When beetles brawl, they put professional wrestlers to shame. Male Cyclommatus metallifer stag beetles use their long jaws, called mandibles, in scuffles for rotten wood and mating rights (as seen in the above video). During a bout, the beetles maneuver their opponent between their pinching pincers and try to flip them helplessly upside down. Scientists wondered why beetles touting larger mandibles win more fights even though their long jaws should transmit less force to the pinching point, significantly reducing the strength of their grip. Wrestling with this issue, a team of researchers tested the crunching force of male and female stag beetles. While female stag beetles have tiny nublike mandibles, the team found that females gripped with one-sixth the force of their male counterparts. Even accounting for differences in body size, male beetles still clenched three times harder. CT scans revealed that the muscle responsible for closing the mandibles is almost four times larger in males and that the lever connecting this muscle to the mandibles is three times larger, the researchers report online today in The Journal of Experimental Biology. The team says that male stag beetles adapted their head shape to accommodate the longer muscles and levers, allowing them to wield their ungainly weapons and become the undisputed wrestling champions of the insect world.
(Video credit: Jana Goyens/University of Antwerp)