The effect of fire on swollen-thorn acacias and their tenant obligate acacia-ants in the Central American dry lowlands is discussed. Fires may either consume the entire acacia shoot and ant colony, scorch and kill the acacia but not the ants, or kill neither acacia nor ant colony. Which alternative occurs depends on the structure of the immediately surrounding vegetation which in turn depends on how much of it has been killed by the ant colony and how fast the acacia has grown. The survival of the acacia population in frequently burned areas is almost entirely dependent upon some ant colonies surviving the fire to occupy the new sucker shoots from acacia stumps. The effect of these fires on the evolution of the interaction between the ant and the acacia is discussed. ©Ecological Society of America. Abstract reproduced by permission.