60-Second Science

Parasitized Ants Get Berry Sick

A nematode parasite causes ants to look like berries that birds like, putting ants on the diet and helping to spread the parasite. Cynthia Graber reports.

When is an ant like a piece of fruit? When it’s infected by a parasite. Researchers affiliated with the Smithsonian Tropical Research Institute discovered this bizarre occurrence in Central America as they were studying the gliding ability of a certain species of ant. They found some colony members with bright red swollen abdomens. The scientists took specimens back to the lab and discovered they were full of hundreds of nematode eggs. The bright red bellies look suspiciously like the brilliant red and pink berries that proliferate in the rainforest.

Researchers think that the nematode makes the ant look like fruit to get birds to eat the ants. Birds usually keep the ants off their menu because of armor and a bad chemical taste. The birds then spread parasite eggs in their droppings. Ants forage through bird droppings for seeds. They feed the infected droppings to ant larvae, beginning the infection process all over again. The red-bellied ant is the first known case of a parasite causing fruit mimicry. One of the researchers was surprised that something “dumb as a nematode” can manipulate its host in such a sophisticated way.  But evolution works no matter how dumb organisms are.

--Cynthia Graber

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