Newswise — A number of tree-dwelling animals either glide through the forest air or parachute downward in what scientists call controlled descent, from so-called flying squirrels to lizards, frogs and snakes. Now, for the first time, a researcher has documented controlled descent in wingless insects—specifically, several species of arboreal ants.
Insect ecologist Stephen P. Yanoviak of the University of Texas Medical Branch at Galveston encountered the gliding ants in a rainforest near Iquitos, Peru, last year while he was climbing about 100 feet up in the forest canopy collecting mosquitoes for a project related to infectious disease. "I brushed the ants off the branch and watched in amazement as they glided back to the trunk in a J-shaped cascade," he said. "Since then, understanding gliding behavior in ants has occupied most of my free time."
Yanoviak discussed the novel discovery with colleagues Michael E. Kaspari, an ant ecologist at the University of Oklahoma at Norman, and Robert Dudley, a University of California at Berkeley biologist who specializes in flying and gliding animals.
Together they reported the findings mainly regarding worker ants of the species Cephalotes atratus in an article entitled "Directed aerial descent in canopy ants," to be published Feb. 10, 2005, in the journal Nature.
Said lead author Yanoviak: "It is the first documented example of directed aerial descent in a living wingless insect, and the first record of intentional backwards aerial gliding in any animal." It was also "completely unexpected," he said.
The authors report that despite dropping in steep glide trajectories at relatively high velocities of up to 12 feet per second, the ants "use directed aerial descent to return to their home tree trunk with greater than 80 percent success during a fall." A field experiment, they note, showed that the ants "use visual cues to locate tree trunks before they hit the forest floor."
The falling ants make spectacular 180-degree turns so that their flight path redirects them to their tree, with their abdomens and feet pointing towards the trunk. Often they bounce off, only to execute successive hairpin turns that effectively take them back to the tree.
Once there, they latch onto the tree trunk in ways the researchers do not yet understand, but which are perhaps analogous in the insect world to a fighter plane landing on an aircraft carrier—possibly with claws on their back legs serving as grappling hooks to secure them to the tree. Experiments in which Yanoviak dropped ants that had he painted white showed that, within 10 minutes or so, they had climbed as much as 80 feet safely back to the nest.
Why do these tree-dwelling ants glide? "To avoid getting lost," Yanoviak said, as well as to survive being brushed off branches by passing monkeys and to escape from predators such as lizards, birds and anteaters during their high-risk jobs of gathering resources from the lowland rainforest canopy and bringing them to the nest.
Directed aerial descent also spares the ants from the perils of falling onto treacherous and unfamiliar vegetation such as leaf litter in the rainforest understory or on the forest floor, or falling to certain death into portions of the flooded Amazon basin that teem with carnivorous fish. Yanoviak explained: "Leaf litter is particularly complex foreign terrain—and thus very hazardous—for a small animal that is adapted for following chemical trails along sunlit branches."
A foraging ant's death or disappearance "represents a net loss to the colony," Yanoviak observed. He said that natural selection should favor adaptations or innate abilities "that prevent worker attrition," and gliding in ants represents one such evolutionary example.
RSS