The monstrous mandibles of a male stag beetle, while useful for mating, come back to bite him during transit.
Flying and running take considerably more work for a male Cyclommatus metallifer (left) than they would in a short-jawed world, computer simulations reveal. Saddled with the weight of his giant mouthparts, the beetle flies in an awkward, almost vertical position. The male gets hardly any lift from air pushing against his front (above, orange), and he must overcome diminished air pressure (blue) that sucks him backward. But the sorry aerodynamics have a lower energy cost to the beetle than does lugging his hefty mandible muscles, which account for about 18 percent of his body weight.
A male C. metallifer grows some of the most elongated mandibles among beetles. He needs them to fend off other males pursuing, of course, a female. Biophysicist Jana Goyens of the University of Antwerp in Belgium and colleagues used simulations based on scans of real beetles to quantify the energy cost of the mouthparts.
Reporting in the May 6 Journal of the Royal Society Interface, the researchers found that males use 26 percent more energy to fly and 40 percent more energy to run than they would with small, female-style mandibles.