Male butterflies plug attractive females’ genitals to stop them mating

Some male butterflies plug up their mates’ reproductive tracts to prevent them from having sex with rivals. Now, there’s evidence that they might not be doing so indiscriminately. The type and size of the mating plugs seems to correlate with how much males are willing to invest in their partners.

Males of several groups of animals, such as beetles and water bugs, are known for mate-guarding: sticking around after copulation to keep others away from their partner and increase the chance that they alone will …