New paper from the Hoy lab at Cornell! Paul Shamble, Gil Menda, and colleagues' paper came out in Current Biology this week. With behavioral and neurophysiological experiments they show that jumping spiders can detect airborne sound. You can watch Professor Hoy explain the findings in a video from Cell. This research is particularly cool because spiders have no tympanic membrane organ like our ears, or the ears of many insects. Although spiders have no ears they are very good at detecting substrate vibrations, as you can see if you gently touch a spider's web and the spider comes running. Additionally, many spiders can detect air disturbances through their body hairs, and use this to catch prey when they have no visual cues (that paper is here, but it's pretty tough going). This is like you being able to tell which way the wind is coming from by your hair blowing around, but much much more sensitive.
Spiders therefore, had previously been shown to be sensitive to substrate vibrations, and the movement of air particles at short range, but not to longer distance (3m) airborne sound. In this new paper the authors show that spiders freeze when low-frequency (80 Hz) sounds are played, even when they are placed on platforms that prevent them from detecting any substrate vibrations. Additionally, neural units in the spiders' brains were responsive to these frequencies. Given the sensitivity of spider hairs to air movement (and after all hair cells in our ears is how we hear), the authors suspected that spiders were hearing through the motion of their hairs. To test this they played sounds to a spider, found a neural unit that responded to that sound, and then moved single hair on the spider's leg and showed that the motion of the hair cell stimulated the same neural unit. It turns out that one of the main predators of jumping spiders are wasps, and wasps make a buzzing sound when they fly that is within the range of this spider's hearing. This auditory ability in spiders may therefore have evolved due to wasp predation. Jumping spiders are highly visual animals, which is not a surprise given their big eyes, and incredible courtship behaviors that include both visual and vibrational signals. I have always loved jumping spiders because when I one runs across my desk they always seem to stop and look me over, sizing me up. I admire their spunk. Now I will think about whether the sound of my typing was what rustled their leg hairs and made them look up.
I will leave you with the courtship display of a peacock jumping spider, because even though it is not particularly relevant to this story, it is just gorgeous.