Humans are not the only organisms to take in lodgers some plants have ant ‘lodgers’ which acquire a home in return for protecting their host. The Crematogaster, or cocktail ants, for example, live in swollen galls of the whistling thorn, Acacia drepanolobium, and defend their host by attacking insect herbivores and biting browsers such as giraffe.

Scientists Renate Fischer, from the Institute of Botany at the University of Vienna, and research colleagues have shown that some ants living on plants also provide their host plant with nutrients. When Pheidole bicornis ants were fed with 15N-labelled glycine 15N was subsequently found in their host plants, Piper fimbriulatum and Piper obliquum, indicating that the plants received nitrogen from their ants. It is believed that the plant takes up nitrogen from the organic material such as stored food, debris and faeces which the ant surrounds itself with in its leafy home. The plants absorb the nitrogen from their leaf bases and young stems where the ants nest.

As well as providing nutrients for their host plants Pheidole bicornis ants protect their hosts from encroaching vines and herbivores. In turn ants receive a nesting space in a petiolar chamber at the base of a folded leaf and sweet nectar from single-celled food bodies made especially by the plant (Ecology vol. 9 pp126-134).

This biological story relating to animal-plant interactions was published in the BBC Wildlife Magazine