Magazine article Science News

Ants Evolved Swimming Several Times: Multiple Species Can Rescue Themselves after Falling from Trees

Magazine article Science News

Ants Evolved Swimming Several Times: Multiple Species Can Rescue Themselves after Falling from Trees

Article excerpt

In the tropics, some ants living high in trees can swim well if an accident--or a scientist--drops them into water.

Some form of swimming has evolved independently several times in ants, says Steve Yanoviak of the University of Louisville in Kentucky. In swim tests, the champs powered across the water at more than three body lengths per second, he and Dana Frederick of the University of Arkansas at Little Rock report in the June 15 Journal of Experimental Biology.

Tropical ants have plenty of water to worry about, especially where rivers flood acres of Amazonian forest so deeply that fish swim among the trees for months each year. Ants that plummet from their treetop homes may drown, get gulped by aquatic predators or, just as fatally, be swept downstream far enough that they can't find their colony again. "If you're a wingless animal living high in a canopy, then you have to deal with what happens when you fall," Yanoviak says.

Some ants can glide through the air to a tree trunk, Yanoviak discovered in earlier research that involved dropping ants out of trees (SN: 2/12/05, p. 101). Still musing about falls, Yanoviak took ants to a wooden footbridge over swampy pools in Peru. "I dropped a couple of ants and totally expected them to just struggle at the water surface and become fish food." Many did. But ants in a few species "basically stood up and ran across the water surface and climbed out--no problem."

The ants that appeared to run on water did have their feet sink a little, and some ants' legs sank more deeply but could still row along. To see if ants might have natural tendencies to rush toward tree trunks while swimming, the researchers got a vinyl Winnie the Pooh kiddie pool and set a white or black pole in the water against the perimeter. …

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