Ant Plants

Some plants pay for an army of ant bodyguards by providing their protectors with shelter and food.

If you think the housing market is tough in San Francisco, try being an ant in Madagascar. With thousands of insect species competing for space in the same twig, log or leaf litter, finding a safe place to nest is a challenge - which is why at least two ant species have learned to live inside the hollow stems of Madagascar's melastome plants. On a recent expedition to this island off the coast of Africa, Academy entomologist Brian Fisher discovered these new ant species and their accommodating hosts, which are the first "ant plants" known from Madagascar.

Ant plants are relatively common in the tropics, where plants are swarmed by predators. By providing special living quarters for ants inside their stems or leaves, ant plants acquire a highly effective defense system. Because of their natural inclination to protect their home, ants that live in the plants will fight off other insects, larger herbivores, and even encroaching vines. Sometimes this mutually beneficial relationship extends to food as well. Some ant plants produce protein-rich food nodules for their inhabitants and absorb nutrients from the ants' waste in exchange.

Before the recent expedition, Fisher was puzzled by the apparent lack of ant plants in Madagascar, since they are abundant in Africa, Asia and South America. Now he has a new puzzle to solve - the Madagascar ant plants are much more closely related to South American ant plants than they are to their African neighbors.

Cross section of the hollow melastome stem that provides a living area, called a domatia, for these specialized ants. Photo: Dong Lin

 

Ants of the genus Leptothorax leaving the swollen, hollow stem that serves as their living quarters. The stem includes a weakened wall that the ants can chew through to access the interior of the hollow stem. Photo: Dong Lin
Brian Fisher with porters in the rain forest near the summit of Anjanaharibe. Photo: Dong Lin
Newly discovered melastome sp. ant plant along a stream near the summit of Akirindro mountain. Inset: Flower of plant in the family Melastomataceae.c
Photo: Dong Lin