How do resilin pads help fleas leap?

Fleas utilize resilin, a highly elastic protein, to achieve their remarkable jumping ability. Although fleas are wingless, they have retained the resilin hinge originally associated with insect flight mechanisms, repurposing it at the site where their legs attach to the thorax.1

When a flea prepares to jump, it crouches, compressing these resilin pads. This state is held by a muscle-controlled catch mechanism. When the flea is ready to leap, the catch muscles relax, allowing the stored energy in the compressed resilin to be released rapidly. This energy is transferred through the legs, creating a powerful lever effect that pushes the tibia and tarsus against the ground, propelling the flea into the air. This mechanism allows them to achieve accelerations of 200 gravities and leap distances up to 200 times their body length.1