Catapult spiders (Theridiosoma gemmosum) do not wait passively for their prey to find its way into their web. Instead, they take action. These arachnids – also called ray spiders – pull back the center of their flat web, forming a cone with themselves at the end of the cone. They then hold the net in place by holding on to a tight anchor profile and then release the thread to let the web fly. The spider then catapults forward when an insect passes by, trapping the victim in a sticky coil.
VIDEO: A tethered mosquito with flapping wings is brought closer to the spider within the web’s capture cone, creating a contactless release. Video recorded at 500 fps, played back at 30 fps. The overall brightness and contrast have been adjusted. CREDIT: Reproduced by permission of The Company of Biologists. Han, S. I. and Blackledge, T. A. (2024). Directional web attacks performed by ray spiders in response to vibrations of airborne prey. J. Exp. Biol. 227, jeb249237 doi:10.1242/jeb.249237.
However, inside 2021biophysicists Saad Bahmla of the Georgia Institute of Technology and Todd Blackledge of the University of Akron and their colleagues discovered that they could trick the spiders into releasing these ballistic nets with a simple snap of their fingers.
Now Blackedge and University of Akron PhD student Sarah Han believe they’ve proven that slingshot spinning can listen for approaching insects and wait until the victims are within range before releasing the web and catapulting to their next snack. The findings are detailed in a study published on December 4 in the Journal of Experimental Biology.
[Related: Spider conversations decoded with the help of machine learning and contact microphones.]
For this new studyHan spent hours on the local riverbanks, peering into crevices and rocks looking for the distinctive cone-shaped webs with a spider on the tip.
“Slingshot spiders are very small, so they can be quite difficult to find,” Han said in a statement. “It takes some time to develop an eye for it.
Han brought the spiders back to the lab and set up some twigs for them to build a web on. She then went looking for some favorite spider snacks: mosquitoes and flies. Back in the lab, she attached individual insects – with their wings free so they could flap and make noise – to strips of black paper and wove them close to the cone-shaped spider webs as they filmed.
The spiders let their webs fly when the fluttering mosquitoes were near. However, further examination of the images revealed that the insects never touched the spider webs with their protruding forelimbs. Instead, the slingshot spiders were able to launch the webs before the mosquito even touched it.
Han then used a tuning fork set to the tone produced by the whining wings of a fly. When she placed it in front of the web, the arachnids still released their webs. The team thinks the spiders listened to the approaching insects released their webs as soon as the mosquitoes were close enoughbut before it ended up in there. The spiders may use sound-sensitive hairs on their legs to listen carefully to approaching insects.
VIDEO: A motionless tethered mosquito is stimulated to initiate wing beats. The onset of the mosquito’s wingbeats is quickly followed by the spider’s release of the web. Video recorded at 1000 fps, played back at 30 fps. The overall brightness and contrast have been adjusted. CREDIT: Reproduced by permission of The Company of Biologists. Han, S. I. and Blackledge, T. A. (2024). Directional web attacks performed by ray spiders in response to vibrations of airborne prey. J. Exp. Biol. 227, jeb249237 doi:10.1242/jeb.249237.
To find out how fast these webs fly once the spiders release them, Han charted the trajectory of each spider as they rode across the web as it tore forward. She calculated that the webs can reach speeds of almost one meter per second (3.2 feet per second) to intercept a mosquito within 38 milliseconds. The web shoots out much too quickly for an insect to escape.
Han also noticed that they were spiders 76 percent more likely to release their web cones when the mosquito is in front of the web. It only tried to release the web when the mosquito was behind it 29 percent of the time. The team thinks the spiders may compare the way they perceive sound transmitted through the web to their bodies to the sound vibrations transmitted through the air to their legs. This could tell them if an insect is in front of or behind their web and help avoid a costly misfire.
