Can street vibrations keep spiders from detecting prey?

Noise pollution in densely populated urban centers can disrupt animal communication. Hungry nestlings may need to beg louder for their parents to hear over traffic. Some male birds change their tune to attract females in the crowd. While vocalizations get most of the attention, excessive noise traveling through solid materials could mask the cues used by species in touch with vibrations.

Orb-weaving spiders, for example, often detect prey caught in their web from its movements. Webs built near cacophonous activity, such as a construction site, may vibrate constantly and drown out any buzz from real prey, perhaps allowing time for it to escape. In addition to a web’s street address, a supporting substrate made of manufactured materials may dampen or amplify vibrations transferred from ambient noise. Although only one part of the urban microfauna community, understanding spider responses to noise may give insights into planning a more harmonious city soundscape.

Two biologists at UC Berkeley surveyed webs around campus to find out what substrates, natural or artificial, spiders were using. To quantify differences in the amplitude of vibrations from ambient noise between substrates, they brought a portable laser vibrometer into the field. Three levels of noise vibration were replicated in a controlled lab experiment with captive European garden spiders, Araneus diadimatus. Prey detection rates were determined for each noise level by simulating entrapped prey with another vibrator in contact with the web.

Almost half of the free-roaming spiders attached their web to at least one artificial surface, mainly metal, concrete, or glass. Surprisingly, all substrate types vibrated more from wind than traffic noise. The artificial substrates were the stillest, or quietest at higher ambient noise levels. Even more surprising, spiders in the lab detected “prey” the easiest over the background vibration level simulating wind-generated noise. Increased movement of the web from wind may have put spiders on high alert from the constant stimulation, at least in the short-term without time to habituate.

Artificial surfaces turned out to matter more than artificial noise. In windier spider neighborhoods, spinning a web on quieter concrete may actually hinder prey detection before it escapes. Natural substrates like flowers, shrubs, and trees may also be higher quality if that’s where prey are more abundant.  And where there could be less risk of being swept off all eight feet by a fastidious broom-wielding arachnophobe. Miles Becker | 24 February 2014

Source: Wu, C.H. and Elias, D.O. 2014. Vibratory noise in anthropogenic habitats and its effect on prey detection in a web-building spider. Animal Behaviour   doi: 10.1016/j.anbehav.2014.01.006

Photo © Ray Habens