To us humans, cannibalism seems like one of the stranger--and creepier--phenomena cooked up by nature. But eating one's own kind happens more often in the wild than you might think. Some animals almost seem to have evolved to be cannibals, some do it only through desperation, and some do it during their most passionate moments.

The Australian redback spider falls into this last category. During copulation the male often "somersaults" into the much larger female's mouth; two-thirds of the time she eats him, as seen here. His sacrifice pays off with greater copulation time and increased chances that the female will ignore future suitors.

Other male spiders are a little more careful. The goldenrod crab spider of Canada uses its silk-spinning abilities not to spin a web but to restrain the female during mating.