Insects have the ability to set how high above the ground they fly. The environmental cues used to set the “cruising height” of an insect have been debated. One model had postulated that insects determine their height based on optic flow, the rate of movement of objects below the insect in flight. However, sophisticated experiments designed to get a fruit fly to change its altitude in response to changes in optic flow were unimpressive.
Straw, Lee and Dickinson studied altitude preference in fruit flies and found that fruit flies fixed on a “local horizon”. Flies “fix” the visual system on the top of an object, (perhaps a bush or a wine glass) and adjust their height relative to the height of the object. This is convenient for flying insects such as fruit flies that often land on the tops of objects.
*Visual Control of Altitude in Flying Drosophila. Straw, Lee and Dickinson. Current Biology:20, Issue 17, 14 September 2010, Pages 1550–1556