Directional web strikes are performed by ray spiders in response to airborne prey vibrations.

Most orb-weaving spiders use static webs that deform only after flying prey hit the webs. However, ray spiders (Theridiosoma gemmosum) pull orb webs into cones that are loaded with enough elastic energy to snap back like slingshots at accelerations of up to 504 m s-2 once released. We test the hypothesis that ray spiders sense vibrations from flying insects to release their webs and capture prey in mid-flight. We show that spiders release webs in response to live tethered mosquitoes that are not touching silk. Web release is most likely when mosquitoes are in front of the web and within the 'capture cone' where the capture spiral moves directly into the insects' flight. In summary, ray spiders use airborne stimuli to determine both the direction and distance of flying prey. Perception of airborne cues from flying insects may be an under-appreciated source of information for other web-building spider species about the approach, size and/or behaviors of insects prior to contact with webs.