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).
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.
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.
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.