Reproduction is a driving force across the animal kingdom, with creatures developing diverse strategies to ensure their genes are passed on.
Some male butterflies employ a unique technique - they force the female into a 'chastity belt' that prevents her from reproducing with other suitors.
In response, some females seemed to have evolved larger, more complex genitalia that are harder to block.
The result has been an all-out battle of the sexes, with males devising increasingly ornate mating plugs -some with winglike projections, slippery scales or pointy hooks.
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Mating plugs are found in just one percent of butterflies. Simpler plugs may be torn or ripped off by a determined female, but in species with large, complex plugs, researchers rarely encountered a female without one
A female butterfly fertilizes most of her eggs with sperm from her last partner, so its to the male's benefit to block access to rivals.
But external mating plugs, also known as sphragis, are found in just one percent of all butterflies.
Other species employ sphragis, including kangaroos, bees, rats, spiders and several kinds of primates.
Typically they ensures paternity, but they can have other benefits for butterflies, too: The Rocky Mountain parnassian's mating plug delivers protein to the female.
Researcher Ana Paula dos Santos de Carvalho with butterfly samples at the Florida Museum of Natural History's Kawahara Lab. Carvalho says she was surprised to see the sphragis didn't play a bigger role in the development of new butterfly species
Some male butterflies produce a sphragis, or mating plug, that prevents his mate from reproducing with other suitors
The zebra longwing butterfly's sphragis includes predatory defense chemicals and an anaphrodisiac that turns off other males.
While the female will eventually expel the plug, it may be in place long enough for a male to ensure his sperm have reached the egg and achieved fertilization.
Rather than use a mating dance or song, a plug-producing male butterfly will grab a female in midair and drag her down to the ground.
After depositing his sperm, he excretes a pre-molded plug from intricate abdominal ducts that give it its shape.
It then hardens on the female, blocking her