Spiders with the ability to glide have been studied for the first time. While most people may find this frightening, you need not be worried. These spiders live only in the tropical rainforest where foliage is thick and predators are plentiful. The rainforest can be a dangerous place and the ability to fly away from predators is a big advantage. Much of the wildlife living in the rainforest however doesn’t have this ability so several other strategies have evolved.
Some of the species of the genus Selenops, a group of spiders, have developed the ability to glide. To test their ability, the team, which was a joint effort of scientists from University of Louisville, University of California, Berkley and Smithsonian Tropical Research Institute, filmed 59 individual spiders, which were dropped from tree canopies. They also weighed the spiders to test what size was more favourable for gliding.
Of the 59 spiders tested, gliding was seen in 55 of them. Only 4 fell straight down without gliding. When gliding, the spiders flexed their legs towards they back which probably allowed them to catch more air. The researchers also found that lighter spiders generally had a greater ability to glide. They even observed some ability in the spiders to steer with their forelegs.
The team was fairly surprised to witness this gliding behavior in these spiders. Several other species of spiders have been tested for gliding ability and none had any. This behavior has been observed in some ants however, but the mechanism at which they do it is different. For example, ants glide backwards and steer with they’re hind legs, which are actually the leading legs while airborne,
It seems though that when Selenops spiders are threatened by a predator, they prefer not to jump off of the tree and glide. The researchers observed the spiders crawling over to the opposite side of the tree and hiding. As seen above, they are very well camouflaged so this strategy is probably equally as effective and saves them from a risky jump. In instances where they had to jump and glide, they tended to glide only a few meters and steer back onto the tree.
This discovery also has implications for the evolution of flight. It highlights the importance of flight in escaping predators in forested areas. It also provides us with a starting point for how flight may have started in some animals, though likely not birds. Wings are complex structures and would have taken several steps to evolve. The first step in flight may have been a similar gliding method seen in Selenops before wings were present, in an animal without wings or flaps between legs and arms (like in the flying squirrel). Over time, simple wings may have emerged due to genetic mutations, which would have given the animal an increased ability to fly and as wings improved, full on flight would have become possible. This may have been how flight evolved in flying squirrels.
There are still several questions the team has including how this spider finds a tree to land on or precisely how they steer.