In the dark of night, ogre-faced spiders with dominating big eyes dangle from a silk frame to cast a web and capture their ground prey. But these spiders also can capture insects flying behind them with precision, and Cornell University scientists have now confirmed how.
In a new study, researchers confirmed these spiders use metatarsal sensitivity — sensors at the tip of the leg — to detect sound cues of various frequencies from up to 6 feet away. These cues trigger a split-second, ninja-like backflip to strike unsuspecting airborne insects, bag them in a web net, and then dine.
“These spiders have finely tuned sensory systems and a fascinating hunting strategy,” said lead author Jay Stafstrom, a postdoctoral researcher in the laboratory of Ronald Hoy, professor of neurobiology and behavior at Cornell. “These spiders have massive eyes so they can see at night and catch things off the ground, but they can ‘hear' quite well, detecting sounds through their metatarsal organ, as these spiders excel at catching things from the air.”
Net-casting, ogre-faced spiders (Deinopis spinosa), are nocturnal creatures found mostly in the southeastern United States. While people are familiar with spiders that create orb webs, this species makes personal, fuzzy webs — like small nets — and uses the strong, sticky silk like a baseball glove, according to Hoy.
Spiders don't have ears, but they can sense a wide range of sounds thanks to the metatarsal organ located near the tip of their legs.
Stafstrom collected these spiders and brought them to Gil Menda, a postdoctoral researcher in Hoy's lab, who recorded neural activity from both their brains and their legs. He played pure tone frequencies to the spiders and noted the spider's neurons became excited for difference tones.
Stafstrom examined frequencies that ranged from 150 Hz (the flute-like sound of blowing over a glass soda bottle) to 750 Hz (the high-pitched drone of a local television nighttime sign-off) to 10 Khz, a piercing, high-pitched sound.
“While the spiders were sensitive to low-frequency tones, as expected, we didn't really expect to see net-casting spiders sensitive to a wide range of frequencies — all the way to 10 kilohertz,” he said.