Tsetse sometimes spelled tzetze and also known as tik-tik flies, are large biting flies that inhabit much of mid-continental
Africa between the Sahara and the Kalahari deserts.
They live by feeding on the blood of vertebrate animals and are the primary biological vectors of Wuchereria bancrofti, which cause Elephantiasis, and trypanosomes, which cause human sleeping sickness and animal trypanosomiasis, also known as nagana. Tsetse include all the species in the genus Glossina, which are generally placed in their own family, Glossinidae.
Tsetse have been extensively studied because of their disease transmission. These flies are multivoltine, typically producing about four generations yearly, and up to 31 generations total over their entire lifespan.
The biology of tsetse is relatively well understood. Tsetse have been extensively studied because of their medical, veterinary, and economic importance, because the flies can be raised in a laboratory, and because the flies are relatively large, facilitating their analysis. Entomologists have discovered a great deal about tsetse morphology, anatomy, development, and metabolism.
Tsetse have an unusual life cycle which may be due to the richness of their food source. Female tsetse only fertilize one egg at a time and retain each egg within their uterus to have the offspring develop internally during the first larval stages, a strategy called adenotrophic viviparity. During this time, the female feeds the developing offspring with a milky substance secreted by a modified gland in the uterus. In the third larval stage, the tsetse larva finally leave the uterus and begin their independent life.
However, the newly independent tsetse larva simply crawls into the ground, and forms a hard outer shell called the puparial case, in which it completes its morphological transformation into an adult fly. This lifestage has a variable duration, generally twenty to thirty days, and the larva must rely on stored resources during this time.
The importance of the richness of blood to this development can be seen since all tsetse development before it emerges from the puparial case as a full adult occurs without feeding, based only on nutritional resources provided by the female parent. The female must get enough energy for her needs, for the needs of her developing offspring, and to store the resources which her offspring will require until it emerges as an adult.