Woodlands Tsetsi Fly in Tanangire National Park. As we drove near the wetlands our truck filled with these critters. The wind pushed them toward the back of the vehicle but they were still a menace. They feed on vertebrates and their bite can inject trypanosomes, which cause human sleeping sickness. The flies are said to be attracted to dark red and blue (the Maasai colors). This one, smashed against the window left a tell-tale blood smudge; it's long proboscis is also visible.