What elastic protein helps power the jumps of fleas?

The elastic protein that helps power flea jumps is resilin.

Resilin is a rubber-like protein embedded in specialized regions of the insect cuticle. In fleas, resilin-rich pads in the thorax and near the bases of the hind legs deform as the flea crouches. Muscles load this elastic system, and a latch-like mechanism releases the stored energy rapidly, producing the flea’s explosive takeoff.

This arrangement solves a mechanical problem: muscles alone cannot contract quickly enough to generate the force of a flea’s jump in the brief launch interval. Elastic storage allows muscle work to accumulate before being released almost instantaneously. Resilin is also used elsewhere in insects, including wing joints, sound-producing structures, and other spring-like mechanisms.

The answer does not mean resilin is the only material involved. The flea’s stiff cuticle, muscles, tendons, joints, and locking mechanism all contribute to the jump. Modern biomechanical studies also debate how much energy is stored specifically in resilin versus chitinous cuticle, but resilin remains the canonical elastic protein associated with flea jumping.