These pretty little bubbles are actually bug sperm

Springtails have evolved a rather strange way of mating. The males of these tiny soil-dwelling arthropods never actually get to meet their partners — instead, they deposit drops of sperm on sticks for discriminating females.

Male members of the springtail species, O. cincta, make no effort to meet females. Instead, they roam around leaves, pausing every now and then for a few seconds, leaving behind white stalks topped by globes that hold about 1,000 sperm (sounds suspiciously like my high school experience). These globules are covered in a shiny coating that preserves the sperm for up to two days.

As Susan Milius of Science News reports, this leads to some unconventional male-to-male competition. As biologist Zaira Valentina Zizzari points out, rivals search for sperm just to destroy it. And by destroy she means they eat it. Milius writes:

Given the rivalry, it wouldn't be surprising if males engaged in an arms race to produce more sperm stalks than their competitors. But Zizzari was surprised to discover that male O. cincta make fewer sperm packages when a competitor is sperm-dotting the neighborhood. Maybe he's enhancing the few he makes with extra sex appeal, Zizzari mused. To test the idea, she offered lab females a choice of globes from males with rivals or those made by an uncrowded guy.

Given the two options, "some females just sit and wait — and suddenly you see a female running to a sperm droplet and picking it up," Zizzari says. Others make the rounds of droplets on offer, gently touching them with their antennae. "Then she's not convinced, and she goes for another round."

Only 60% of females reached a decision within 15 minutes. Most of those who committed to the sperm then touched their reproductive tract opening to a droplet produced by a male troubled by a nearby rival.

More about indirect sperm transfer at Science News. And here's a link to Zizzari's study (pay-walled). Image via Zizzari.