A new species of trapdoor spider has been formally described after conservationists unexpectedly discovered it hiding in a hole on Ilot Vacoas – a one-hectare island off the south-east coast of Mauritius.
The Mauritian tidal trapdoor spider (Idioctis marevallum) lives in the island’s intertidal zone in tubes in the coralline (algae) bedrock, which are thought to have been created by molluscs and worms thousands of years ago. It seals the entrance to the tube with a trapdoor made from silk, sand and algae, protecting itself against high tides and waves.
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It was first spotted on the island of Ilot Vacoas in 2023 during conservation work that was being carried out as part of the Mauritius Island Restoration Programme. The programme is a partnership between Durrell Wildlife Conservation Trust, the Mauritian Wildlife Foundation and the National Parks and Conservation Service, with additional support from the country’s Forestry Service.
“Finding these trapdoor spiders was amazing, it felt like uncovering a hidden treasure,” says Max Tercel, an entomologist who led the team that found the spider. But the new species could’ve easily been missed.
“Earlier that day, I had been surveying other habitats on the island, and all that remained was a stretch of coastal rock with sparse vegetation – not somewhere we expected to find something so remarkable.
“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. I was completely stunned.”
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The spider has now been formally described in a study of Mauritius’s spider fauna by an international team of researchers. The discovery, published in the journal Arachnology, has increased the known spider diversity of the island nation by more than 25 per cent – although Idioctis marevallum remains an exciting find.
“The thing I remember most is Max screaming at me to come over because he’d just seen a mygalomorph – a trapdoor spider,” recalls Nik Cole, who was part of the conservation team and is the Mauritius country manager at Durrell Wildlife Conservation Trust.
“I couldn’t believe something from the same group as tarantulas could be living in a place like this. I was up all night, holding my phone in the air trying to get a signal and searching for any evidence of a spider like this in Mauritius. At first, we thought we might have found Tigidia mauriciana, which was first described in 1892 and had only ever been detected once.
“To discover this was actually a new species, after decades of nighttime reptile surveys on these islands, was incredibly exciting.” Following the initial discovery of Idioctis marevallum on Ilot Vacoas, the species has also been found on Ile aux Fouquets – another small island off south-east Mauritius.
Read the full paper here.
Top image: a Mauritian tidal trapdoor spider on the coralline bedrock. Credit: Durrell Wildlife Conservation Trust
