How are fleas adapted for jumping?

Fleas are remarkably adapted for jumping through a specialized mechanism that repurposes components of the ancestral flight system. Although fleas are wingless, they have retained a hinge made of resilin, a highly elastic protein that typically assists with wing strokes in flying insects.1

When a flea prepares to jump, it crouches, compressing these resilin pads. This energy is held in place by a muscle-controlled catch mechanism. Upon release, the stored energy is rapidly transferred through the legs, creating a powerful lever effect that pushes the tibia and tarsus against the ground.1

This mechanism allows the flea to achieve incredible acceleration—up to 200 gravities—and leap distances up to 200 times its body length. During the jump, the flea's body is tilted upward by the middle legs, while the hind legs swing backward to propel the insect forward at an angle of approximately 50°. Because of this extraordinary ability to generate force and distance, fleas are often described as insects that "fly" with their legs.12