Sex can sometimes be awkward in humans, and sometimes painful, but rarely do human females have to put up with what females of the bean weevil endure. The male's penis carries a formidable array of sharp spines which lacerate the female reproductive tract during copulation.
These spines, say Helen Crudgington and Mike Siva-Jothy from the University of Sheffield, are the painful manifestation of reproductive conflict: For bean weevils, this is quite literally the battle of the sexes.
The bean weevil Callosobruchus maculatus is a small black beetle which infests stored grain, beans and pulses. Females lay their eggs on the beans, and the larvae hatch and eat their way inside. The fattened larvae pupate and emerge from the bean as adult beetles. From this time on they don't eat: Their only function is to reproduce.