tsètsè

Tsetse comes from Tswana tsètsè (pronounced roughly 'tset-seh'), which means fly in the Sotho-Tswana group of Bantu languages spoken in what is now Botswana, South Africa, and Zimbabwe. The word entered English around 1849, appearing in the journals of explorers and missionaries traveling through southern Africa, and was adopted as the English name for the genus Glossina — the large, blood-sucking flies that transmit the parasites causing African sleeping sickness in humans and nagana in livestock. The name 'tsetse fly' therefore means 'fly fly,' a redundancy that linguists call a tautological compound or pleonasm: the same referent named twice, once in the source language and once in the target language. This pattern is common in borrowings where the meaning of the loanword is not understood by the borrowing community.

The tsetse fly belongs to the genus Glossina (from Greek glossa, tongue — for the fly's piercing mouthpart) and comprises around 23 species distributed across sub-Saharan Africa, concentrated in the tsetse belt that runs from the Sahel south to the Kalahari. Its ecological significance is enormous: tsetse flies transmit trypanosomes, single-celled parasites that cause trypanosomiasis — sleeping sickness in humans, nagana in cattle and horses. The disease has shaped African history in ways that are still not fully appreciated. Large areas of potentially productive agricultural land have been uninhabitable for cattle-raising cultures because of tsetse presence. The expansion and contraction of tsetse ranges, driven by climate and land cover change, has repeatedly altered which areas of Africa were viable for settled pastoralism.

David Livingstone's encounters with the tsetse fly, documented in his Missionary Travels and Researches in South Africa (1857), helped introduce both the word and the insect's significance to a British reading public. Livingstone described watching his pack animals die of nagana — the livestock disease spread by tsetse — and recognized, correctly, that the fly was the vector. This was before germ theory, before the discovery of trypanosomes, before any understanding of disease transmission: Livingstone's observation that a fly bite caused disease in animals was a piece of acute natural history that preceded the scientific framework that would eventually explain it. He borrowed the Tswana name as the only available one and used it throughout his accounts.

The tsetse fly has also had a paradoxical role as an inadvertent conservationist. By making large areas of Africa unsuitable for cattle ranching, tsetse presence preserved some of the continent's greatest wildlife habitats. The Selous Game Reserve in Tanzania, the Luangwa Valley in Zambia, and significant portions of the Okavango Delta in Botswana owe their status as intact wildlife ecosystems in part to the fact that the tsetse fly made sustained cattle-raising impossible there. Conservation biologists have called this the 'tsetse factor': the parasite's host specificity and the cattle mortality it causes served, unintentionally, as a barrier to the kind of land conversion that has destroyed wildlife habitats elsewhere. The fly that transmits disease also, incidentally, protected some of Africa's most extraordinary landscapes.