This just in: Scientists have discovered that several species of spider have power-amplified jaws that snap shut like a venomous bear trap.
“This was totally unexpected,” says Hannah Wood, curator of arachnology at the Smithsonian National Museum of Natural History and lead author of a study published today in Current Biology. “It’s never been observed before.”
The good news for all you arachnophobes? The spiders are ever so itsy bitsy.
The smallest trap-jaw spiders, all in the Mecysmaucheniid family, measure less than two millimetres – that's roughly equivalent to half a grain of rice. In fact, these spiders are so tiny, the only way Wood could get them to chomp on command was by poking them with one of her eyelashes attached to a needle!
So far, the spiders are known to exist only in New Zealand and South America, where they prowl about the leaf litter. From her own observations, Wood suspects they are ambush predators, waiting for a victim to wander into their open maws. The attack itself is triggered when prey brushes up against tiny trigger hairs on the spiders’ chelicerae, or jaws.
As to what exactly the puny predators are catching, Wood isn’t quite sure. Gauging by mealtimes in the lab, the larger species appeared to be unfussy eaters, but their smaller cousins – who are also the ones with the fastest, most powerful bites – seemed to have an appetite only for springtails, tiny arthropods also called Collembola.
Wood admits we have almost no observations of what the spiders may be eating in the wild, but the fact that they have a taste for springtails is telling. Like their name suggests, springtails have a tail-like appendage called a furcula that can strike the ground with so much force, the arthropods use it to pole-vault out of danger. For spiders who target such nimble prey, an equally swift way to capture it would come in handy. At this stage, though, it’s anyone’s guess.
“If you’re working on a lion and you want to know what it’s eating, you can find them and observe them,” says Wood, “But these tiny things, they’re very hard to observe in the wild.”
If the spiders were just slightly larger, say the size of ants, it might make a world of difference – you might be able hold them in place and take high-resolution videos of their strikes. But nobody puts the Mecysmaucheniids in a corner, apparently. When Wood tried tethering them in place, the spiders just sat there pouting and refusing to perform.
In the future, Wood hopes to sequence the genomes found in the spiders’ guts as another way to get a glimpse into what they’re eating. Similarly, her co-author Dilworth Parkinson at the Lawrence Berkeley National Laboratory in California has been helping her image the spiders’ heads with a particle accelerator.
Essentially performing an MRI on a spider, the duo has started creating models that let them digitally dissect the arachnids. And while they’ve discovered all sorts of interesting morphological adaptations – such as huge venom glands and meaty mandible tendons! – the inner workings of the bite mechanism remain a mystery.
We do at least know that the force produced by the smallest spiders’ bites would be impossible to achieve by muscle power alone. That means there must be some sort of mechanical anatomy at play, a way for the mandibles to store energy and then release it rapidly – like a spring or compound bow.
“There’s still so much we don’t know about spiders,” says Wood. “There are over 45,000 species and there are still many, many species to describe.”
Perhaps Wood’s research will inspire other scientists to start giving trap-jaw spiders a closer look. As it stands, she remains the only person on earth investigating these species ... one eyelash poke at a time.
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Video and header image: H. Wood
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