baffled scientists for a long time, and Charles Darwin was one of the first to come up with a theory to explain it. Intrigued by the unusual number of apterous beetles on the island of Madeira, Darwin suggested that flightlessness was a survival strategy. To avoid being blown into the ocean by the strong winds that buffet the island year round, the local insect fauna adapted by losing their wings and keeping their feet firmly on the ground.

Darwin’s theory was tested recently by Leihy & Chown (2020) with data gathered from 28 Southern Ocean Islands, a collection of isolated, wind-swept specks of land in the southern regions of the Atlantic, Pacific and Indian oceans. About half of the islands’ indigenous species are unable to fly, which is nearly ten times the global incidence of flightlessness among insects.

Number of flightless (orange) and flying (blue) insect species in the Southern Ocean Islands © Leihy & Chown, 2020:

By analyzing variables such as wind speed, temperature, air pressure, habitat fragmentation, and presence of predators or competitors, the researchers validated Darwin’s hypothesis: wind speed was the main environmental contributor to insect flightlessness. But Darwin didn’t get it quite right: the risk of being blown away is not the main evolutionary driver – after all, even a tiny island is a huge mass of land for an insect. Instead, the enormous energetic cost of flying seems to be the cause.

Indeed, brachypterous or apterous insects are more common in areas where a considerable amount of energy is required for flight such as arctic regions, mountains and deserts; or in stable habitats where dispersal is not vital for survival, such as caves, termite and ant nests, and on vertebrate hosts. Flight muscles comprise 10-20% of an insect’s body weight, and sustained flights consume a great deal of resources. If flying is not significantly advantageous, energy could be spent on some other function – such as laying more eggs, for example.

Egg production explains why winglessness is much more common in females. Free of the costs of flying, a female can produce lots of eggs, which are considerably more expensive energetically than sperm. In fact, the abdomen of many flightless females is greatly enlarged to hold as many eggs as possible. Flight is retained in males probably because it is important for finding females.

In Britain, the belted beauty (Lycia zonaria), the winter moth (Operphthera brumata) and the vapourer moth (Orgyia antiqua) are three of the better-known species with wingless females. The belted beauty is a scarce species confined to coastal areas, but the other two are abundant and widespread; the winter moth is an invasive in North America

A male and a female belted beauty © Harald Süpfle, Wikimedia Commons.

Wings were the morphological feature that assured insects’ success on Earth, but many species made a U-turn in their evolutionary road. For them, flightlessness was the best life strategy. This apparent throwback is another demonstration that evolution is not teleological, that is, it has no objectives or ‘improvement goals’. It just provides the best means for a species to adapt and survive.