Parasite makes ants into "berries" to entice birds

WASHINGTON (Reuters) - A parasitic worm can make its ant victims swell into what looks like a delicious, juicy berry to birds, which apparently eat the ants and help the worm spread and reproduce, U.S. researchers reported on Wednesday.

The nematode, a type of roundworm, changes not only the appearance of the ant but also its behaviour, with the ants holding out their bloated, glowing abdomens to entice the birds, the researchers report in The American Naturalist.

Robert Dudley of the University of California Berkeley and Steve Yanoviak of the University of Arkansas said the parasite and the way it works are new to science.

The black ants, found in the forests of Panama, are foul-tasting and not usually eaten by birds, they said.

Yanoviak acknowledged the team never saw birds eating one of the swollen ants but strongly suspected that they did.

"I definitely saw birds come in and seemingly stop and take a second look at those ants before flying off, probably because the ants were moving," he said in a statement.

"So I really suspect that these little bananaquits or tyrannids (flycatchers) are coming in and taking the ants, thinking they are fruit."

The researchers said that if the birds ate the ants, they could spread the worm's eggs in their droppings. These eggs would then be gathered by other ants who then feed and unwittingly infect their young.

"It's just crazy that something as dumb as a nematode can manipulate its host's exterior morphology and behaviour in ways sufficient to convince a clever bird to facilitate transmission of the nematode," Dudley said in the statement.