Selenopid spiders are at constant risk of falling because they live in the canopies of Central and South America's rainforests. Scientists thought that these arachnids have little control over what could happen to them when they fall down because they do not have wings.
Findings of a new study, which was published in the Journal of the Royal Society Interface, however, have shown that these spiders are more ingenious than what was previously thought.
The jungle spiders have the ability to control their falls. In fact, these arboreal arachnids free fall with style. After these spiders are dropped from the top of the trees, scientists have found that they can soar to a nearby tree trunk, a feat comparable to skydiving and provides evidence that spiders have the ability to glide.
Study researcher Stephen Yanoviak from the University of Louisville in Kentucky and colleagues took videos of these large spiders, also dubbed "flatties" because of their flat body, as they were dropped from a height of 24 meters at a research station located in the Amazon rainforest.
The spiders, from the genus Selenops, were observed to get into a posture comparable to that shown by skydivers then headed for a tree trunk. The researchers also found that most of the arachnids in the drop test directed their fall towards the nearest tree trunk traveling up to 5 meters horizontally as they steer their forelegs.
Small spiders often use a behavior known as ballooning through which they use a silk line to catch the wind, which would then carry them to a new location. The video of the selenopid spiders marks the first time that controlled gliding has been shown in spiders.
"These results are indeed surprising for a spider," said Marie Herberstein, editor of the book Spider Behavior. "Spiders generally rely on dragline silk ... as a safety line should they fall."
The findings also provide evidence that spiders can now be added to the list of animals that are capable of gliding such as some species of ants and silverfish.
The researchers think that the gliding behavior of the Selenopid spiders, which often run away when disturbed and jump off branches when they are pursued by predatory ants, has evolved because falling to the ground can be fatal for these spiders as they are likely to be eaten by predators.
"These spiders represent a remarkable evolutionary adventure in the animal conquest of the air," study researcher Stephen Yanoviak, from the University of Louisville in Kentucky, and colleagues said.
Photo: Katja Schulz | Flickr
