The Beatrix gold mine lies a few hours outside of Johannesburg, South Africa, in one of the richest gold fields in the world. It extends more than two kilometres underground and every year, 10,000 workers extract around 11 tonnes of gold from the mine. But recently, something living came up with the gold, a creature that has been named after Mephisto, the Devil from the Faust legend.
So far, this seems like something from a stock fantasy tale, where miners dig “too greedily and too deep”, and release an ancient unspeakable evil. Fortunately, the creature that lurks in the Beatrix mine – Halicephalobus mephisto –is just a worm, barely half a millimetre long. It’s no demon of shadow and flame, but it is an incredibly surprising find. It’s an animal that lives where no other animals were thought to exist, in the rocky underworld known as the “deep subsurface”.
The deep subsurface refers to anything deeper than 8 metres, below than the reach of rabbit warrens and tree roots. It is a hot, cramped world, high in pressure and low in oxygen, a far cry from the sun-drenched, wind-swept surface. But it’s also teeming with life. There are more microbes in the subsurface (bacteria, and the extreme archaea) than there are up top, and collectively, they might even outweigh all surface life. Put every tree, elephant and human on a giant scale, and they’d be balanced by the microscopic masses that lurk underground.
Animals must wage a never-ending war against parasites, constantly evolving new ways of resisting these threats. Resistance comes in many forms, including genes that allow their owners to shrug off infections. But one species of fly has developed a far more radical solution – it has formed a partnership with a bacterium that lives in its body and defends it against a parasitic worm. So successful is this microscopic bodyguard that it’s spreading like wildfire across America’s besieged flies.
The fly Drosophila neotestacea is plagued by a nematode worm called Howardula. Around a quarter of adults are infected and they don’t fare well. The worm produces thousands of young in the body of its hapless host, and the little worms make their way into the outside world via the fly’s ovaries. Not only does this severely slash the fly’s lifespan, it also always sterilises her. But according to John Jaenike from the University of Rochester, the fly is fighting back.