Ants Heal Themselves With an Aphid Diet

The gray-black slave ants know what to do when they are attacked by fungi: They temporarily change their diet.

Formica fusca

In matters of illness, ants and humans adhere to the same principles: when numerous individuals are crowded in a confined space, infection finds favorable conditions. It is not surprising, therefore, that social insects, such as ants, are considered adept at collective disease defense. Ants demonstrate precision in knowing whom to care for and from which conspecifics to maintain distance. Their efficiency extends beyond mutual medical care, as recent observations reveal their proficiency in self-medication.

Milking Aphids for Your Health

Ants have indeed developed strategies to manage fungal infections on their own. When the black slave ants (Formica fusca), prevalent in local forests, become infected with pathogens, they adjust their diet. They intensify their consumption of secretions from aphids. Researchers working with biologists from Graz have noticed that once the acute infection is under control, they return to their regular menu.

Ants are ubiquitous worldwide, facing the threat of various pathogens jeopardizing the health of their colonies. They have evolved an intriguing immune defense mechanism to cope with this menace. Jason Rissanen from the Institute of Biology at the University of Graz, in collaboration with colleagues from Finland, the Netherlands, and Germany, explored and published the study findings in the current issue of Biology Letters.

Disinfectant H2O2

Ants and aphids often coexist. The ants target the excretions of aphids, which not only contain carbohydrates but also valuable amino acids. Plants stressed by aphids produce highly chemically reactive oxygen-containing molecules (ROS), such as hydrogen peroxide. This compound, composed of hydrogen and oxygen (H2O2), is commonly used in households as a disinfectant and bleach. The free oxygen radicals are likely to enter the insects’ bodies through the honeydew that ants extract from aphids.

We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented

“We show that pathogen exposed colonies adjusted their diet to include more aphid supplemented foods during the acute phase of the infection,” summarized Rissanen in the recent study. For the study, ants affected by a fungal infection were offered food with three different concentrations of aphids. When infected, they consumed a higher proportion of crushed aphids during the acute phase of the infection. The hydrogen peroxide present in these tiny creatures, with its disinfectant properties, could play a role in combating the disease. “The mortality rate among the infected ants was significantly reduced due to the altered composition,” explained Rissanen.

End of the Diet

If the insects were healthy again after a few days, they spontaneously discontinued the aphid diet,” added Graz-based zoologist Dalial Freitak. The associate professor at the Institute of Biology and concurrently at the Tvärminne Zoological Station of the University of Helsinki in Finnish Hanko specializes in insect physiology and mechanisms of immune defense in insects.

The authors also addressed the significance of biodiversity as part of a complex system of nutrition and self-medication: The discovery of natural sources of medication and how animals use a diet to balance or directly combat immune responses helps to understand “how healthy and diverse ecosystems can provide animals with benefits against the ever-present threat of disease,” concluded the authors.

Featured Image: Formica fusca, the common black ant of Europe, Wikimedia.