Myrmeconema, Cephalotes, the Amazon, and ants gone wild.

Myrmeconema is a nematode that parasitizes the ant Cephalotes in the Amazon jungle.  The nematode depends on birds to spread it around.  When an ant eats something that has nematode eggs on it, the ant's abdomen turns bright red and swells up and the poor ant has an irresistible compulsion to climb to a high branch and stick it's butt in the air.  A bird mistakes it for a berry and eats it, and then flies off and poops it out and the whole cycle starts again.