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By Amanda Greenwood
Associate News Editor
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A newly identified species of trapdoor spider, a burrowing spider known for building concealed doors over the entrance to its home, has been discovered living in an unlikely place. Underwater.
It survives daily flooding of its home by creating a waterproof door over its burrow.
What Is the Mauritian Tidal Trapdoor Spider?
The Mauritian tidal trapdoor spider, scientifically named Idioctis marevallum, was discovered on tiny islands off Mauritius in 2023 and formally described as a species new to science in April 2026. Durrell Wildlife Conservation Trust, which was involved in the discovery, announced the finding on October 27.
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Researchers have described the spider as an "endemic species of intertidal trapdoor spider," which means it’s native to Mauritius and lives in areas regularly flooded by seawater.
It belongs to the Barychelidae family, which is a broad group of mygalomorph spiders that includes tarantulas. Mygalomorph spiders tend to have large, powerful fangs and thick, hairy bodies and legs. Think classic tarantula. But perhaps the most remarkable feature about this spider is how it copes with the ocean.
Researchers found that they nest in coastal areas that are either completely submerged by seawater or struck by waves every day. They survive by digging burrows and building trapdoors (hence the name) that stop seawater from flooding their homes.
Scientists from the Durrell Wildlife Conservation Trust initially thought that the spiders might be Tigidia mauriciana, another Mauritian trapdoor spider, which was discovered in the 19th century and has only ever been detected once, but examination of their anatomy eventually ruled that out.
Where Does the Mauritian Tidal Trapdoor Spider Live?
So far, researchers have only found the spider on Ilot Vacoas and Ile aux Fouquets, two islands in the Mauritian archipelago, the group of islands that make up Mauritius.
The species appears to have an extremely limited range, with researchers recording its presence across just 227 square meters of habitat on Ilot Vacoas and 686 square meters on Ile aux Fouquets.
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The spiders live in hard coralline rock in the intertidal zone, which is the part of the coastline that lies between the high-tide and low-tide marks. They like to nest on the southern sides of the islands where the waves are strongest. The researchers searched other seemingly suitable areas but didn’t find any additional nests.
Their homes are tube-shaped and about 12 centimeters, or 4.7 inches, long, lined with webbing and sandy material. The trapdoor is made from rock, sand and algae, which not only stops their residence from flooding, but also helps it blend into its surroundings.
Researchers tested the doors by pouring seawater over a nest for about 20 seconds and then opening it, finding that no water had accumulated inside. The spider also pulled down on the trapdoor while the water was being poured over it, potentially tightening the waterproof seal.
The species appears to be mostly active during the night, as they were seen extending their legs partly outside their burrows and wandering short distances away from them. Researchers also observed them capturing and injecting venom into prey near their trapdoors, and captive feeding observations showed them feasting on small crustaceans known as isopods, as well as crickets and moths.
What Does the Mauritian Tidal Trapdoor Spider Look Like?
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The scientific description is based on females, and the images published show a small, robust spider with a brownish body and sturdy legs, typical of mygalomorph spiders.
Camouflage extends beyond the spider itself. The entrance to its home can be difficult to distinguish from the surrounding coastal rock because its trapdoor is covered with natural material, as mentioned above.
When Was the Mauritian Tidal Trapdoor Spider Found?
The spider was first spotted in 2023 on Ilot Vacoas during conservation work under the Mauritius Island Restoration Programme, a partnership involving Durrell Wildlife Conservation Trust, the Mauritian Wildlife Foundation and the National Parks and Conservation Service, with support from the Forestry Service.
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Max Tercel, an entomologist who led the team which first identified the spider, spotted the species while searching coastal rocks with a headtorch after dark.
Recounting the shock discovery, he said: "It was dark by then, and I was carefully searching through crevices with my headtorch when, to my astonishment, I noticed a familiar pattern: a spider’s legs extending from its burrow, something I’d only ever seen before in lush forests and grasslands."
He added that he knew he’d found something special and called it a "privilege to be able to observe these wonderful creatures in their natural habitat."
Nik Cole, Durrell's Mauritius country manager and a member of the discovery team, said he initially "couldn’t believe something from the same group as tarantulas could be living in a place like this."
Newsweek has reached out to Max Tercel and Nick Cole for comment.
Newsweek’s reporters and editors used Martyn, our AI assistant, to produce this story. Learn more about Martyn here.
Contact Newsweek editors on this story: John Fitzpatrick and Tony Phillips.
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