We examined the effects of aerodynamic forces on the mechanical power output of running insects for which kinematic data were available. Drag and lift on the cockroaches Periplaneta americana (a small, rapidly running species) and Blaberus discoidalis (a larger, more slowly moving species) were measured in a wind tunnel. Although lift would be expected to affect power output by altering functional body weight, the magnitude of the lift on these cockroaches was less than 2 % of their weight. Drag, which increases the horizontal force that must be exerted to run at a given speed, accounted for 20–30 % of the power output of P. americana running at speeds of 1.0-1.5 m s-1, but had a much smaller effect on B. discoidalis. Aerodynamic drag on the body (parasite drag) can significantly increase the mechanical power output necessary for small, rapidly running insects in contrast to larger running animals and to flying insects.

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