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A few days after leaving their larval skins, black-tailed skimmers (Orthetrum cancellatum) in Hungary rest on a twig as their bodies harden. While still soft—called the teneral stage—the dragonflies are vulnerable to predators, especially birds.

He pulls the male out of the net and turns him upside down to look at his genital organs.

At the tip of the male's abdomen are its testes; at its base, behind its legs, is a penis and a small swollen pouch for storing sperm. Male dragonflies sport two sets of sex organs, the prerequisite equipment for a mating system that is unique in the insect world. Before he copulates, a male dragonfly must in essence self-inseminate, moving his sperm from the testes to the storage pouch and into the penis. Here comes the tricky part. He must grip a female by the head or thorax and hold her in the tandem position, with claspers at the tip of his abdomen that fit neatly, like a lock and key, with a special plate on her thorax or behind her eyes.

"If it seems that dragonfly biologists are inordinately preoccupied with sex, they may be excused," Corbet says. Sexual behavior is key to understanding how dragonfly species got to be the way they are. And sexual organs are key to their identity. "Slight differences in this clasperplate system are what define some species that are otherwise nearly impossible to distinguish."

Once the pair is in tandem, and the female is receptive to the overtures of her suitor, she will curl the tip of her abdomen around to bring her vagina in touch with his penis, working the pair into that heartlike copulatory position.

"It's a jolly difficult business," says Corbet, "and there's much speculation about how it evolved." Some experts believe that the male originally placed his sperm package on the ground. This was risky, given what Corbet calls the "predatory proclivity" of some female dragonflies to banquet off their partners. Males may have adopted the tandem position to protect themselves from becoming their lovers' prey. Over the ages they evolved ways of keeping their sperm packages safely tucked under their abdomens and, eventually, a complex genital "sperm bank" for storing it there.

So, too, they evolved strategies for effectively guarding their mates and fending off rivals. After sex, many pairs do not disengage but fly about in tandem, the male guarding the female by continuing to grasp her while she lays her eggs. This may serve the female, protecting her from clamoring suitors so she can oviposit in peace.

But there's nothing chivalrous about male sexual behavior. Some males embrace females with spiny claspers in a viselike grip that causes damage. Look closely at the eyes of a female darner, and you may well see dark puncture marks. This sort of abuse appears widespread among some dragonflies. In one study of 12 species of clubtails by Sidney Dunkle, a biologist then at the University of Florida, 88 to 100 percent of all females had holes in their heads, caused by a male's iron hold. The aptly named dragonhunter (Hagenius brevistylus) earned the dubious distinction of inflicting more severe damage than any other dragonfly: The spines of his appendages gouged the female's eyes, punctured and split her exoskeleton, and pierced her head, so that a "maximally damaged" female had as many as six holes of varying sizes punched in her head.

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