A 40 million-year-old sex act is frozen in time

Forty million years ago, a female mite met an attractive partner, grabbed him with her clingy rear end and began to mate — just before a blob of tree resin fell on the couple, preserving the moment for eternity.

The discovery, reported in the latest issue of the Biological Journal of the Linnean Society, proves that some female mites are, or at least were, mightier than their mates.

Ekaterina Sidorchuk

A top view of the pair of mites that were caught in midcopulation for all time by a drop of tree resin.

Researchers Pavel Klimov and Ekaterina Sidorchuk studied the copulating mite pair, now preserved in Baltic amber. They noticed traditional sex roles were reversed.

"In this species, it is the female who has partial or complete control of mating," explained Klimov, an associate research scientist at the University of Michigan Museum of Zoology. "This is in contrast to the present-day reproductive behavior of many mite species where almost all aspects of copulation are controlled by males."

Mite sex is probably more complex and interesting than you might imagine for speck-sized creatures. In many present-day mite species, males coerce females to mate. The males fight off other potential suitors, and guard females before and after mating. If a partner isn't in the mood, too bad. Male harassment of females is common.

Female Glaesacarus rhombeus mites, however, evolved a pad-like projection on the rear end. This enabled them to cling to males and direct the mating process. Males of this species lacked the handy "butt grabbing" structure.

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Klimov said structures found in certain living mites show that not all modern female mites are subject to relentless harassment. These individuals also exert considerable control over the mating process.

He explained, "Some lineages have developed female copulatory tubes that function like a penis."