Why Insects Have Gay Sex

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Insect sex may seem fairly simple: fluttering dances, clasping abdomens, a quick mount on a forest floor. But a new review of homosexual insect encounters suggests the acts may not be that straightforward for the individuals involved.

Bugs. Bugs. Bugs. Lots of bugs -- the results from an eight-year-long census of a section of a Panamanian jungle.
DCI

Researchers have widely examined homosexual behavior in mammals and birds, but have addressed it less frequently in insects and spiders. To assess the range of evolutionary explanations for same-sex intercourse in the invertebrate world, a team of biologists from Tel Aviv University in Israel and the Swiss Federal Institute of Technology in Zurich, Switzerland examined roughly 100 existing studies on the topic and compiled the first comprehensive review of homosexuality in invertebrates. The review was published earlier this month in the journal Behavioral Ecology and Sociobiology.

The team focused on male-male interactions to simplify the analysis, and found that most of these encounters occurred as accidents. Whereas larger animals have developed more complicated homosexual motivations — like maintaining alliances, which has been found in certain primate and seagull species — insects seem to mistakenly partake in it in a hasty attempt to secure mates. [Gay Animals: Alternate Lifestyles in the Wild]

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"They have evolved to mate quick and dirty," said study co-author Inon Scharf, an evolutionary ecologist at Tel Aviv University. "They grab every opportunity to mate that they have because, if they become slow, they may give up an opportunity to mate."

In some cases, males carry around the scent of females they have just mated with, sending confusing signals to other perusing males. In other cases, males and females look so similar to one another that males cannot tell if a potential mate is a female until he mounts "her" and prepares for the act, Scharf said.

Sometimes, such extreme indiscrimination leads to mating with inanimate objects, as has been observed in beetles trying to mount glass bottles.

The glass bottle "looks like a huge female to them," Scharf said. "They just try to mate with whatever gives them a vague impression of an opportunity."

Other studies do, however, show evidence of more intentional and malicious motivations behind homosexual insect sex. Male butterflies, moths and wasps, for example, use same-sex encounters to distract competitors from potential female mates. Certain beetles have even been found to use same-sex mounting as a way to spread sperm to other males that may then pass it along to the next female he mounts, though this mechanism does not appear to be very effective.