Living high in the rainforest canopies of South America, selenopid spiders are at constant risk of falling. Because they don’t have wings, scientists had assumed they had little control over their fate. But a new study published online today in the Journal of the Royal Society Interface shows that they might have more than we realized: These arboreal spiders can control their falls, gliding from tree to tree to avoid the dangerous forest floor, just like flying squirrels. But the spiders don’t use webbing between their legs. Instead, they manage to stay aloft because of their wide, flat bodies. To find out just how agile the canopy-dwelling spiders are, the team went to Panama and Peru, where they dropped them from a height and filmed their descent (shown above). They found that 86% of selenopid spiders directed their falls toward nearby tree trunks, rather than simply plummeting to the ground. The researchers also filmed spiders’ movements in a wind tunnel, and found that they opt to fall head first, orienting their front legs to steer them to safety. Although small spiders commonly use a behavior called “ballooning,” in which they use a silk line to catch the wind and carry them to new locations, this is the first time that controlled gliding has been demonstrated in arachnids. Some ants and bristletails can also glide, and the authors say their trajectories are strikingly similar to the spiders, even though they use different techniques. Gliding ants fall backward and steer with their back legs, whereas bristletails fall forward and flex their abdomens for steering.
(Video credit: Science)