How do flies and other insects walk up walls without falling?
Numerous insects, such as common houseflies, as well as certain amphibians and reptiles (tree frogs and geckos, for example), are able to walk on and cling to seemingly smooth surfaces--including glass doors and windows.
This trick is accomplished not by suction cups or adhesives but rather by a large number of tiny bristles or hairs on the bottom surface of the animals' feet. Scientists have produced scanning electron microscope images of these bristles. Surfaces that appear perfectly smooth to us actually have many microscopic bump and fissures, which serve as footholds for the tiny hairs.