( Nature. After Yanoviak's initial obs...)Falling ants glide back to trunk to avoid dangers of forest floor

After Yanoviak's initial observation, he conducted further drop studies and established that about 85 percent of the ants ?a widespread tropical canopy species called Cephalotes atratus ?are able to land on the tree trunk and climb back up, as compared to a mere 5 percent that would be expected to land on the trunk if the ants were parachuting randomly to the ground.

"I noticed this five years before in Panama, but it was at that moment in Peru 18 months ago that I realized why they do it: They're trying to get back to the tree, they're trying to not get lost in the understory of the forest," he said. Once they hit the forest floor, he added, they're unlikely to find a chemical trail back to the nest, and most likely will be eaten by predators.

Yanoviak said that perhaps more important from the perspective of survival, the forests are flooded as much as half the year, so an ant falling into the water will most likely end up as fish food.

"That's what I think is the major evolutionary driving mechanism behind the behavior," he said. "In Amazon forests, you really don't want to fall out of your tree and in the water, because then you're definitely dead."

After capturing some quick video snippets with his digital still camera, Yanoviak contacted UC Berkeley's Dudley to arrange a more scientific study of the ants' gliding behavior. They met up with Kaspari last summer in Panama for a week to videotape the same species of ant in freefall, with a white sheet standing in for the tree trunk.

Yanoviak's earlier observations combined with the videotaped tests in Panama established that the ants basically reorient their bodies so their hind legs and abdomen point toward the tree, and use their head-up fall through the air to take them feet-first toward the trunk. How they land is still a mystery, but evidently claws on their back legs act like grappling hooks to snag the trunk and hang on.

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Source:University of California - Berkeley