From Scientific American:
For the past few millennia, ants of the Attini tribe have tended gardens of fungus that they eat. Over the past few decades scientists have studied these agricultural insects, trying to understand how their gardens grew in the first place. Now a group of scientists have discovered that the ants carry a potent antibiotic bacteria in special pockets on their bodies that help control a parasite that can ruin their fungus harvest.
Entomologist Cameron Currie of the University of Wisconsin and his colleagues discovered the antibiotic bacteria in crescent-shaped pits on the exoskeletons of two species of Panamanian ants, Cyphomyrex longiscapus and C. muelleri, after scanning them with an electron microscope. The bacteria–of the Pseudonocarida genus–bloom on the individual face plates and other exterior parts of the ant, allowing it to rub the antiparasitic agent on its fungi crop. The ant also nurtures the microbe by secreting nutrients from special exocrine glands connected to the shallow pits.
More here.