Spider listens with its legs to seize flying bugs out of the air

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By Christa Lesté-Lasserre

The web spider with an ogre face

Jay Stafstrom

Some species of spider can apparently snatch prey from the air at night without seeing it, and now we know how. An analysis of such a spider shows that it picks up the sound of flying insects with its legs before it throws a web-like web over the unsuspecting animal.

The ogre-faced web spider (Deinopis spinosa), native to the southern United States, parts of the Caribbean and South America, is a Jekyll and Hyde-like creature, says Ronald Hoy of Cornell University in New York. During the day it disguises itself as a stick, at night it turns into a secret hunter.

The spider dangles upside down from its simple web, dives forward and throws a pre-spun web held between its four forelegs over the prey that goes by below, says Jay Stafstrom, also in Cornell.

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“We already know that they see the prey below them with their big eyes, because when we blinded them temporarily, they couldn’t catch anything below,” says Stafstrom.

Photo credit: Sam Whitehead

However, Stafstrom noted that the spiders could also perform backflips to catch insects flying overhead, although those insects were likely out of the spiders’ field of view. Stafstrom, Hoy, and their colleagues suspected that the spiders were using acoustic signals instead. In particular, they wondered if a little-known organ on spider legs, simply called “the metatarsal organ”, could detect sounds.

The researchers tested the animals’ reactions to recorded sounds that resemble flying insects. Then they tested isolated spider legs for nerve reactions to these noises alone. They found that the spiders were turning backwards to cast their webs when they heard recordings that resembled flying insect sounds, and their isolated legs exhibited nerve responses over a wide range of frequencies from 100 to 10,000 hertz.

“People always wonder if there are any aliens somewhere, but these spiders are just one example of the many aliens that already live among us,” says Hoy.

With bodies up to 25 millimeters in length, cast net spiders are relatively harmless to humans. “I was only bitten once,” says Stafstrom, who collects hundreds for his experiments before releasing most of them back into the wild. “It was in my hand for 10 minutes before it finally bit, and the bite only itched for a few minutes,” he says, adding that he hadn’t noticed any superpowers from the bite … until now.

Journal reference: Current Biology, DOI: 10.1016 / j.cub.2020.09.048

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