Male giant water bugs win females by babysitting

There’s nothing like a guy doing all the child care to win female favor, even among giant water bugs.

Thumbnail-sized Appasus water bugs have become an exemplar species for studying paternal care. After mating, females lay eggs on a male’s back and leave him to swim around for weeks tending his glued-on load.

For an A. major water bug, lab tests show an egg burden can have the sweet side of attracting more females, researchers in Japan report May 4 in Royal Society Open Science. Given a choice of two males, females strongly favored, and laid more eggs on, the one already hauling around 10 eggs rather than the male that researchers had scraped eggless.

Females still favored a well-egged male even when researchers offered two males that a female had already considered, but with their egg-carrying roles switched from the previous encounter. That formerly spurned suitor this time triumphed.

A similar preference, though not as clear-cut, showed up in the slightly smaller and lighter A. japonicus giant water bug. “We conclude that sexual selection plays an important role in the maintenance of elaborate paternal care,” says study coauthor Shin-ya Ohba of Nagasaki University.