Follow-up reporting on the Mauritian tidal trapdoor spider, *Idioctis marevallum*, adds striking new detail about how the animal survives daily submersion.

The spider builds a tube-shaped burrow about 12 centimeters (4.7 inches) long, lined with webbing and sandy material, capped by a trapdoor made from rock, sand and algae. When researchers poured seawater over a nest for roughly 20 seconds and then opened it, no water had accumulated inside.

Entomologist Maximillian Tercel told Newsweek that the waterproofing comes from two factors working together: the door's construction material and the fact that the spiders actively hold the door shut when submerged, potentially tightening the seal.

The species is a member of the Barychelidae family, a mygalomorph group that includes tarantulas — animals with large fangs and thick, hairy bodies. Living in the intertidal zone is exceptionally unusual for such a lineage.

Tercel told Newsweek that the overwhelming majority of spiders, let alone trapdoor spiders, live in soil or vegetation well away from the sea, and that this example is only one of a very few worldwide where a spider lives in a zone submerged daily.

The spiders nest in hard coralline rock on the southern sides of the islands, where the waves are strongest — a preference Durrell's Mauritius country manager Nik Cole said he initially couldn't believe, questioning that something from the same group as tarantulas could live in such a place.

The newly reported habitat figures underline how precarious this species' hold may be. Researchers have found the spider only on Ilot Vacoas and Ile aux Fouquets in the Mauritian archipelago, occupying just 227 square meters of habitat on the former and 686 square meters on the latter.

The species was first spotted in 2023 during the Mauritius Island Restoration Programme, a partnership involving Durrell Wildlife Conservation Trust, the Mauritian Wildlife Foundation and the National Parks and Conservation Service.

It was formally described as a new species in April 2026, after anatomical examination ruled out an initial guess that it was *Tigidia mauriciana*, a Mauritian trapdoor spider known since the 19th century.

Tercel recounted the moment of discovery to Newsweek: searching coastal rock crevices after dark on Ilot Vacoas, he was astonished to see spider legs extending from a burrow, something he had previously seen only in lush forests and grasslands, and he called observing the creatures a privilege.

Surveys of Round Island and Gunnar's Quoin found no spiders, and while Tercel said the species could still occur elsewhere around Mauritius, he considers that unlikely based on searches so far.

The spiders are mostly active at night, ambushing prey near their trapdoors; captive feeding observations showed them eating isopods, crickets and moths. That extreme restriction to two tiny islets makes the species a striking candidate for conservation attention.