Field and laboratory experiments were carried out in Ghana on the tsetse fly, Glossina medicorum Aust., to discover the senses used by the fly in finding its host. In laboratory experiments on vision a model locomotive with a black screen attached to it was used as a ‘host’. The flies were stimulated to move by the movement of the screen. When the screen was stopped and started for short periods the increase in activity became less each time the screen was put in motion but the fall off was less rapid than in experiments with continuous movement. The possible significance of this is discussed in the light of the normal habitat of the species in the field.

In the field, G. medicorum did not respond to a moving object more than 25 ft. away but G. morsitans Westw. showed a good response at distances up to 150 ft.

Tethered flies were attracted to the model screen and showed a preference for landing on the lower edge near the centre.

Laboratory experiments using a guineapig and a goat as sources of smell produced no response from the flies but a strong reaction was obtained with the vapour of dilute acetic acid. In field experiments, using cows which were not visible to the fly, a very marked response to the smell of the cows was obtained. Orientation to a source of smell probably involves orientation to air movement and G. medicorum showed a strong upwind orientation in a wind tunnel even when blinded.

It is concluded that G. medicorum, which lives in thicket or forest where visibility is poor, probably responds initially to the smell of a potential host. An upwind orientation would then bring it to the general vicinity of the animal and the final approach might be visual.