Photograph by Scott Henderson

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Two gold swift moths demonstrate one of their unusual mating positions.

Photograph by Scott Henderson

Bug Kama Sutra: Flexible Moth Evolved Many Ways to Mate

Every day is Valentine's Day for the gold swift moth, which may have the most advanced mating system of any bug.

When Pope Gelasius of Rome declared February 14 to be St. Valentine's Day about 1,500 years ago, he probably didn't know about the surprisingly romantic acrobatics of the gold swift moth (Phymatopus hecta).

The impressive species, native to northern Europe and Asia, has the most elaborate mating system so far known in insects.

Not only does the moth choose from several courtship strategies, the flexible critter also employs various sexual positions, offering up a sort of Kama Sutra for bugs.

According to biologist John R. G. Turner of the U.K.'s University of Leeds, most moth species have a very simple mating method that lacks any real courtship.

"Females stay perched where they are [after emerging from the cocoon], emit a pheromone that males can detect, and mate with the first male that turns up, said Turner, who recently published a study on the moth's sex life in the Biological Journal of the Linnean Society.

Not so for the gold swift, which has "at least seven different courtship patterns," explained Turner.

Sex With a Hint of Pineapple

Those patterns include what's called a "lek," which is when males gather together to court females en masse, rather than going it alone.

Each male in the group displays by vigorously hovering or by perching on the top of vegetation with wings spread and bright yellow scent brushes dangling.

The scent brush is a cluster of chitin "hairs" (more like scales) on the backs of males' lower legs. The hairs hold the pheromone scent—which, Turner says, "smells strongly of pineapple."

Females fly in, drawn by the sweet perfume, and take their pick of the performers. (Take our Valentine's Day quiz.)

But in contrast to lek systems of other animals, gold swift females aren't limited to that strategy—they can also still emit their own pheromones, allowing them to lure rather than be lured.

Gold swifts also sometimes opt for the mutual and "delightful" courtship dance in which a pair hovers together for a time before perching to complete the act, Turner said.

Flexible Flirting

What's more, despite relatively simple brains, a gold swift moth "can make a last-minute 'decision' about which courtship procedure to use," Turner said.

The choice is based on who detects whom first, what the other moth is doing, and so on, he said. "It's not unlike the back-and-forth flirting between people at a club or bar."

And they're also flexible in other ways. Though the moths remain perfectly still when mating—to avoid detection by bats—they mix things up a bit by having a choice of sexual positions. (Also see "Small Squid Have Bigger Sperm—And Their Own Sex Position.")

For instance, sometimes the moths will be face-to-face when they join the tips of their abdomens (where moth genitalia are situated).

Other times, the bugs will do it "back to front," with the male facing away from the female, "which I'm pretty sure is absolutely impossible in humans," said Turner.

What's Not to Lek?

So how did the moths evolve such a mating smorgasbord? (Also see "Wild Romance: Weird Animal Courtship and Mating Rituals.")

There's no consensus on how the lek system—which has been studied most in birds—evolved. But these moths, Turner says, paint a relatively simple picture.

Long ago, when females began congregating in places that were safe to mate, males adapted by arriving in those places early, scent brushes at the ready, in anticipation.

For swift moths, then, this may be how the lek—like a fraternity, single girls invited to a party full of boys—was born and bolstered over time.

But the rules of that system bend nicely for female swift moths. By being able to tap behaviors from along an evolutionary continuum, rather than sticking to a fixed pattern, they have evolved a superbly efficient pickup strategy.

"A female that doesn't find a male one way," Turner says, "is very likely to find him in one of the other ways, and quickly."

The final lesson from the swift moth's reproductive repertoire, then, may be that the evolution of lek behavior is less about picking the perfect mate and more about developing efficient ways to get the sexes together in one spot.

After all, says Turner, "you can't choose between brands of cereal if you never get to the supermarket in the first place."

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