For some animals, sex seems more like an act of war.
In a diverse array of species—including worms, spiders, snails, and bedbugs—the male stabs the female with his penis, injecting sperm directly into her body cavity.
This bizarre mating strategy is called traumatic insemination—and now there's another species to add to the list of tormenters: a parasitic insect called Stylops ovinae.
Hans Pohl, of Friedrich Schiller University Jena in Germany, and colleagues analyzed S. ovinae's sex lives in detail for the first time using high-resolution microscopes and other sophisticated imaging technology.
Like other species of twisted-winged parasites, male and female S. ovinae lead very different lives. Males, which live mere hours, fly around looking for females.
Females, meanwhile, are busy parasitizing other insects, such as bees: Almost all of their tiny bodies are hidden inside the abdomens of their hosts. With no need to move, females lack wings, eyes, antennae, legs, and genitalia.
To get around this problem, the male attaches to the host insect’s abdomen and then stabs its hook-shaped penis into the female’s pinhead-size neck. He injects his sperm into her body, fertilizing the eggs that float in her hemolymph—the insect equivalent of blood.
Motherhood is no less grisly: A few weeks later, the larvae leave their mother after virtually eating her alive, according to the study, published recently in the journal Scientific Reports.
Until now, scientists assumed that S. ovinae's mating took place via the female’s birth canal, without any stabbing involved.
But Pohl and his colleagues discovered that females possess a specialized invagination, or fertilizing pocket, on their neck region, where males inject their sperm. Having this "pocket" likely reduces the chance the female will be injured.
“This is a really elegant and clever study that adds a new piece of evidence to what we know about traumatic insemination," says Michael Siva-Jothy of the U.K.'s University of Sheffield, who was not involved in the research.
Gettin' It On—For a While
It turns out the wings aren't the only things twisted about this parasite—its sex life is pretty kinky, too. S. ovinae couples invest an unusually long time in the act, the study found.
The team observed 227 mating sessions that ranged between two seconds and more than 30 minutes, averaging about eight minutes—a long time for an insect.
This is likely the male's doing: Prolonged matings may reduce the chance that the female received sperm from other males.
Indeed, Pohl and his colleagues found that males are able to detect if a female has already mated with another male.
“The second mating with the same female is significantly shorter, and the duration decreases further when a second male mates with an already mated female,” says Pohl.
Pohl says that it is likely that all 6,000 species of twisted-winged parasites use traumatic insemination, which has persisted for millions of years and evolved multiple times in different animal lineages.
Exactly how it helps a species survive is not yet clear.
“Some males may benefit because they may have easier access to female [eggs],” Siva-Jothy says.
“And while the costs to females are often associated with wounding and infection, some studies have shown there may be benefits, as well. For instance, in bedbugs, males transmit compounds that increase the female’s ability to lay eggs."