Tsetse fly: The bloodsucking insect with a saw for a mouth

Tsetse flies transmit some of Africa’s most persistent parasitic diseases. They have affected human health, livestock production and rural development for generations, across a region spanning millions of square kilometres in 37 sub-Saharan countries.

Human African trypanosomiasis, or sleeping sickness, is caused by two species of single-celled parasites. Others infect wild and domestic animals, causing animal trypanosomosis, often called nagana in cattle.

Sustained surveillance, diagnosis and treatment have driven sleeping sickness to historically low levels, a remarkable public-health success. But animal trypanosomiasis remains a major problem, causing anaemia, weight loss, reduced productivity and fertility and death. For rural communities that depend on cattle for food, income and for use in tilling fields, the consequences extend far beyond the loss of individual animals. Across affected regions, the economic costs run into billions of US dollars.

Tsetse flies move between hosts. They take blood from humans and a wide range of wild and domestic animals, including elephants, buffalos, rhinos, hippos, turtles and monitor lizards. By moving between hosts, tsetse flies can connect wildlife, livestock and humans in complex transmission networks.

We are molecular cell biologists and parasitologists researching vectors, and we have extensive laboratory and field experience studying African trypanosomes and tsetse flies. Our work focuses on the interactions between parasites and their insect vectors, including the adaptations that allow tsetse flies to thrive across diverse ecosystems.

For a recent study, we assembled an international team spanning parasite biology and cell biology in Würzburg, vector research at the International Centre of Insect Physiology and Ecology in Nairobi and insect biomechanics in Kiel. We wanted to understand how the insects can penetrate such diverse skin types.

We detailed the anatomy and mechanical properties of the feeding apparatus and measured the forces a fly exerts while probing. We found its ability to pierce skin wasn’t due to one special “tool”. Instead, rows of tiny teeth, strong backward strokes of the mouthparts and flexible behaviour work together. The flies used the same pressure on very different natural skins and, when faced with reptile skin, selected softer gaps between scales.

This versatility helps explain how tsetse flies feed across such a broad host range – and therefore why they are so effective at carrying parasites among wildlife, livestock and humans.