Tsetse next develops a hard external case, the puparium, and become pupae – small, hard-shelled oblongs with two distinctively small, dark lobes at the tail (breathing) end.
Tsetse pupae are under 1 centimetre (1⁄2 in) long. Within the puparial shell, tsetse complete the last two larval instars and the pupal stage.
At the end of the pupal stage, tsetse emerges as adult flies. The adults are relatively large flies, with lengths of 0.5–1.5 centimetres (1⁄4–5⁄8 in), and have a recognizable shape, or bauplan, which makes them easy to distinguish from other flies.
Tsetse have large heads, distinctly separated eyes, and unusual antennae. The thorax is quite large, while the abdomen is wider, rather than elongated, and shorter than the wings.