Hoisting

February 11, 2011

Tags: Olios, Pellenes, Sparassidae, Salticidae

The "conchicolous habit"--hermit crabs have it, some bees and wasps have it, but a few spider species lift shell dwelling to new heights: they use silk to hoist their prefab homes into the air. A BBC crew working in Madagascar has finally caught the efforts of one of these species, Olios coenobitus, on film.



O. coenobitus is in the family Sparassidae, the huntsman spiders. At least one other species, Pellenes nigrociliatus, a jumping spider (family Salticidae), has also been found living in suspended snail shells, in Poland. Neither of these spiders can produce the stretchy silk used in the catching spirals of orb weavers and their descendants. In fact, few spiders in either of these families make any kind of web. Their hoisting ropes consist of major ampullate dragline silk, the super-strong silk araneomorph spiders use to rappel. In the lab, these spiders have been observed to lift shells more than 20 times their own body weight.

It might seem inconceivable that the same strange behavior would evolve in two species of spider that aren't terribly closely related. But it looks strange only to us humans. An empty shell isn't so different from the burrows spiders dig themselves or the crevices in bark they often occupy. And spiders frequently use silk to suspend killed prey and egg sacs. They pull on silk threads all the time to bring them under tension. We'll probably never know exactly how this feat evolved, but many spiders already had the tools and behaviors needed to accomplish it. Looked at that way, it's surprising this behavior hasn't evolved more often. But then again, even these spiders' closest relatives get along fine without it. In evolution, "good enough" is good enough.

Read how the film was made here.

Jump, Thump

July 31, 2010

Tags: Salticidae, Elias

All spiders make silk. For many spiders, silk is about building someplace to stay still. But for jumping spiders, it's about having the freedom to move around. Fast.

Jumping spiders make up the family Salticidae. This is the biggest spider family, numbering about 5,000 species. No matter where you live, you've probably come across a jumping spider one time or another in your home. They're usually compact, and because they're diurnal, you may find them traveling across the kitchen table or a windowsill or wall in broad daylight. (Also, it has to be said: magnified, they're quite quaint. There's something about those big, forward-facing eyes and fuzzy chelicerae that evoke King George V on a bad hair day.) Don't torment it, but it's really fun to nudge a jumping spider from behind and watch it spring away. Even more fun is to watch one jump perpendicularly away from a wall and then seemingly defy gravity as it lands back on the wall a few inches down.

You have to look closely to see the secret behind this daredeviltry. Salticids belong to the spider infraorder Araneomorphae, all of whose members produce major ampullate, or dragline silk. All araneomorphs can dangle on major ampullate silk threads. In fact, it's likely major ampullate silk evolved because stronger silk allowed more spiders to drop out of the way of danger. Salticids just took this innovation and leapt with it. This super-strong silk lets them recover from any jumps they might miss: it reels out from their spinnerets as a safety line as they travel through the air.

We're only beginning to understand how much we don't see and don't hear and otherwise don't sense what's going on in the miniature world of the jumping spiders. I was reminded again of how much sheer imagination and creativity are involved in experimentation--qualities often masked by the dry prose of scientific papers--when I recently came across this amazing PBS film about Damian Elias's research on jumping spider courtship. Enjoy:






Tags

"...a compelling introduction to evolution in action through the lens of spiders and their silks."

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