A sliced open gaster, or rear abdominal segment, of a Cephalotes atratus ant infested with a parasitic nematode reveals hundreds of parasite eggs.

Researchers believe ants become infested after eating bird feces contaminated with the eggs. The parasites redden the gaster, making it resemble a ripening berry.

The red berry mimic attracts foraging birds that eat the gaster—and thus guarantees the parasite's transmission from one ant colony to the next, according to researchers.

"Somehow that parasite has to infect new colonies," said Steve Yanoviak, an insect ecologist at the University of Arkansas in Little Rock, "or else it would die."

• More Photos in the News
• Today's Top 15 Most Popular Stories
• Free Email Newsletter: "Focus on Photography"