To enhance the probability of reproductive success, interesting behaviors have evolved in the insect world among males, including the removal of a rival's sperm by elongated and otherwise interestingly-shaped genitalia.
Once a male damselfly finds a female to mate with, he will do anything to hold on to her. Literally. He will clasp the female damselfly behind her head and carry her around to prevent her from mating with another male.
In some species, the male will scoop out from the female's reproductive tract the sperm of the male she previously mated with and only then will he deposit his own. For this purpose, the male's penis has spines.