NOEL KING, HOST:
Alien invaders have colonized an island near Antarctica. They landed there in the 1960s and dug deep into the soil. They've been reproducing and spreading. Scientists say they seem to be changing the island's environment and worry they'll infest Antarctica's mainland. NPR's Christopher Joyce explains what's going on.
CHRISTOPHER JOYCE, BYLINE: Ecologist Jesamine Bartlett says the invaders pretty much own the island of Signy.
JESAMINE BARTLETT: It's the largest terrestrial organism on the island.
JOYCE: How large? Well, maybe a third of the size of a ladybug. They're midges - miniature flies. Normally, they live only on South Georgia Island hundreds of miles away, but researchers in the 1960s moved some plants from South Georgia to see if they could survive on Signy. They didn't, but the bugs on the plants managed to hang in there.
BARTLETT: These are really extreme environments we're talking about. Not much tends to get there, and not much tends to survive there. And this thing has done both, and not only that, it's thriving.
JOYCE: The midge doesn't even need mates. It reproduces solo, asexually.
BARTLETT: It doesn't have any predators. It doesn't have any competitors. So it's been able to just set up camp there and spread around.
JOYCE: The midges like moss, which is good for them because it's mostly what grows on the island. Bartlett, at the University of Birmingham in Great Britain, says the midges decompose organic material in the soil.
BARTLETT: It's effectively doing the job of an earthworm in an ecosystem that's never seen anything like it.
JOYCE: So what's the harm here? Well, their appetite is altering the island. They create huge amounts of nitrogen compounds. It's like dumping fertilizer in the soil. And it could change the mix of plants and other insects there. Peter Convey from the British Antarctic Survey says that the midges might reach the Antarctic mainland and play havoc with the ecosystem of one of the world's last pristine places.
PETER CONVEY: Basically, the cat's out of the bag. Invading species are affecting everywhere, more or less. And Antarctica is the last sort of continental scale part of the world where this isn't the case.
JOYCE: Convey says scientists are doing their best to keep the midges from migrating off the island. Christopher Joyce, NPR News. Transcript provided by NPR, Copyright NPR.
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