Spiders living in the treetops of South American rainforests were found to glide to safety when dropped from their canopies. Reported in the Journal of the Royal Society Interface, this is the first evidence of spiders being able to control their aerial descent.
The glider spiders
The tropical rainforest canopy is home to many arthropods, a class of invertebrate animals that have segmented bodies and jointed feet. The winged members of this class manage to easily get away from predators by flying. On the other hand, wingless arthropods could be in a lot of danger should they fall close to the ground. The understory area is new territory for these creatures and makes them vulnerable to attack by ground-dwelling animals. Many of these wingless creatures, like ants, have therefore adapted to orienting their falls towards tree trunks by gliding at steep angles. This behavior hasn’t been seen in insects related to spiders, and only now has it been discovered in the spiders that reside in the lowland rainforests. These spiders belong to the genus Selenops; they are camouflaged, nocturnal hunters that hide in tree crevices during the day. They are commonly known as “flatties” because they look like they have been pressed flat.
Scientists document the spiders gliding
The flying study was conducted in the Barro Colorado Island in Panama and the Amazon Conservatory for Tropical Studies in Peru; the Selenops spp. spiders were collected from trees and stored in the lab overnight for measuring their weight and their body geometry. After that they were subjected to drop tests from either a tree trunk or a raised platform. Of the 59 spiders tested, 55 (93%) flews straight to the tree trunk. Scientists called this directed aerial descent because the spiders were able to orient themselves with their belly down, hind legs angled backwards, and head directed towards the tree trunk (see video here).
What could this mean?
Gliding from treetops to find a safe landing is a sophisticated maneuver that spiders have developed for self-preservation. It would be interesting to see if gliding can been seen in other related creatures and what cues, if any they could be using to elicit this sky diving-like behavior.
