Valentine Alert: Male Insects Seduce With Fake Finery

Hillary Mayell
for National Geographic News

February 14, 2005

Ladies: If you're looking for diamonds on Valentine's Day, be careful that your beau isn't giving out fakes. Scientists have found that, even in the animal kingdom, males hand out so-called nuptial gifts that seem to be worthless.

Nuptial gift giving is a well-known phenomenon. Gifts frequently consist of food like nutritious prey items or dried insect fragments. The female typically eats her gift while copulation takes place.

"Insects and spiders are well known for giving presents," said Steven Heydon, senior museum scientist and collections manager at the Bohart Museum of Entomology at the University of California, Davis. "Some species always give a gift, some never give a gift. Some males just give a drop of saliva; it's basically just a little treat to keep her busy while mating goes on."

However, scientists have also observed that among some species in which males bring a nuptial gift they're getting away with bringing large, highly visible, but worthless gifts like seed tufts and silk balloons.

"Males take some risk in hunting for a gift; they could be eaten by a bird or become prey themselves," Heydon said. "Also, the time they spend hunting can't be spent mating, so the evolution toward useless presents is more of an advantage to the male."

Two biologists at the University of St. Andrews in Scotland set up a series of experiments using a species of dance fly, Rhamphomyia sulcata, to try to figure out why females would require a worthless gift as a precondition to mating.

They found that the female dance flies that received the largest nutritious gifts copulated for a significantly longer amount of time than when given either a small nutritious gift or a larger worthless one. Longer copulation time would increase the male's chances that his sperm would be used to fertilize her eggs.

The females copulated for a shorter time when given a small nutritious gift. But the researchers found that worthless tokens were worth as much as small valuable gifts, at least from the male perspective. Each of these two types yielded the same amount of mating time.

Assuming the shorter copulation time still allowed the male to transfer sperm, it may be to his advantage to bring an easily obtainable worthless gift and mate more frequently, albeit for shorter amounts of time.

"These findings suggest that female behavior in genuine gift-giving species is susceptible to the invasion of male cheating on reproductive investment," Natasha R. LeBas and Leon R. Hockham conclude in a recent study published in the journal Current Biology.

Building a Scientific Experiment

Lebas and Hockham needed to make sure that the female dance flies were responding to the biggest nutritional gifts, and not some evolutionary response to mate with males who have the largest bodies—and can therefore bring the largest gifts.

Male and female dance flies meet in a common area during breeding season to mate, a phenomenon known as lekking. Pairs form in the lek and then descend to mate on the surrounding vegetation. The researchers followed the pairs to where they landed.

Thus assured that the pairs had just begun copulation, the scientists substituted four gifts on a rotating basis: large nutritious gifts (in this case, almost-whole prey insects), large worthless tokens (balls of cotton wool), small nutritious gifts (fragments of prey insects), and small useless tokens (tiny bits of cotton wool).

Though the switching of gifts was tricky—with a 20 percent success rate—the scientists noted that the females had to have hold of real gifts or substitutes. Otherwise, they immediately stopped mating.

Timing of the copulation began as soon as the female accepted the substitute gift.

The Ultimate Sacrifice

Of course there are some species where the females won't be fooled by tawdry offerings. Among some cannibalistic species in which the female is larger and more predatory than the male, the females require the ultimate sacrifice.

"There's some evidence the female has to eat the head of the male mantid to release the full complement of mating behaviors," Heydon said. "In other words, they can't do it unless he loses his head."

When the male loses his head—literally—it blocks normal inhibitory nerve impulses, and he becomes more enthusiastic sexually, at least from a physical point of view. Bizarre as it seems, the male mantid can continue to engage in sex after his head has been devoured.

Sexual cannibalism isn't an absolute requirement for the mantis to reproduce. If the male can successfully sneak up on the female, jump on her back, and afterward retreat successfully, he lives to see another day. It's during approach and departure that he is vulnerable.

The advantage of mate eating for the female may be that it provides a conveniently handy source of protein for herself and her offspring.

Females in more than 80 other species have been known to eat their mates before, during, or after mating.

In her book on the evolutionary biology of sex, titled Dr. Tatiana's Sex Advice to All Creation, Olivia Judson writes about the mating habits of midges.

"The female captures her mate as she would any old prey and plunges her proboscis into his head while they link genitalia. Her spittle turns his innards to soup, which she slurps up, drinking until she's sucked him dry, then dropping his shell. only his manhood, which breaks off inside her, betrays the fact that this was no ordinary meal."

Keep that in mind, fellas, when you're out shopping for your sweetheart today.

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