National Geographic : 2000 May
KILL OR BE KILLED Dwelling within hollow branches of the tree Cordia nodosa, the orange-colored workers of an Allomerus colony dismember the corpses of their enemies (bottom right). Allomerus is a parasite: It sterilizes its host by dismantling the tree's flowers (below). With its energy diverted from reproduction, the tree grows larger, thereby providing more living space for the colony. Other ants are mutualists: They encourage reproduction of their habitat by protecting the host's flowers. Studying Cordia and other ant plants in Peru, biologist Doug Yu plucks vicious Pseu domyrmex ants from a Triplaris tree, its base cleared of vegetation by the ants (bottom left). In West Africa Leonardoxa africana trees harbor either Petalomyrmex phylax, a helpful ant that kills leaf-eating insects, or Cataulacus mckeyi, a parasite. The "good" ants keep out competitors by shaping their nest entrances as narrow slits, which a round-bodied Catau lacus queen cannot enter (right).