The male Zeus bug at about 1mm in length and half the size of the female will piggy-back on his female mate, seating himself comfortably in a seemingly custom-made hollow. During the ride, the male sups on an all-you-can-eat protein-packed wax the female secretes from a gland near her head. All that remains for the male is to get down to the serious business of mating with the female. “The female usually produces the wax feed when a male is riding her and she will continue to produce it for as long as the male remains, yet once deposited, his sperm will allow her to continually produce batches of fertile eggs for up to two weeks,” he says.
The female’s gift is highly unusual in evolutionary terms. Across the animal world, it is traditionally the male who brings food offerings to the female as part of the courtship ritual or during mating. The theory behind this is that “nuptial gifts” make evolutionary sense: by making the female stronger and healthier with the food, the male is investing in his unborn offspring.
But this argument is unlikely to hold true in the case of female gifts, the authors said.
In the case of the Zeus beetle, the food may be a simple act of survival — to prevent the female from being gobbled up by the starving male after sex. “Our results indicate that female gift giving is not necessary to ensure a regular sperm supply,” the authors said. “Instead, it may have evolved to reduce costs imposed by males, in the form of cannibalism, kleptoparasitism and other forms of interference.” If so, the findings are remarkably appropriate. The beetles are named after the Greek god Zeus, who consumed his first wife, Metis.
The study, published on July 24 in the British weekly science journal Nature, was led by Gran Arnqvist of the Department of Animal Ecology at Sweden’s University of Uppsala.