The Friends of Charles Darwin

A male meadow vole faces a big problem: How can it become a father when a female meadow vole is likely to mate with every other male in the neighborhood?… Tactics vary enormously. The penis of the male black-winged damselfly, for example, is adapted to act like a scrubbing brush. It can remove up to 100 percent of previously deposited sperm. This option isn't open to the male meadow vole, or any other mammal. But a new study, published tomorrow in the science journal Nature, suggests the male vole employs another ingenious tactic: It uses its nose to sniff out potential rivals. If they are detected, the male reacts by unleashing an extra dose of sperm while mating.