How flies walk on ceilings

Walking upside-down requires a careful balance of adhesion and weight, and specialized trekking tools to combat the constant tug of gravity.

Each fly foot has two fat footpads that give the insect plenty of surface area with which to cling. The adhesive pads on the feet, called pulvilli, come equipped with tiny hairs that have spatula-like tips. These hairs are called setae.

Scientists once thought that the curved shape of the hairs suggested that flies used them to grip onto the ceiling. In fact, the hairs produce a glue-like substance made of sugars and oils.

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