Here's a story about a parasitic nematode that turns black ants into ripe red berries. What's this about?
The parasite needs to get its eggs from an infected ant to healthy ants. Apparently it hasn't been successful the old-fashioned way, just broadcasting its eggs about the environment. Instead, these little worms have figured out a far more effective egg delivery vehicle: birds.
Ants of the genus Cephalotes often feed from bird droppings (for instance, see here). If a parasitic egg can get itself into a bird's digestive system, it'll wind up in a juicy fecal pellet where it may be inadvertently picked up by hungry ants.
The manner in which the nematode reaches a bird is particularly clever: parasites of reproductive age make the infected ant look like bird food. The rounded end of the ants' abdomen (the gaster) turns from black to red, and infected ants raise their gasters high in the air where they appear like ripe berries. Bird eats ant, bird poops out parasite eggs, ants eat egg-laden poop, ants begin to resemble bird food, and the cycle continues.
photos by Steve Yanoviak