Tsetse (/ˈsiːtsi/, US /ˈtsiːtsi/, or UK /ˈtsɛtsi/), 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 African biological vectors of trypanosomes, which cause human sleeping sickness and animal trypanosomiasis, also known as nagana.