Rove beetles have come up with a truly novel way to ensure monogamy. After a male has mated with a female, he injects her with a chemical that makes her smell so bad that all other prospective suitors stay away.
We recently reported on one of the few actual aphrodisiacs ever discovered in nature. Well, the rove beetles use an anti-aphrodisiac, which makes other males lose interest in trying to mate with the female. For the original male, that's a huge reproductive benefit, as rove beetles are one of many insect species in which the female can theoretically be impregnated by multiple males simultaneously.