Invasive asexual midges may upset Antarctica’s delicate moss banks

Some of the scariest poop in Antarctica comes from an all-female invader species about the size of an ant. Researchers are now fretting about what the waste from these debris-eating midges may do to the continent’s once nutrient-sparse moss banks.

The midge Eretmoptera murphyi, a kind of tiny fly that can’t actually fly, hitchhiked onto the Antarctic island of Signy probably sometime in the 1960s during plant-introduction experiments that would never be allowed today. In moss banks where the alien midges now thrive, their excretions boost nitrogen concentrations to levels similar to those where seals come ashore, says Jesamine Bartlett, a polar and alpine ecologist at the University of Birmingham in England.

She has calculated that the hard-to-spot midges triple or quadruple the usual nitrogen in moss banks, which seals don’t visit. Bartlett, who also works with the British Antarctic Survey in Cambridge, reported the results December 19 in Birmingham at the annual meeting of the British Ecological Society.

The midges are a shock to the ecosystem because Antarctica doesn’t have the usual earthworms and other voracious detritus-feeders that quickly break down dead plants and other organic debris, like the midges do. So the insect “has the potential to change the way the ecosystem functions quite drastically,” says systems ecologist Peter Convey, also of the British Antarctic Survey, who collaborates with Bartlett. Extra nutrients could, for instance, offer opportunities to more invaders.

These disruptive midges may not be native to Antarctica, but they “are tough as anything,” Bartlett says. Typically found in the subantarctic island of South Georgia, they can withstand freezing solid in a block of ice. When the ice thaws, the midges soon start wriggling again.

Conveniently for the invaders, these midges are an all-female species. “You only need one lady to be dropped off” for a population to get a foothold, Bartlett says. If conditions are turning harsh, a female can lay her big, jellylike glob containing 40 to 50 eggs even before fully emerging from her own pupal stage to adulthood.  

The eggs she lays typically need about two years to reach motherhood themselves. Eggs hatch in about a month into the first of four larval stages with a soft wormy body, often yellow from its nutrient stores of lipids, a hard head capsule and eye pits for rudimentary visual tasks. When larvae eventually graduate to the final pupal stage and grow an adult body, the high-priority gonads form early. In a late stage, the pupae in their protective cases take on a crusty look “as if they’ve been tempura fried,” Bartlett says. Legs come free of the pupal case before full adulthood, allowing a pupa to crawl around. “I found it quite alarming the first time I saw it,” she says.

If the mere specks of larvae hitchhike unnoticed on boots and establish themselves in other parts of Antarctica, there could be “serious repercussions,” says ecologist and invasion biologist Melodie McGeoch of Monash University in Melbourne, Australia, who isn’t part of the midge study.

Warming due to climate change may create new homes for midges in Antarctica, making the invasion even more of a cause for concern. Ice-free patches could expand by more than 17,000 square kilometers by 2100, close to a 25 percent increase, a 2017 study in Nature predicted. That estimate does use a pessimistic warming scenario, says Jasmine Lee of the University of Queensland in Brisbane, Australia, one of the authors on the study in Nature. However, she adds, it’s “the one the globe is currently tracking.”