These Australian Spiders Crossed an Ocean on a Land Raft

Today, this trapdoor spider is only found on a small island off the southern coast of Australia—but it undertook a long journey to get there. Nick Birks

If the idea of spiders sailing across the ocean gives you a fright, then there’s good news and bad news. The bad news is that this actually happened, according to a new report. The good news is that it happened millions of years ago, and now these spiders prefer to stay close to home—they spend their entire lives within just a few yards of their burrows.

Today, a small trapdoor spider, Moggridgea rainbowi, is only found on Kangaroo Island, off the southern coast of Australia. They make silk cocoons in underground burrows, where they wait for food to wander by. But the trapdoor spider’s nearest relatives live more than 6,000 miles away, across the Indian Ocean in South Africa. Scientists have long thought the species must have split off from the family tree when Africa separated from the supercontinent Gondwana, about 95 million years ago. But after analyzing specific gene sequences, researchers from the University of Adelaide determined that the split actually happened between 2 and 16 million years ago. But that was before humans were around to ferry species across open water. This leaves just one other option.

The last theory standing posits that the spiders were stowaways on a land raft—a chunk of land or vegetation that washed out to sea, a little drifting island ecosystem that, eventually, ended up on the other side of the Indian Ocean. “The burrows they live in are quite stable and they would have been quite secure in their silk-lined tubes with their trapdoors closed—it was probably quite a safe way to travel,” said Sophie Harrison, the lead author of the report, in a press release. It’s not so far-fetched; other related species live on islands a couple hundred miles from the coast of Africa. Fortunately for arachnophobes, they’re no longer globe-trotters.

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