Parasites Morph Ants to Look 'Berry' Tasty

Jan. 17, 2008 -- To perpetuate its life cycle, a newly identified parasite morphs its ant victims to such a degree that the infected ants resemble red, ripe juicy berries that birds are more inclined to pick, according to the University of California at Berkeley.

Eggs from the parasite then pass through the unwitting birds when they defecate. Ants consume the waste, become infected, and the whole cycle starts anew.

The transformation from black ant to red berry form represents the world's first known example of fruit mimicry caused by a parasite. In this case, the victimizer is a parasitic nematode, or roundworm.

The morphing process remains somewhat of a mystery, but the research team has a few theories as to how it happens.

"We think the worms either sequester pigment compounds from the exoskeleton or they make the exoskeleton thinner -- or maybe both," Stephen P. Yanoviak told Discovery News.

"The gaster (infected ant abdomen) does not actually take on a red pigment," added Yanoviak, an insect ecologist and assistant professor of biology at the University of Arkansas at Little Rock. "Instead it becomes translucent amber. With the yellowish (parasite) eggs inside and a touch of sunlight, it appears bright red."

Yanoviak and his team observed that infected ants hold their berry-ish bellies in an elevated position, which is an alarm posture in ants. Hauling around such a blob also makes the ants sluggish. Like ripe fruit, the gaster easily breaks off, so the combination of effects makes the "berry" easy for birds to pluck.

Normally, birds avoid consuming ants because they taste awful, they sting, have spines and possess a hard exoskeleton. The effort simply isn't worth the minimal nutrition ants could provide for birds in high canopy tropical forests ranging from Central America to the lowland Amazon, where the ant-to-berry phenomenon plays out on a daily basis.

The parasites even seem to make the ants more palatable to the birds, which think they are eating a berry from a Hyeronima tree, or one of the many other types of red berries found in tropical forests of the region.

"Infected ants seem to produce much less nasty pheromones," explained Yanoviak, who co-authored a paper on the new parasite with colleague George Poinar Jr., the world's authority on nematodes that parasitize insects. Their paper will be published in the February issue of Systematic Parasitology.