A new species of parasite that makes ants change colour to resemble berries has been discovered in Central America. Researchers behind the finding think this is part of a strategy to fool birds into eating the ants, thus distributing the parasite.
(As an aside, this is tame compared to Leucochloridium paradoxum which invades a snail and makes it glow to attract birds.)
Back in 2005 Robert Dudley of UC Berkeley noticed that some members of a colony of black ants had bright red abdomens. He took them back to the lab and showed them to Michael Kaspari and Stephen Yanoviak, who thought they were a different species.
“Robert didn’t think so, and we made a bet over beers,” says Kaspari (press release). “Then Steve opened one up under the scope and – wow! I lost the bet.”
When opened up the red ants were full of hundreds of nematode eggs. “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,” says Dudley.
The researchers reconstructed the life cycle of the nematode and believe that infected ants are eaten by birds who then excrete the eggs to the ground with seeds and insect parts. Infected bird droppings are then gathered by ants and fed to their young, who become hosts and repeat the cycle. As well as becoming red, infected ants become sluggish and hold their abdomens high in an alarm gesture. This abdomen also becomes easy to break off. Taken together this all seems pretty convincing.
One problem: they haven’t spotted birds actually eating any of the red ants. “Nevertheless, 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. So I really suspect that these little bananaquits or tyrannids (flycatchers) are coming in and taking the ants, thinking they are fruit,” says Yanoviak.
A report on the new nematode appears in the journal Systematic Parasitology (link). According to the press release a report on the finding will also appear in The American Naturalist in Spring.
Video of the ants
Parasite makes ants into “berries” to entice birds – Reuters
Ants forced to con birds in worm’s 3-way reproductive strategy – SF Chronicle
Image top: Comparison of normal worker ants (top) and ants infected with a nematode / Steve Yanoviak/University of Arkansas
Image bottom: Infected ant’s abdomen sliced open to reveal nematode eggs. Closeup shows the worm coiled inside egg / Steve Yanoviak/University of Arkansas