How Can a Fly Walk on the Ceiling?
A fly can walk across ceilings because it has sticky feet. Each of the fly’s six feet are equipped with tiny claws and hairy pads, which give off a sticky liquid, a glue-like substance made of sugars and oils.
The sticky pads and claws enable the fly to cling to almost any surface. A fly usually stands on just four of its feet, but it uses all six when it walks. While walking, the fly picks up three of its feet at a time.
The other three hold the fly to the surface until it is their turn to move forward. In this manner, the fly is able to walk up walls and across ceilings without falling off.
Flies need sticky feet to walk on ceilings, but not so sticky that they get stuck upside down. So each foot comes with a pair of claws that help hoist the gooey foot off the wall.
Flies use several different techniques to get unstuck: pushing, twisting, and peeling its footpads free. Methods involving peeling are always the best, because they require less energy to break the contact.