Graz Study: Caffeine Slows Fungal Infection in Ants and Prolongs Their Activity

Laboratory Result

"The ants remained active longer and mortality was delayed," Nyckees is quoted as saying in a press release. The research team speaks of an antifungal effect of caffeine. As such, the substance not only slowed the course of the disease but also indirectly strengthened the animals' chances of survival.

The observation fits a well-known pattern: other insects also adjust their diet when they are sick. Some species then eat more protein-rich food to boost their immune system. Bees, for their part, collectively raise the temperature inside the hive to kill bacteria. The Graz study now shows that targeted self-medication with plant substances may also belong to this repertoire.

Caffeine in Nature

Caffeine occurs in nature in around 80 plant species worldwide. Well-known sources include coffee beans, tea leaves, and cacao. "In the Mediterranean region, for example in citrus plants," adds Dalial Freitak, head of the Insect Health and Biology research group at the University of Graz. That means ants in many habitats would have access to caffeinated plants.

For the study, the caffeine was "served" to the insects in the laboratory by the research team from Graz and Oulu in Finland. The animals were able to choose between various food options. Infected ants preferentially opted for the caffeinated variant, while healthy conspecifics spurned it.

The zoologist Freitak, who teaches in Graz, considers ants an ideal model for researching the mechanisms of immune defense. Ants are found almost everywhere on Earth, even though their colonies are threatened by a large number of pathogens. The current results provide another piece of the puzzle in understanding this defense.

Significance for Research

The study was recently published in the journal Animal Behaviour under the title "Can caffeine improve the survival of the ant under pathogenic infection by the fungus?" The authors are D. Nyckees, Ch. Hahn, H. Helanterä, and D. Freitak. The paper is accessible via ScienceDirect.

The researchers see in the results an indication that the capacity for self-medication in social insects may be more widespread than previously assumed. Should the effect be confirmed in further experiments, this could also change the perspective on the evolutionary benefit of caffeine-producing plants.

Overall, the Graz investigation offers an unusual bridge between an everyday stimulant and a natural phenomenon: a substance that keeps humans awake could, in tiny doses, also help ants resist a deadly infection for longer.

The dose of 100 milligrams per kilogram roughly corresponds to the concentration found naturally in plants – not the amount contained in a cup of coffee. For the ants, therefore, it is a matter of a medicine from the environment, not a stimulant.