Reader’s wildlife tale

June 22, 2022 • 8:00 am

Today we have another combination story and biology lesson from Athayde Tonhasca Júnior, this time recounting how bumblebees can use electricity and the buzzing of their wings to find flowers and effect pollination. Athayde’s tale is indented, and photos, which you can enlarge by clicking, are attributed.

May the Force be with the bee

If we are asked how a bee finds a flower, we think of smells, colours, shapes and textures. These are important sensory signals, but there is another one whose relevance we are beginning to understand: electricity.

The platypus (Ornithorhynchus anatinus), a few fish and amphibians, and some ants, cockroaches, mosquitoes and fruit flies have the ability to detect external electric forces. But vertebrates need water as a conductive medium, while most insects respond only to unusually strong electric fields such as those generated by high voltage power lines. Bumble bees, however, have a sparking story to tell.

Now and then the thunder from a lightning bolt or the shock from a car door jolts us to the realisation that we are components of the Global atmospheric electrical circuit; our world is an immense electric motor. On a calm day, the air is positively charged, while the ground surface and any object connected to it – plants included – have a negative charge. So flowers have a slight negative charge in relation to the air around them. Flying insects experience different physical forces: as a bee buzzes along, electrons are stripped off its body by friction with the air, creating a surplus of positive charges. When the bee approaches a flower, she* attracts the negatively charged pollen grains. The grains stick to the bee, sometimes jumping from the flower even before the bee lands. These electrostatic forces are a great aid to pollination.

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*”She” because a worker honey bee is a sterile female. Apis mellifera sex has some quirks: embryos can develop as males through gene editing; populations of Cape honey bees (Apis mellifera capensis) reproduce without males; and some bacteria such as Wolbachia spp. change the sex of their arthropod hosts, including Hymenoptera (bees, wasps and ants). Nonetheless, their sex is typically binary, just as in Homo sapiens.

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Fig. 1. An electrifying encounter: a positively charged bee approaches a negatively charged flower © Hooven et al., 2019. Molecules 24, 4458.

Fig. 2. Pollen clinging to a bee © Ragesoss, Wikimedia Commons.

But flower power reaches shocking levels for the buff-tailed bumble bee (Bombus terrestris), and probably for other bumble bees as well: they are able to sense the weak electric field around a flower. No one knows exactly how they do it, but mechanoreceptive hairs must be involved. These special hairs are innervated at their base, so they detect mechanical stimuli such as air movement and low frequency sounds. Apparently, the flower’s electrical field moves the mechanoreceptive hairs of an approaching bee, similar to the way a wiped rubber balloon makes your hair stand on end. This hair movement is processed by the bee’s central nervous system and gives information about the shape of the electric field. It works just like Uri Geller’s mystical aura, except that the bee is not a fraud and its powers are not mystical.

Fig. 3. A buff-tailed bumble bee worker with a transponder attached to its back to track it with radar © Meadows, 2012. PLoS Biol 10(9): e1001391.

Fig. 4. Hairs provide thermal insulation, collect pollen and help bees sense air motion, sounds and electricity © Kevin Mackenzie, University of Aberdeen. Attribution 4.0 International (CC BY 4.0).

But bumble bees’ capacity to detect electric forces may go beyond recognising flowers’ sizes and shapes: they could use the information to maximise foraging trips. Once a positively charged bee lands, the flower’s electric field changes and doesn’t go back to normal for about two minutes after the bee leaves. Researchers believe that an altered field warns the next bee that the flower is temporarily depleted of nectar; it’s like turning off a ‘we are open’ neon sign. So the next bee may as well buzz off to another flower with sufficient negative charge and a decent volume of nectar.

Bees and other insects detect ultraviolet and polarized light, and use magnetic fields for navigation. Sensing electricity is one more way their world is experienced differently from ours. And the relationship of bees with physics has other important implications, some of which affect our food supplies.

For most species of flowering plants, fertilization depends on the transfer of pollen from the male anthers of one flower to the female stigma of another. For the majority of those flowers, pollen is released through the splitting open (dehiscence is the technical term for it) of mature anthers. But for approximately 6% of the world’s flowering plants, pollen is kept locked inside non-dehiscent anthers and accessed only through small openings – pores or slits – in their extremities. We refer to them as poricidal anthers.

Fig. 5. Left: stamens, consisting of filaments and anthers. André Karwath, Wikimedia Commons. Most flowers release pollen by the splitting of the anthers along a line of weakness (top right); some only do it through a small hole or pore (bottom right).

Sometimes the whole flower has a poricidal arrangement, as it is the case for the tomato and related plants (Solanum spp.). Pollen is concealed inside a cone-shaped cluster of fused stamens and can only be released though a pore at the tip. Botanist say these flowers have a solanoid shape, after the name of the plant genus.

Fig 6. Solanoid-shaped tomato flowers © Muffet, Wikimedia Commons.

Extracting pollen from poricidal structures is not easy, but some bees know a way to do it.

A bee lands on one of these flowers, bites an anther and curls her body around it. She then lets out bursts of fast contractions and relaxations of her thoracic muscles – those muscles used for flying, but here the wings remain still. The contractions produce cyclical deformations of her thorax that last from fractions of a second to a few seconds: think of a body builder flexing his pectoral muscles really, really fast. These movements generate vibrations that are transmitted to the anther, causing pollen grains to fall though the apical pores and land on the bee’s body, adhering to it with the aid of electrostatic forces.

Fig. 7. A bee engaged in buzz pollination © Bob Peterson, Wikimedia Commons.

This head-banging pollen-harvesting manoeuvre generates a high-pitched buzz, hence it is known as ‘buzz pollination’; or as ‘sonication’ in technical reports. A physicist or an engineer could point out that this mechanism is not strictly sonication because it’s not sound that agitates and extracts pollen, rather the bee’s vibrations on the flower. But ‘sonication’ is the term commonly adopted, so we will keep it. Bumble bees (Bombus spp.), carpenter bees (Xylocopa spp.), and some other bees can buzz pollinate: honey bees (Apis spp.) and most leafcutter bees (Megachile spp.) cannot. And apparently only females know the trick; males have never been recorded buzz pollinating. Watch the whole sequence of events here (buzz pollination from 0:49) and here.

Plants with poricidal floral morphology are distributed across at least 80 angiosperm families, which suggests that buzz pollination has evolved independently many times. This has probably been helped by bees’ readiness to buzz for other reasons such as warning enemies, compacting nest materials, or cooling/warming their nests by beating their wings.

“Buzz-pollination syndrome”, the name given for this plant-bee association, is not just a biological curiosity. It makes a huge difference for crops such as tomatoes, raspberries, cranberries, blueberries, aubergines, kiwis and chili peppers. These plants don’t necessarily need buzz pollination to reproduce, but they produce more and better fruit if they are buzzed because more pollen is transferred and more ovules are fertilised.

In the late 1980s, Belgian and Dutch companies developed techniques to rear at a large scale the buff-tailed bumble bee, the ultimate buzz pollinator. Local producers of greenhouse tomatoes began replacing costly mechanical pollinators with boxes containing bumble bee hives, and a global, multi-million pound industry was born. Today, all ordinary tomatoes bought in a European supermarket have matured with the help of commercially reared bumble bees (they also transmit diseases to wild bees, but that’s a story for another time).

Fig. 8. A commercial bumble bee hive used in greenhouses © Elaine Evans, The Sustainable Agriculture Research and Education.

We may see pollination as a harmonious relationship where plant and insect go out of their way to help each other, but this is mistakenly romantic. A bee aims to take all the flower’s pollen: pollination happens because a few grains are dropped or rubbed off by accident. And a plant produces as little nectar and pollen as necessary to entice a flower visit. So the association between pollinators and flowers is best described as a mutual exploitation.

Buzz pollination fits nicely into this scenario. Poricidal anthers prevent excessive pollen expenditure by rewarding only a few specialist pollen gatherers, which increases the chance of pollination. Plants with poricidal structures typically secrete little or no nectar but their pollen is rich in protein, which convinces a bee to go to the trouble of buzzing to gain a small dose of the yellow stuff. It’s a clever and efficient trade agreement in the pollinators’ world.

Readers’ wildlife photos and stories

June 6, 2022 • 8:00 am

Today we have another photo-and-story tale by reader Athayde Tonhasca Júnior, this time about amazing ways that flowers have evolved to reproduce by taking advantage of insects. His tale of pollination is indented, as are the pictures (not his, but credited). You can enlarge the photos by clicking on them:

‘You WILL pollinate me!‘: pushy characters of the plant world

When an insect visits a flower, some pollen grains become accidentally attached to its body. The insect moves on and some of the pollen is transferred to the stigma (the part that’s receptive to pollen) of another flower, kicking off the process of plant reproduction.

Fig. 1. A typical flower:

Such a passive, leave-it-to-chance approach is not good enough for some plants. Evolutionarily speaking, they have taken the matter into their own hands by forcing pollen onto visitors.

The mountain laurel (Kalmia latifolia) is a perennial shrub native to the eastern United States and well known on the other side of the Atlantic as an ornamental. The anthers of the mountain laurel flower are attached to small pouches on each petal. As the flower matures, the petals curve backwards, pulling on the stamen filaments, which bend under tension.

Fig. 2. A mountain laurel flower with eight of its ten anthers inserted into pockets in the corolla and held under tension © Derek Ramsey, Wikipedia:

When a relatively large insect such as a bumble bee lands on the flower, it may trip on a filament, releasing the anther from its pocket and launching pollen into the air at great speed. As most of the pollen is flung towards the centre of the flower, researchers believe this catapult apparatus results in more pollen grains attached to bees.

Alfalfa or lucerne (Medicago sativa) has a similar mechanism: its stamen filaments are stuck together into a structure called a ‘sexual column’, which is held under pressure inside two bottom keel petals that are fused together. When a bee pushes on these petals, the column is released, springing upwards and slamming into the upper petals. This process is called ‘tripping the flower.’ When it happens, pollen falls on the flower’s female reproductive organ and also on the bee, which then moves on to another flower. Some bees such as the European honey bee (Apis mellifera) don’t appreciate being whacked by a plant, so they avoid alfalfa or learn to get to the nectar without tripping the flower. Farmers can’t count on finicky honey bees, so they rely instead on the alfalfa leafcutter bee (Megachille rodundata) because this species is not bothered by a slap or two. Follow the whole story in this video (flower tripping from 2:20).

Fig. 3. A bee visits an alfalfa flower, tripping it © Diana Sammataro, Sustainable Agriculture Research and Education:

The tricks performed by the mountain laurel and alfalfa are known as explosive pollen release, and similar devices have evolved in plants from several families. Insects are not always involved: sometimes plants rely on explosive pollination to launch pollen into the air so that it can disperse long distances and, with luck, drift towards a receptive flower.

Flower tripping is an ingenious mechanism, but it pales in comparison to the stratagem employed by Neotropical orchids in the genus Catasetum. These plants awed and puzzled Charles Darwin: ‘I have reserved for separate description one sub-family of the Vandeae, namely the Catasetidae, which may, I think, be considered as the most remarkable of all Orchids.’ (On the Various Contrivances by Which British and Foreign Orchids Are Fertilised by Insects, and on the Good Effects of Intercrossing, 1862).

Catasetum orchids are dioecious (either male or female) and display strong sexual dimorphism, that is, flowers of both sexes look different: so much so that male and female plants were once thought to be separate species. These flowers produce no nectar, but they secrete fragrances that are collected by male orchid bees (tribe Euglossini), possibly to use for attracting females: we don’t know for sure.

Fig. 4. Male (L) and female Catasetum arietinum inflorescences © Brandt et al., 2020. AoB PLANTS 12(4).

Fig. 5. Male (top) and female Catasetum arietinum flowers © Brandt et al., 2020. AoB PLANTS 12(4).

When a male orchid bee lands on a male Catasetum flower, it touches a pair of antennae-like structures that trigger the shooting of a sticky pollen blob known as pollinium against the unsuspecting visitor. It happens with such force that the poor bee is sometimes knocked off the flower. Watch the stunning (literally) speed of pollinium ejection here, which can reach 2.6 m/s. For comparison, a pit viper, another denizen of Neotropical forests, strikes at 1.6 m/s. We don’t know how the orchid does it, but apparently changes in electrical potential and tissue turgor are involved, similar to what happens with the sensitive plant (Mimosa pudica). Incidentally, Darwin never observed Catasetum flowers in the wild, but he reasoned that pollen ejection must be related to bee pollination.

Fig. 6. A male orchid bee © Alejandro Santillana, Insects Unlocked, Wikipedia:

The male bee is not only surprised, but ends up with a hefty load as well: a pollinium can make up 23% of its body weight. He does not like this rough treatment one bit, so he may avoid a male flower on the next visit and go instead for a female flower, which does not have a pollen-spitting attitude. That suits the orchid just fine: the switch increases the chances of the pollinium lodging itself in a specialised receptacle of the female flower, fertilising it.

Fig. 7. A male Eufriesea auriceps carrying a pollinium (indicated by the arrow) of Catasetum fimbriatum © Reposi et al., 2021. Protoplasma 258(5):

Some plants go beyond hurling pollen at unsuspecting visitors: they resort to coercive control.

In ancient Greece, nymphs were deities portrayed as gorgeous maidens who would hang around ponds, rivers and other outdoor spots. But their beauty was hazardous: just like those wicked mermaids, nymphs could lure a virtuous man who happened to be passing by, leading him to madness or perdition.

Fig. 8. Naiads (freshwater nymphs) abducting the Greek hero Hylas © John William Waterhouse, 1896:

Nymphs may have been the product of overstimulated male fancy, but they also inspired the name of the water lily plant family, Nymphaeaceae. And just like the Greek nymphs, some water lilies do engage in devious charming, sometimes with fatal outcomes.

The white water lily or fragrant water lily (Nymphaea odorata) is an aquatic plant from shallow lakes, ponds, and slow moving waters throughout the Americas. It’s a popular nursery choice for ornamental ponds and water gardens around the world, but its floating leaves can form thick mats of vegetation, sometimes preventing light penetration and retarding water flow. So this plant is considered invasive in some places.

When a white water lily flower opens, its female parts are shaped like a bowl with the stigma at the bottom. This bowl is surrounded by a wall of stamens and filled with a viscous liquid full of sugars and detergent-like substances (surfactants). If this rigging has the look of a trap, that’s because it is one.

Fig. 9. A white water lily flower © SanctuaryX, Wikipedia:

The fragrant flower – hence the epithet odorata – is irresistible to bees, flies and beetles. When a visitor lands, it falls into the bowl. It tries to pull itself out, but the slippery soup and the palisade of flexible stamens hinders escape. As the insect struggles, pollen attached to its body is washed off by the liquid. The pollen drifts to the bottom of the bowl where it comes into contact with the receptive stigma, pollinating the flower. The insect may eventually crawl out, or it may drown: it makes no difference to the white water lily. It’s got its pollen.

At the end of first day of blooming, the flower closes. When it opens again the next day, the stigma is no longer receptive and no fluid is produced, so visiting insects are spared a watery end. Instead, they can fly away covered with pollen if they drop by on the second or third day of blooming, when the stamens release the powdery stuff. This stigma-stamen asynchrony prevents self-fertilization. On the fourth day, the flower is pulled underwater, where the seeds mature.

Fig. 10. Sweat bees (family Halictidae) are common visitors to white water lilies © Wikipedia:

In South America, giant water lilies (Victoria spp.) take unlawful detention to another level. Their flowers attract and trap beetles until the following day, when they are allowed to leave loaded with pollen. Watch a time-lapse video of a giant water lily flower opening and closing over the course of two days. The flower opens during the receptive stigma phase, closes to entrap beetles, turns pink (pollen release phase), opens again to free its pollinators, then closes before sinking in the water.

By detaining insects temporarily, plants increase the probability of fertilization. This type of relationship is known as entrapment pollination, and molecular studies suggest this is one of the oldest pollination systems. Nymphaeales (the order consisting of water lilies and other plants) and beetles have been playing this game for approximately 90 million years. It has worked nicely for both gaolers and gaoled.

Readers’ wildlife tales

May 25, 2022 • 8:00 am

Today’s bit of enlightenment comes from Athayde Tonhasca Júnior, and is on a subject that makes some people squeamish. But read on!

‘Thick-headed undertakers in the night of the living dead’

If you watched Alien, you may have jumped out of your seat when the baby monster burst from the astronaut’s chest. But an entomologist may have nodded knowingly: ‘Ah, a human parasitoid!’ Indeed, the screenwriters acknowledged entomological inspirations for coming up with the alien’s life cycle.

Here on Earth, a parasitoid is an insect whose larva develops inside the body of a host (usually another insect), eventually killing it. This type of life history lies between a predator’s and a parasite’s: a predator such as a dragonfly takes several prey and kills them outright, while parasites such as lice, fleas and ticks live off hosts without killing them.

Wasps account for most parasitoid species, but quite a few of them are flies. These include the 800 or so species of thick-headed flies (family Conopidae). A look at one of them explains their common name, although some species look more like wasps or bees than flies. They are also known as bee-grabbers or conopids.

Fig. 1. A conopid fly © Fir0002, Wikipedia.

Thick-headed flies hang around flowers looking for a sip of nectar. But a female may have other ideas: she may be waiting for an opportunity to lay her eggs, which is bad news for a bee or wasp.

It goes like this: an unsuspecting bumble bee worker approaches a flower. A female conopid closes in and grabs the bee in mid-air. Still afloat, she pries open the bumble bee’s abdominal segments with her theca, which is a pad-like, hardened structure at the end of her abdomen. Sometimes attacker and victim fall to the ground, but the outcome is the same; the female fly lays a single egg inside the bumble bee and lets it go.

Fig 2. A female conopid with her menacing theca clearly visible © Hectonichus, Wikipedia.

The drama is over within seconds, and both insects fly away. The fly will stalk another quarry. But the bumble bee is done for.

The egg hatches and the conopid larva develops inside the bumble bee, consuming her innards. But the larva does not penetrate the host’s thorax, thus leaving her flight muscles intact. The bee carries on with her life, feeding and taking nectar back to her nest, although less and less efficiently as the parasitoid grows. Within 10 to 12 days her abdomen is completely taken up by the larva, which has nothing more to eat. The bee dies and falls to the ground (if you find a dead bumble bee with a swollen abdomen, conopid parasitism could be the causa mortis). The larva pupates and overwinters inside the bee’s body, and the adult emerges in the following year.

Fig. 3. A conopid puparium inside the abdomen of a Centris analis bee © Moure-Oliveira et al., 2019. The Science of Nature 106. 10.1007/s00114-019-1634-9.

Some conopids increase the chances of their pupae making it through the winter with a trick that may seem macabre to human eyes: they induce their bumblebee hosts to dig their own graves. In North America, bumblebees parasitized by the conopid Physocephala tibialis bury themselves in the ground just before popping the clogs. This grave-digging behaviour does not make a difference for the bee, but the parasitoid pupa is sheltered from cold and dehydration during winter months, and less exposed to pathogens and its own parasites. Hibernation in the soil also promotes larger and healthier adult flies.

Fig. 4. The grave-digging inducer Physocephala tibialis © Beatriz Moisset, Wikipedia.

But bees don’t take it lying down. When parasitism pressure becomes too high, some species reproduce later in the year to avoid peaks of conopid populations. And some bumblebees – like many other insects – secrete melanin, which encapsulates and suffocates internal parasites. It is estimated that melanisation kills up to 30% of conopid larvae.

Fig. 5. A larva with encapsulated wasp eggs © Nathan T. Mortimer, Illinois State University.

After a parasitized bumblebee has dug its burial pit somewhere in America, a cold, drizzly night falls over the land. All is quiet. Until in an apiary nearby, one of the resident honey bees (Apis mellifera) does something odd: she emerges from the hive and flies towards a streetlight glowing faintly in the distance. A few of her sisters follow suit, although some of them fall to the ground and begin walking around in circles, apparently confused. None of these night wanderers will ever return to the hive; soon they will all be dead. They have been victims of a parasitoid ominously named the zombie fly (Apocephalus borealis).

Fig. 6. A female zombie fly © Core et al., 2012. PLoS One 7(1): e29639.

This fly belongs to one of the largest insect groups, the family Phoridae. They comprise about 4,000 described species, but specialists believe this number represents a fraction of the total. Phorids look like fruit flies with arched backs, and when spooked they run away before taking flight. Such behaviours explain their common names: hump-backed flies or scuttle flies. They are everywhere, and have a variety of feeding habits such as saprophagy (they eat decaying organic matter), predation, and herbivory. One species is a serious pest of cultivated mushrooms.

Two groups of Phorid flies, the genera Pseudacteon and Apocephalus, are found mostly in South America and are charmingly known as ant-decapitating flies. A typical species approaches an ant from behind and uses its powerful, hooked ovipositor to inject an egg in the victim’s head or thorax.

Fig. 7. The hooked ovipositor of Pseudacteon curvatus, a decapitating fly © Sanford Porter, Wikipedia.

The resulting larva moves to the ant’s head, where it feeds on hemolymph (‘blood’) and tissues. Eventually, the larva consumes all the head’s contents, causing the ant to wander around erratically. In two to four weeks, the larva is ready to pupate. It releases enzymes that dissolve the tissues attaching the ant’s head to its body. The head falls off, and the fly pupates inside it before emerging as an adult. These flies are efficient ant killers, and therefore are promising biological control agents against invasive species such as fire ants (Solenopsis spp.).

Fig. 8. A) An ant-decapitating fly (Pseudacteon sp.) preparing to inject an egg into the thorax of a fire ant. B) A decapitated ant with a fly maggot consuming the contents of its head © Porter & Gilbert, 2005. International Symposium on Biological Control of Arthropods.

The zombie fly does not decapitate honey bees, but much of its life history is similar to those of its tropical relatives. It lays its eggs in the abdomen of the bee. The larvae feed on hemolymph and flight muscles, and when they are done, they leave the host to pupate outside. Up to 13 larvae have been observed coming out of a dead honey bee.

Fig. 9. A zombie fly ovipositing into the abdomen of a honey bee worker © Core et al., 2012. PLoS One 7(1): e29639.

Fig. 10. Two fly larvae leaving the host at the junction of the head and thorax © Core et al., 2012. PLoS One 7(1): e29639.

We don’t know why a parasitized honey bee abandons her nest, especially at night, to wander on a suicidal excursion. Her neurological wiring may have been highjacked by the fly, inducing the bee to seek a safer place for the development of the parasitoid’s eggs and larvae. The bee may have been forced out by her healthy sisters; or she left the colony on her own, acting on an altruistic instinct to avoid an epidemic.

Fig. 11. Four zombie fly pupae surrounding the dead honey bee from which they emerged © John Hafernik, University of Florida Entomology and Nematology Department.

The zombie fly is native to North America, where it has long been known to parasitize bumble bees and wasps. Then in 2009, there was an alarming discovery: the fly was also attacking honey bees in parts of the country. And there was more bad news to come. The zombie fly harbours the fungus Nosema ceranae and the Deformed Wing Virus, which are serious threats to honey bees. Researchers don’t know yet whether the zombie fly plays a role in the transmission of those pathogens to bees, but the possibility is worrying.

Conopids and zombie flies are some of the many parasites and parasitoids capable of changing hosts’ behaviour for their own benefit. Some wasps turn ladybirds into paralysed living shields over their eggs, and some fungi make ants climb up plants so they can release spores into the air. Perhaps the most notorious case is the effect of toxoplasmosis cells on rats and mice. Infected rodents become attracted to cat’s urine and are less likely to hide. This altered behaviour is a death wish: they became easy prey for cats, in which toxoplasmosis cells complete their development. Carl Zimmer discussed many other examples in his excellent Parasite Rex; you can read about some of them here.

Parasitism seems gruesome and cruel. Even Darwin was dismayed by it, as he expressed in one of his letters: ‘I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ [ a group of parasitic wasps] with the express intention of their feeding within the living bodies of caterpillars.’* But such anthropomorphism is misguided and biased. Parasitoids, predators and parasites are regulators of the natural world: about 10% of all known insect species are parasitoids, although specialists believe this figure is a huge underestimation. They prevent excessive population growth, including of agricultural pests and disease vectors. Parasitism helps shape biodiversity and ecosystems, so it is not intrinsically bad or good. It is a characteristic of life on our planet.

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* This famous quotation inspired a team of ichneumonid specialists to propose in 2019 ‘Darwin wasps’ as a vernacular name for this group of insects, so that they may become better known and appreciated.

Fig. 12. A Darwin wasp © Charles J. Sharp, Wikipedia.

How Asian honeybees kill their fearsome hornet predators

May 10, 2022 • 12:45 pm

I can’t remember why I opened the natural-selection chapter in Why Evolution is True (chapter 5: “The Engine of Evolution”) with the story of the Asian giant hornet (Vespa mandarina) and of the counterdefense of its prey of native honeybees. (The European honeybee, more recently introduced into Asia, has not evolved such a bizarre and amazing defense.)  The giant hornet is much to be feared by both honeybees and humans: it’s as big as your thumb, and several humans (and millions of bees) die from its attacks every year.

Since you all should have a copy of WEIT (as Hitch would say, “Available at fine bookstores everywhere”), I won’t recount the story of the native honeybees’ defense, but it involve luring the voracious hornet scout into the bee nest and the cooking it to death:  surrounding it with a ball of vibrating bee bodies that raises the ball’s internal temperature to 117 degrees F (47°C): a temperature that kills the wasp but not the bees.

I suppose I put that story in because it’s a stunning example of the power of natural selection to shape behavior (in both wasp and bee), and not many people knew about it. Now I hear that a lot of readers especially liked that story. It is a true one, and in this segment from BBC Earth, you can see the nefarious hornet scout discovering a hive of native honeybees.

The scout marks the hive with pheromones and usually flies back to recruit a swarm of fellow hornets to return to the nest to destroy it: a process that can take only a short while as the wasps  nest in minutes, decapitate adult bees and steal their honey and and bee grubs. But, as I relate in the book, sometimes, as here, the hornet scout never gets back to its own nest because of the counterdefense. The native bees lure it inside and cover it with vibrating bees that kill it.

This video is, of course, far more vivid that what I could say in words, so I want to show it here. But imagine the sequence of evolutionary steps that produced this defense!

If you want to see how these hornets slaughter the non-native European honeybees, watch this gruesome attack (each wasp can kill 40 bees per minute!). I’m sure I’ve shown this video somewhere in the distant past.

Now if you’ll excuse me, i’ll go home to rest.

Readers’ wildlife stories (and tales)

May 7, 2022 • 10:00 am

Today’s wildlife contribution is another absorbing photo-themed story by Athayde Tonhasca Junior. His tale is indented, and you can enlarge the photos by clicking on them.

According to the Woke canon, practically every scourge of humanity – poverty, colonialism, inequality, racism, global warming – is the work of prostate-bearing people, particularly the white variety. But Homo sapiens is not alone: the European honey bee (Apis mellifera) and the wool carder bee (Anthidium manicatum) have also been indicted for the sin of male toxicity.

As bad raps go, the one earned by honey bee males (drones) is hard to beat. Known as freeloading loafers whose single purpose in life is to copulate, they have been tagged with the unflattering ‘flying sperm’, and called ‘lazy Willies’ by the Germans. Even Shakespeare vilified ‘The lazy yawning drone’ (Henry V).

But the Bard and others were too quick to judge.

Researchers have not given male bees much attention because of their reputation as secondary players. But we do know that drones are fundamental for the workings of a bee colony by producing body heat that helps maintain the temperature of the hive. Honey bees do not overwinter, so thermogenesis (heat production) is a life or death matter for the colony. Because drones are bigger and stronger than female workers, their contribution is disproportionately higher.

Whatever input drones may have in the functioning of a colony, all are dramatically and fatally surpassed when they reach sexual maturity. On a warm and sunny day during the mating season, drones fly out to meet their mates from the neighbourhood 10 to 40 m above ground. These clouds of bachelor bees can be thousands strong. After all available males have gathered, virgin queens leave their hives and join in: love is in the air.

Fig. 1. A honey bee drone © Waugsberg, Wikimedia Commons.

Thanks to its big eyes, a drone spots a queen in the melee, zeroes in and grabs her. Mating is completed in less than five seconds, during which the drone’s endophallus (a penis equivalent) is turned inside out into the queen and inflated by haemolymph (‘blood’) under high pressure. As haemolymph rushes into his endophallus, the drone loses control of his body and falls back, unable to move. Ejaculation happens at such speed and force that it can be heard by people as a popping sound.

Alas, these amorous exertions cannot end well for the lucky suitor. His endophallus breaks off, leaving its extremity inside the queen. The drone drops to the ground and dies shortly after. You can watch a dramatization of the event in this video:.

Fig. 2. A honey bee’s everted endophallus © Michael L. Smith, Wikipedia Commons.

However, his anatomical sacrifice does not guarantee sole paternity. Another drone may remove the piece of endophallus from the queen and mate with her, and the process may be repeated with up to 20 successive drones.

Fig. 3. Semen being collected from a drone for a honey bee germplasm collection © USDA.

Collecting semen from a drone honey bee that will be used to artificially inseminate a queen bee.

Life has more misfortune in store for our drones. They have a grandfather and grandsons, but not a father or sons. Such surreal family settings come about because of haplodiploidy. This tongue-twister refers to a reproductive system where females have two sets of chromosomes (just like us), but males have only one. After mating, a queen bee stores sperm in an internal sac called spermatheca. She may release some of the sperm when an egg passes down her oviduct, in which case the egg is fertilized and generates a female with two sets of chromosomes. If no sperm is released from the spermatheca, the egg will produce a male with a single set of chromosomes inherited from the queen: there is no genetic input from daddy. Sex is determined in a similar way for all Hymenoptera (bees, ants, and wasps), Thysanoptera (thrips) and a few other insects.

The consequences of haplodiploidy are profound. Human offspring share 50% of their genes with their mothers and 50% with their fathers, so siblings share on average 50% of their genetic material: (50% + 50%)/2. Female honey bees however share 50% of their mother’s genes, but all of their father’s. So they are related by (50%+100%)/2, which is 75%. You can find a detailed explanation of these calculations here. [JAC: this assumes that the female is inseminated only once.]

This 75% helps solve Darwin’s ‘one special difficulty’ which he stumbled upon when writing On the Origin of Species. Almost all bees, ants and wasps in a colony are sterile workers whose function is to gather food, protect the nest and help the queen lay eggs; they do not reproduce therefore are not subject to natural selection. How could these social insects evolve?

The answer to Darwin’s conundrum is kin selection: because sister bees are more related to each other than they are to the queen or any possible daughters, they have a better chance to pass on their genes by helping their mother produce more sisters, rather than by reproducing themselves. The theory of kin selection involves self-sacrificial behaviour and altruism, and because it is supposed to be applicable to us, naturally it has been controversial and debated for years.

While these drone shenanigans take place in an apiary, in a garden nearby a bumble bee wavers lazily over a patch of lamb’s ear (Stachys byzantina), as if considering whether its flowers are worth a visit. Before the bee makes up its mind, out of nowhere a black and yellow projectile collides mightily against it. The stunned bee falters and dips in the air, and is hit again. Struggling to stay aloft, it turns around and flees as fast as its battered wings allow it. If the poor bee could glance back, it would spot the aggressor now turning its attention to an unsuspecting honey bee.

The bumble bee and honey bee had the misfortune of invading wool carder bee territory. Males of this species are notoriously aggressive towards perceived threats, either other males or any bee that may have an eye for plants from which female wool carder bees collect pollen, nectar or nesting materials.

Fig. 4. A male wool carder bee © Bruce Marlin, Wikipedia Commons.

Male wool carder bees are all ruthless determination. Witnesses have reported five bees knocked down in quick succession, bumble bees and honey bees with their wings torn apart, victims thrown to the ground and mauled by bites and strikes from the attacker’s abdominal spines. Two males have been observed hovering face to face like stags readying for battle. When they clashed, the smaller bee fell to the ground, wings outstretched and abdomen vibrating (presumably dying or limping away afterwards).

Fig. 5. Details of a male’s menacing abdominal spines © Soebe, Wikipedia Commons.

Such Rambo-like aggressiveness has biological causes: polyandry and a physiological quirk known as ‘last male sperm precedence’. Polyandry – from the Greek for ‘many husbands’ – describes when a female mates with several males in a breeding season. This mating system is uncommon among bees; for most species, females copulate once with a single male. But wool carder bees are polyandrous, just like honey bees: monogamy is not an option. Last male sperm precedence happens when the male copulating last in a sequence of partners has a better chance of fertilising the female. So to assure paternity, a male must fend off potential competitors and do as much mating as possible with any female in his territory: as often as every six minutes. This short film follows the exploits of a male wool carder bee (warning: contains scenes of sex and violence).

But for the female, life is not all harassment from an aggressive Lothario: thanks to her guardian, she has a patch of pollen and nectar all for herself, free of competitors. She can focus on feeding and building her nest, which celebrated naturalist and entomologist Jean-Henri Fabre (1823-1915) considered ‘quite the most elegant specimen of entomological nest building’. She begins by stripping the fuzz from the leaves and stems of lamb’s ear and related plants such as mint, deadnettle and sage (family Lamiaceae). This material is rolled into a ball – watch her do it – an operation akin to ‘carding’, the process of separating wool threads for the production of cloth:

Fig. 6. A carding machine. Wikiwand.

SMARTEST CONSULTANTS

Fig. 7. A female wool carder bee collecting nesting material from lamb’s ear © Ilona Loser, Wikipedia Commons.

The female will carry this bundle to a pre-selected cavity such as a hole in dead wood, a crevice in the mortar joints of a wall, or a hollowed plant stem. Once inside the nest, she will shape the collected fibres into a cell in which she will lay an egg and deposit a mass of nectar and pollen to provide for the larva. She will build several cells in a single cavity, then seal up the entrance.

Fig. 8. Rendition of a wool carder bee life stages. From left to right: pupa, larva, egg, and adult (female). © Samantha Gallagher, University of Florida Featured Creatures.

This bee has a Palearctic origin (Europe, Asia and North Africa), but was accidentally introduced to north-western USA is 1963. From there, it has dispersed throughout the country and the Americas all the way to Uruguay. It is spreading in Britain too: once confined to southern England, it was recorded in Edinburgh in 2011.

So while modern mores have destined macho H. sapiens to extinction, for A. mellifera and A. manicatum it’s raining males, hallelujah!

Readers’ wildlife photos and stories: the entomology behind Lyle’s Black Treacle

April 22, 2022 • 9:30 am

Today we have another history/natural history/general interest contribution from reader Athayde Tonhasca Junior. His notes are indented, and click on the photos to enlarge them.

If you walk into a British supermarket and pick up a tin of Lyle’s Golden Syrup or Black Treacle (these are by-products of sugar refining processes, similar to corn syrup and molasses), you will notice one of the strangest logos for a food product: a dead lion surrounded by a swarm of bees above the slogan ‘Out of the strong came forth sweetness’.

Lyle’s Black Treacle:

The image and text are based on the Biblical tale in which Samson kills a lion to find a honeycomb inside it. This unexpected discovery led Samson to write a riddle: ‘Out of the eater came forth meat and out of the strong came forth sweetness’. Meaning: from the carcass of a lion (the eater and the strong), Samson had meat and honey (sweetness). The story impressed the staunch Presbyterian Abram Lyle (1820-1891), businessman and founder of the sugar refinery Abram Lyle & Sons. And so one of Britain’s oldest brands was born: the logo hasn’t changed much since 1885.

But the yarn about dead animals and bees is older than Samson’s adventure. The Greeks, the Romans and other Mediterranean peoples believed that honey bees originated spontaneously from animal carcasses, primarily of oxen. The Greeks had a name for this miracle: bugonia, from bous (ox) and gon (generation). The Roman poet Virgil (70-19 BC) told the story of a farmer, who in want of bees, slaughtered an ox and waited for a new swarm. Bugonia inspired Shakespeare as well: ‘Tis seldom when the bee doth leave her comb, in the dead carrion’ (Henry IV).

Bugonia, unknown author, 1517:

But the belief in carcass apiculture suffered a fatal blow in 1668, when the Italian physician, naturalist, biologist and poet Francesco Redi (1626-1697) published Esperienze Intorno alla Generazione degl’Insetti (Experiments on the generation of insects). By comparing covered and uncovered meat-filled glass containers and observing the presence or absence of flies and maggots, Redi put an end to the idea of spontaneous generation.

Bugonia was dead, but the recurrent reports of bees swarming around carcasses, just like in Lyle’s logo, still required explanation. Enter diplomat and entomologist Baron Karl-Robert von Osten-Sacken (1828-1906), who, despite his Teutonic name, was Russian. The Baron suggested that the ‘bees’ found around dead animals were in fact flies: not the expected carrion-seeking blow flies and blue bottles, but the drone fly, Eristalis tenax.

The name ‘drone fly’ comes from its resemblance, in appearance and behaviour, to honey bees. The adults feed on pollen, especially from yellow flowers such as dandelions, and are known to pollinate various crops. The larva has a long ‘tail’, which is a specialized respiratory structure that works as a snorkel, allowing the insect to breathe air from the surface when submerged in liquids. This respiratory appendage gives the larva its common name: the rat-tailed maggot.

A male drone fly. Like many fly species, males have larger eyes that almost touch, while female eyes are spaced apart © Sandy Rae, Wikimedia Commons.

A drone fly larva, or rat-tailed maggot © Obsidian Soul, Wikimedia Commons.

In his 1894 publication ‘On the oxen-born bees of the Ancients (bugonia) and their relation to Eristalis tenax, a two-winged insect’, von Osten-Sacken explained the bugonia phenomenon as this: ‘The original cause of this delusion lies in the fact that a very common fly, scientifically called Eristalis tenax (popularly the drone-fly), lays its eggs upon carcasses of animals, that its larvae develop in the putrescent mass, and finally change into a swarm of flies which, in their shape, hairy clothing and colour, look exactly like bees, although they belong to a totally different order of insects.’

The Baron was close: the female drone fly does not lay her eggs on carcasses, but on the exudates and foul water accumulated around them. Other contaminated water sources would do, such as sewage, manure lagoons, holding pits in livestock areas, ditches and wet silage.

Hence an entomological/historical mystery may have been solved.

Drone flies are not the only insects interested in a dead lion: blow flies of the genus Lucilia may get to it first – or to a dead bird or small mammal in your neighbourhood. You will certainly have seen these shiny, metallic green flies, known as green bottles, in your garden or around your bins. They comprise several species that are difficult to tell apart.

A female green bottle fly.

Female green bottle flies use their powerful sense of smell to track minute volumes of sulphur volatiles released by recently deceased animals. Once a fly finds a corpse, sometimes within minutes of death, she lays 150 to 200 eggs on it. The eggs quickly hatch into maggots, which feed on the rotting flesh. After about ten days, they leave the body and pupate in the soil nearby.

Gross, you say? Well, green bottle flies help decompose carcasses, accelerating the release of organic matter and nutrients into the ecosystem. Without them and other scavenging insects such as flesh flies and carrion beetles, decomposition by microorganisms would take much longer, and rotting carcasses would accumulate in the landscape. Alas, these flies can lay their eggs on live bodies as well. The common green bottle fly Lucillia sericata is a serious pest of sheep, causing significant expenses for farmers.

However, green bottle flies are not all death and pestilence. Because their maggots preferentially consume dead tissue, they have been used for the treatment of non-healing wounds in people and animals. Maggot therapy has been known since 1557 when Ambroise Paré (c. 1510-1590), the Chief Surgeon of King Charles IX of France, described a soldier with a deep head wound filled with a ‘great number of worms’, and noted that the patient ‘recovered beyond all men’s expectation’. This unusual but effective treatment saved many lives before antibiotics become widely available, and the therapy is experiencing a comeback because of antibiotic resistance. Disinfected L. sericata maggots are placed in a diabetic ulcer, bedsore or other chronic wound, where they eat the necrotic tissue and produce antimicrobial enzymes that prevent infections, thus speeding the growth of new tissue.

Maggot debridement (the removal of necrotic tissue to help a wound heal) on a diabetic foot © Alexsey Nosenko/Maggot Medicine, Wikimedia Commons

Wound healing is not the only service provided by L. sericata. This species is a good pollinator of crops that produce few flowers or little pollen such as cauliflower, cabbage, lettuce, carrot, onion, leek, and asparagus; so much so that this fly is commercially available to complement the pollination by bees in glasshouses. Not so bad for those green creatures buzzing around your rubbish!

Because drone flies and green bottles are dependent on dead bodies, they are important aids to forensic science. By noting the flies’ life stage, criminal investigators can determine a person’s time of death, and the presence or absence of flies in certain environments can be an indication of tampering with the body: drone flies for example are indicators of partially submerged cadavers.

Forensic entomology students learning the ropes © UC Riverside.

Shortly after an animal expires, its body starts releasing the scents of decay. Thanks to their sensitive antennae, sexton beetles such as Nicrophorus vespilloides can locate a corpse within an hour of death and from as far away as 3 km. The first male-female pair to arrive examines it to assess its size; bodies too big to be handled are rejected. If the ground is unsuitable for digging, they drag the body to a better location, all the while fencing off late arrivals and competitors.

A common sexton beetle, Nicrophorus vespilloides © Holger Gröschl, Wikimedia Commons.

The beetles loosen the soil with their heads and shove it aside, gradually constructing a burial chamber that eventually sinks the carcass into the ground, a process that may take up to 8 hours. After burial, the beetles strip away any fur or feathers and shape the flesh into a compact ball, dousing it with secretions that act as anti-bacterial agents to slow down decomposition. The female then lays her eggs in the soil nearby. Watch sexton beetles in action here and here.

Two common sexton beetles in a dead rodent caught in a mousetrap © Calle Eklund, Wikimedia Commons.

Until they are about three days old, sexton beetle larvae beg for food by pressing against the adult’s jaws, which stimulates regurgitation – a behaviour normally associated with birds and their nestlings. Afterwards the larvae feed directly on the carcass, but they are cared for by their parents throughout their development. This is a rare and highly developed behaviour in insects, normally found in social bees, wasps, ants, and termites. But it’s not all love and care in the life of a young sexton beetle; if the adults sense that the brood is too big or the carcass is too small, some of the smaller larvae are eaten, so that the remaining ones will have a sufficient food supply.

A female N. vespilloides feeds her begging young © Allen J. Moore, Nature Communications 6: 8449.

These complex interactions between parents and offspring represent the highest degree of sociality among Coleoptera, and that’s why sexton beetles are considered to have attained the level of ‘subsocial’ on insects’ sociality spectrum. And recently, a new twist has been revealed in their intricate lives.

A female dedicates her time and energy to the offspring. The male however may have other ideas thanks to sexual competition; he may be driven to pester her for sex to guarantee paternity because given the chance, other males will have a go with the busy female. She has a chemical solution for this harassment problem: during early stages of larval growth, she releases methyl geranate, which has anti-aphrodisiac properties and inhibits the mating instinct of males.

So there you have it: sexton beetles have created the first anti-Viagra.

If you bump into a dead lion or another cadaver, you may pause to brood over life and mortality. But although that carcass was the end of the line for one life, by no means was it the end of the line for life. Dead animals (and dung as well) are valuable resources, full of complex proteins, carbohydrates, fats and sugars. And many creatures are ready to exploit the life opportunities offered by a corpse.

Dorothy flies up to her nest

April 20, 2022 • 1:01 pm

Well, Dorothy the mallard hen is well into the nesting phase, having unfortunately built this year’s nest on the windowsill right under the air conditioner in my office and right above the breezeway roof. This poses substantial logistical problems for getting her ducklings to the pond (see here).

Nesting hens sit pretty tight for several weeks, incubating their eggs, but they’ll fly down to the pond once every few days for a snack and a drink. (Dorothy seems to fly down every day, which may be suboptimal for incubation.)  She stays down for an hour or so, and I am usually around to feed her pellets and mealworms. A healthy hen makes for a happy and productive mother.

I took two short videos on my iPhone (the first I’ve put up on this site) showing Dorothy’s behavior when she’s had enough food, water, and preening and is ready to go back to the windowsill. She walks up the steps toward her nest (accompanied by her mate Pushkin, who’s been renamed from “Putin”), and then stands there for a while, bobbing her head all around as if checking the area. I’m not sure exactly why she does this, but she may indeed want to know that everything’s kosher before she gets back to the job of propagating her genes.

Here are two 30-second videos of Dorothy (and Pushkin) getting ready to fly. In the first she walks up the steps underneath her nest and stands there, looking all around with the faithful drake standing by. Enlarge the video (and the next) to see her bobbing her head about.

Here she finally takes off, and look how well she flies right into the gap under the A/C unit, where her nest is. Note too that Pushkin flies part way up with her, and then veers off. He goes back to the pond and settles down, occasionally quacking forlornly for Dorothy. He gets about an hour a day of quality time with her. Little does he know that she’s cooking up their offspring!

Adelie penguin defends Emperor penguin chicks

April 14, 2022 • 1:45 pm

I haven’t seen Emperor Penguins in the wild, as their breeding spots on the ice are far away from tourist access, and that’s fine.  But they do have a long march to the sea when they’re growing up. In this video clip from BBC Earth, a group of juvenile Emperors is having their March to the Sea when they’re attacked by a giant petrel.  He doesn’t succeed in hurting them, though, and for several reasons. First, they form a defensive circle facing outwards, and one of the chicks takes a protective stance with its wings out. (I find this amazing, but surely it’s hard-wired into the juvenile nervous system.)

And then an aggressive Adelie penguin shows up, further protecting the Emperors. Adelies are very small but they don’t take guff. What I don’t get in the video is that the fluffy chicks, who haven’t yet molted into adult plumage, are said to be ready to swim. They’re not. They won’t start swimming and fishing until they get their adult plumage.

Readers’ wildlife tale: Of figs and wasps

February 12, 2022 • 9:00 am

Today’s contribution is a biological tale of fig wasps, a fascinating species. (Do you know that every time you eat a fig, you ingest at least one wasp?) The photos aren’t from reader Athayde Tonhasca Júnior, but the story is, and it’s a good one. Click on the photos to enlarge them. Athayde’s tale is indented:

When ecologists talk about ‘keystone’ or ‘indicator species’, what they often mean is ‘my favourite species’, or ‘the species I work with’. But one group of organisms truly deserves the label of keystone species: figs. The genus Ficus comprises over 900 species spread throughout the tropical and subtropical regions as shrubs, lianas (woody vines), or trees. Strangler trees – which don’t strangle anything – are one of the best known types of fig plants.

Many fig species produce fruit asynchronously throughout the year, so many animals have a steady supply of abundant and nutritious food. This is especially important during the dry season, when most plants do not fruit. Figs are often preferred even when other fruits are available because they are rich in calcium, a mineral usually in short supply. So figs are essential for a range of birds and mammals such as pigeons, toucans, parrots, macaws, bats, peccaries and monkeys. Over 1,200 vertebrate species feed on figs.

Below: The strangler fig Ficus aurea © Forest Starr and Kim Starr, Wikipedia Creative Commons

Below: The diversity of fig fruit characteristics © Lomáscolo et al. 2010. PNAS 107(33):14668-72

Figs support the diversity and functioning of ecosystems around the world, but they can only do that thanks to some tiny wasps.

Below: Chalcid wasps are an enormous group of insects, estimated to contain over 500,000 species. Most of them are parasitoids of other insects, but a small group belonging to the family Agaonidae has one purpose in life: to get into a fig to reproduce. By engaging in fruit breaking and entering, these wasps, appropriately known as fig wasps, pollinate the fig plant.

The mission is made immensely complicated by figs’ morphology. Botanically speaking, a fig is not a fruit but a type of inflorescence known as a syconium (from the Ancient Greek sykon, meaning ‘fig’, which originated ‘sycophant’, or ‘someone who shows a fig’; a term of curious etymology). A syconium is a fleshy, hollow receptacle containing simplified flowers or florets, and each one of them will produce a fruit with seeds in it. A fig harbours dozens to thousands florets and fruits, depending of the species. The crunchy bits of the figs we eat are not seeds but fruits.

Florets need pollination, not an easy proposition when they are bunched up and locked inside a container. So the fig wasp’s first hurdle is to get inside the fig. A female wasp does it through a hole at the bottom of the fig (the ostiole), which loosens when the fig is ready for pollination.

Below: Longitudinal section of a syconium. The inner wall of the hollow chamber is covered with florets, and the ostiole at the bottom is the door for female wasps © Gubin Olexander, Wikipedia Creative Commons:

A receptive fig does not make life much easier for the female wasp. She has to chew her way through, pushing and squeezing, often having her wings and antennae snapped off in the process. She will find a floret, insert her long ovipositor into it and lay an egg. As she’s busy doing that, pollen grains attached to her body get rubbed off onto nearby florets, assuring their pollination. With the job done, the female wasp dies.

The ovules of florets that receive eggs will form galls in which the wasp larvae develop, while pollinated ovules turn into fruit. The adults chew their way out of the galls, males first. Sometimes they help females get out from their own florets and mate with them. Males will then chew a hole through the fig wall to let the females escape. Males stay behind: they couldn’t go anywhere, as they have no eyes and no wings. After an short life spent entirely inside a fig and marked by fleeting glorious moments such as fertilising females and setting them free, males die.

Below: two male Pleistodontes imperialis wasps on the left (wingless, smaller, black headed and amber-colored) and two females inside a Ficus rubiginosa syconium. The inseminated females have emerged from their individual flowers and are ready to escape © W.P. Armstrong, US Forest Service:

 

A female collects pollen grains from intact florets or picks them up by accident before braving the world outside. She will follow the trail of chemicals released by a host plant to find another fig receptive to pollination and start the cycle again. But she must be quick: she has a few hours to three days to live, depending on the species. And to complicate things, not any fig will do. Each species of fig tree is pollinated by one or a few host-specific fig wasps, which is an outstanding case of coevolution.

The great majority of female wasps don’t make it, but a few catch rides on wind currents above the canopy to find host plants over 10 km away, farther than most pollinators. This is a remarkable achievement for such small, fragile, and short-lived insects.

Perhaps nothing exemplifies better the wonders of fig pollination than the exploits of Ceratosolen arabicus in Namibia. This wasp pollinates the African fig tree (Ficus sycomorus) along the Ugab river in the North Namib desert. This is one of the most inhospitable and remote corners of the planet, famous for its Skeleton Coast, a place of shipwrecks and marooned sailors. African fig trees occur in isolated clumps along the riverbank, but that’s not a barrier for a female wasp: she covers average distances of near 90 km and a maximum of 160 km over the desert, at night, in search of a receptive fig. As she lives for less than 48 h, her quest must be flawless.

Below: Dry Ugab riverbed, Namibia © Theseus, Wikipedia Creative Commons:

How do figs and fig wasps relate to us, denizens of fig-less countries? This pollination system has a profound influence on global biodiversity and ecosystem functioning, so it affects us as well, even if indirectly. The story of figs and wasps also illustrates the capabilities, drive and hardiness of minute, easily overlooked insects that are so important for us and nature.

You can learn much more about figs and fig wasps at Figweb from Iziko Museums of South Africa.

The March of the Army Ants

February 9, 2022 • 1:45 pm

YouTube must have good algorithms when it comes to “suggesting” videos that you might want to watch: these appear on the right side of the page when you watch a video. And this four-minute clip, from BBC Earth, and narrated by David Attenborough, sucked me in instantly. Even though I was horrified, I couldn’t take my eyes off it

Well, it’s really not that bad, and it’s also biologically instructive. I have seen one of these columns in my life, and my instinct was to get the hell away from it!

Notice the strong selection imposed on potential prey to KEEP STILL if the army ants are there. So long as you don’t move, you’re safe. Those individuals who do move don’t leave their genes behind.

Here’s a related BBC video on “driver ants“, the African version of army ants: