Previously, these spiders — brown, cute and around the size of a quarter — were thought to be Aptostichus simus, a close relative and lookalike. Researchers suspected they might be distinct, so they analyzed genetic material to distinguish between the two species.
“We knew that these lineages across the coast of California were really different from each other and had been separated for a very long time,” said Jochim, a researcher in the Department of Entomology and Nematology at UC Davis.
Emma Jochim does field work in the dunes at Stinson Beach (Courtesy of Emma Jochim/UC Davis)
The species share similar life histories and ecological roles — preying on arthropods like beetles in coastal dunes — but they don’t interbreed, partly because they rarely move far from their burrows.
“The females never leave their burrows, only the males do,” Jochim said.
Partially because moving from one beach to another would be almost impossibly hard.
“Especially because there’s a lot of rocky coastline in between the different populations,” Jochim said. The spiders can’t live on the rocks, only in sandy dunes.
To locate them, she looks for slopes covered in native plants. The spiders don’t care for European beachgrass or iceplant, originally from South Africa.
“We start digging at the bottom of the hill and as the sand falls down, the burrow — if it’s present — will kind of flop over,” Jochim said. “It looks like a sand-covered sock.”
These elusive spiders are related to tarantulas, which also make burrows. But trapdoor spiders take the engineering a step further, camouflaging the entrances to their burrows.
The hinge of the door, Jochim explained, is made of silk. The door helps regulate temperature and humidity in the burrow.
“It works opposite of what you would imagine a trap door to do,” she said. “Prey doesn’t fall into the burrow from the door, but the spider lunges out from it to capture prey and then goes back in the burrow.”