Dragonfly sex is a rough and tumble affair. If you've ever seen a pair of mating dragonflies in the throes of passion, you know that their sexual coupling requires the flexibility and acrobatic skill of a Cirque de Soleil performer. Females get bitten, males get scratched, and sperm winds up everywhere. These strange mating habits have survived millions of years of evolution, so the dragonflies must know what they're doing, right? Let's take a closer look at how dragonflies mate.
As you might imagine, dragonflies don't engage in elaborate courtship rituals. In a few families, the male dragonfly may display his colors, or fly over his territory to show a potential mate what a good oviposition site he's chosen for their offspring, but that's about it. Dragonfly foreplay leaves much to be desired.
Because dragonflies have extraordinarily good vision, the males rely mostly on their eyesight to find appropriate female partners. Since a typical pond or lake habitat will support many species of dragonflies and damselflies, he must be able to distinguish females of his own species from all the other Odonates flying around. A male can recognize a conspecific female by observing her flight style, her colors and patterns, and her size.
As with many insects, male dragonflies make the first move to initiate sex. When a male spots a female of his own species, he must first subdue her. He'll approach her from behind, usually while they are both in flight, and hold onto her thorax with his legs. If he's feeling feisty, he might bite her, too. If he hopes to mate successfully, he must get a firmer grip on her quickly. The male dragonfly will pull his abdomen forward and use his anal appendages, a pair of cerci, to clasp her by the neck (her prothorax). Once he has her tightly by the neck, he can extend his body and continue to fly with her, in tandem. This position is known as tandem linkage.
Now that he's got a hold of a mate, the male dragonfly needs to prepare for sex. Dragonflies have secondary sex organs, meaning they don't store sperm near the copulatory organ. He must transfer some sperm from a gonopore on his ninth abdominal segment to his penis, which is located under his second abdominal segment. Once he's charged his seminal vesicle with sperm, he's ready to go.
Now for the acrobatics. The female's genital opening is near the tip of her abdomen, while the male's penis is closer to his thorax (on the underside of his second abdominal segment). The female must bend her abdomen forward, sometimes with coaxing from the male, to bring her genitalia into contact with his penis. This position during copulation, known as a wheel formation because the couple forms a closed circle with their joined bodies, is unique to the order Odonata. In dragonflies, the sex organs lock together briefly (not so for damselflies). Some dragonflies will mate in flight, while others will retire to a nearby perch to consummate their relationship.
Competition Among Male Dragonflies:
Female dragonflies operate by the "last in, first out" rule of fertilization. If given the opportunity, she might mate with multiple partners, but the sperm from her final sexual partner will fertilize her eggs, in most cases. Male dragonflies, therefore, have an incentive to make sure their sperm is the last to be deposited in her.
A male dragonfly can increase his chances of fatherhood by destroying the sperm of his competitors, and he's well equipped to do so when he mates. Some dragonflies have backwards-facing hooks or barbs on their penises, which they can use to scoop out any sperm they find inside their partner before depositing their own. Other dragonflies use their penises to tamp down or move the offending sperm, pushing it aside before he places his own in the ideal location for fertilization. Still other dragonfly males will dilute any existing sperm they find. In all cases, his goal is to ensure that his sperm supersedes that of any prior partners she has had.
Just to provide an added measure of security for his sperm, the male dragonfly will often guard the female until she oviposits her eggs. He tries to prevent her from mating with any other males, so his sperm is assured the "last in" position that will make him a father. Male damselflies will often continue to grasp their partners with their cerci, refusing to let go until she oviposits. He'll even endure a dunking in the pond if she submerges to place her eggs. Many dragonflies prefer to guard their partners by simply chasing off any approaching males, even engaging in wing-to-wing combat if necessary.
- Dragonflies and Damselflies of the West, by Dennis Paulson.
- Encyclopedia of Insects, 2nd Edition, edited by Vincent H. Resh and Ring T. Carde