A “scary” new spider species found beneath California’s beaches

Findings published in the journal Ecology and Evolution indicate that what long appeared to be a single species is actually two.

"While there are over 50,000 species of spiders worldwide, there are probably hundreds of thousands left to be discovered, even along the coast where new spider species may be hiding just underfoot of California beachgoers," said senior author Jason Bond, a professor in the UC Davis Department of Entomology and Nematology.

A hidden species revealed

Trapdoor spiders are small, secretive relatives of tarantulas. Females spend their entire lives in underground, silk-lined burrows that close with a hinged, well-camouflaged door. They wait motionless for surface vibrations, darting out only when prey strays within reach.

"There are now four known species of trapdoor spiders in California that live exclusively in coastal dune habitats," said corresponding author Emma Jochim, a doctoral student in the UC Davis Department of Entomology and Nematology. "The one we were looking at as part of this study was the most widespread, ranging from Moss Landing near Monterey down to Baja California -- which is a pretty wide range for a trapdoor spider, given that they don't easily leave their burrows to disperse."

To test whether look-alike spiders were masking more than one species, Jochim and colleagues examined genomic DNA from Aptostichus simus collected throughout its range. Bond had long suspected the presence of cryptic species, a term for species that appear similar but are genetically distinct.

The team considered both genetic evidence and where populations occur. Cryptic species are reproductively isolated.

"Based on what we know about their natural history and lifestyles, they're not going to be able to disperse to different coastal dunes to reproduce and 'mix' with each other," Jochim said.

What's in a name

Professor Jason Bond decided to name the new brown, chunky, quarter-sized spider Aptostichus ramirezae. Bond is no stranger to naming new spider species. The arachnologist has named species after celebrities, musicians, photographers and even magicians. Notables include Aptostichus stephencolberti or Myrmekiaphila neilyoungi and Aptostichus barackobamai.

This new species is named for Martina Giselle Ramirez, dean of the College of Science at California State University, Stanislaus and formerly dean of natural sciences and biology professor at St. Norbert College. Ramirez is a highly regarded arachnologist who pioneered early works on trapdoor spider population genetics and has championed underrepresented students in STEM disciplines.

More than a Halloween creature

The scariest part about this discovery isn't the spider, it's what could happen if its home is lost for good.

Both Aptostichus simus and Aptostichus ramirezae live only in coastal dunes from central California to northern Baja California, Mexico including some in the Channel Islands. These habitats are shrinking due to many factors including development, erosion, wildfire and sea-level rise.

"They're definitely at risk, especially the lineage Aptostichus simus," Jochim said. "The new species has a much wider range, but Aptostichus simus is now really only found in San Diego, and projections for sea-level rise in that area are very grim. These spiders are not really able to adapt that quickly to new habitats."

Clarifying the genetic differences among populations helps identify which groups most urgently need protection. Although spiders can seem spooky to study, Jochim noted that documenting them deepens our understanding of Earth's biodiversity.

"If we don't know how many species are in an area or understand the patterns of genetic diversity between populations, we don't really know what areas would be most important for conservation efforts," she said.

Other contributors to the study are James Starrett and Hanna R. Briggs of UC Davis. The work received support from the National Science Foundation.