Hoverflies (probably) can’t sense gravity

Hoverflies not only defy gravity, they may not even know it’s there.

Insects known for their aerial acrobatics — like hoverflies and dragonflies — have to execute twists and turns with extreme precision. Whether they use gravity to orient themselves and control their altitude has been a mystery.

Rather than sending flies into space to test such abilities, Roman Goulard of Aix-Marseille University in France and his colleagues took a basic approach to simulating microgravity: Drop hoverflies (Episyrphus balteatus) in different lab environments and observe how the insects react to free-falling. In a dark box, hoverflies were slow to beat their wings and sense they were falling, and 70 percent crashed. In a light box, the insects had better reaction speed, but many still crashed. Finally, in a box with both light and striped walls (to create a visual pattern), they reacted quickly and crashed only 10 percent of the time.

Though impossible to rule out entirely, the insects don’t seem to have a means or internal organ (like mammals’ inner ear) to sense acceleration. Instead, hoverflies must rely on just sight and airflow to figure out where they are in space, the researchers argue August 16 in the Journal of Experimental Biology.