Roving spider sailed 6,000 miles millions of years ago
Arachnid traded Africa for Australia across Indian Ocean
It’s smaller than a penny, but a spider native to Australia is an intrepid traveler, scientists say: It migrated to the land down under by floating across the Indian Ocean from Africa.
That’s about 6,000 miles. This species of spider doesn’t drift on silk balloons, as some spiders do, and it didn’t catch a ride with humans. So it must’ve made the trip on a chunk of land, according to a study published Wednesday in the journal PLOS ONE.
“The only hypothesis that fit is it came over by itself,” says study co-author Sophie Harrison, who analyzed the spider as a graduate student at the University of Adelaide in Australia. “It’s a hard thing to get your head around.”
The well-traveled arachnid is a kind of trapdoor spider, lying in wait for its prey in a burrow concealed with sticks, leaves and other debris. It’s gentle, shy and, despite its scientific name, Mog
gridgea rainbowi, plain brown. It lives on Kangaroo Island just off Australia’s south coast, but it looks almost identical to a trapdoor spider that lives in Africa. The logical explanation: The two spiders’ ancestors were separated when Africa and Australia — once joined along with other land masses in an enormous supercontinent — split apart 100 million years ago.
But after analyzing DNA from the Kangaroo Island and African spiders, Harrison and her colleagues realized the species’ forbears didn’t go different ways until 16 million years ago at the most. That’s tens of millions of years after Africa and Australia broke up.
So continental drift didn’t wrest the Australian spiders from their African relatives. Rather, they left. Other spiders are known to have rafted to virgin territory, but no other trapdoor spider traveled nearly as far as the Kangaroo Island arachnids, Harrison says.
There’s no telling how long the trip took, nor the size of the chunk of land that must have carried the spiders to their new home. Though small, the Kangaroo Island spiders are suited for arduous journeys. They can retreat into their burrows behind a tight-fitting door, and they can go months without food.
Evidence that other spiders drifted across the ocean to new lands shows that this spider’s trip “is not unprecedented,” Harrison says. But a trip of 6,000 miles, she says, is “pretty crazy.”