New Spider Species Remind Us Just How Much We Don't Know About the Desert

Trapdoor spider from the California desert | Photo: Marshall Hedin/Flickr/Creative Commons License

If you're one of the millions of people who fear spiders, it might be a bit unsettling to realize that California is full of them -- the desert especially so. From our striking tarantulas with their three-inch leg-spans that wander desert roads in September to the near-ubiquitous black widows hiding under debris, the deserts of California host an astonishing number of spiders -- one or more per square yard in many spots. It's no surprise that of 33 recently-discovered species of trapdoor spiders living in western North America, many -- including one named for U2's frontman Bono -- make their living in the California desert. But their discovery does serve to remind us that our deserts are largely unexplored by biologists, and that we may be losing species before we know they're there.

In a paper published in December in the journal Zookeys, arachnologist Jason E. Bond of Auburn University describes 33 new species of the trapdoor spider genus Aptostichus, most of which live in California. The California desert is well-represented in the new species' habitats, with 13 of the new species discovered here, ranging in location from Aptostichus derhamgiuliani, named for the late desert biologist Derham Giuliani, in the Eureka Valley in Inyo County, to A. hedinorum, which inhabits the southern reaches of Anza Borrego Desert State Park.

The majority of the remainder live throughout the rest of California from the North Coast to San Diego, with a few in Arizona and Nevada.

Bond has received some press for his lighthearted approach to naming spider species. One species discovered in the Covington Flat area of Joshua Tree National Park received the name Aptostichus bonoi, after the Irish musician most associated in the public mind with Joshua Tree (though U2's iconic photos actually depict a now-fallen tree in Death Valley National Park.) An Arizonan species bears the name A. edwardabbeyi after the desert writer, and two species found in the San Joaquin Valley now boast the monickers A. dorothealangeae and A. chavezi, after the photographer and the United Farm Workers' leader respectively. Bond bestowed a most formidable name on species found in the rolling hills north of Red Bluff: Aptostichus barackobamai.

Bond's proclivity for paying tribute to celebrity in his naming is not a new trait, as it happens, as you can see from this 2008 clip of what's very likely the most prominent discussion of spider taxonomy in world history.

Trapdoor spiders are hard to spot, even when you're looking for them. As you might guess from their name, they excavate burrows which they cover with trap doors, generally flimsy and translucent masses of spider silk and plant debris attached by a silken hinge. Trapdoor spiders are ambush hunters. They lay in wait in their burrows until a likely meal ambles past, then burst out into the open to capture it. Many trapdoor spider species use triplines to sense when a potential prey animal is near. Aptostichus belong to the group informally called "wafer trapdoor spiders", as they build trapdoors that are thin and somewhat gauzy compared to so-called "true trapdoor spiders," whose doors are thicker, almost plugging the holes to their burrows like corks.

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Male Aptostichus are somewhat more likely to venture out into the open than females, and can occasionally be caught in pitfall traps -- plastic buckets set into holes in the ground so that their rims are flush with the soil surface, then checked in the morning for animals.

Otherwise, finding trapdoor spiders -- especially females -- is a laborious process. In habitats with a fair bit of plant debris, biologists might have trouble finding the spiders' burrows, so deftly are they built to blend in with the surroundings. According to Bond, the burrows can only be spotted by scraping a centimeter or so of leaf litter off the ground to reveal the holes that the spiders call home. In sandy desert lands, finding the burrows is even more difficult, and biologists must wait until winter rains. After a rain, the spiders will clean out their burrows, leaving telltale mounds of sand and soil at the entrances. At that point, a diligent biologist might be able to collect the busy spider for identification.

In other words, it's hard to find the spiders even in the best of circumstances. To make things worse, females of different Aptostichus species are so similar it can be hard to tell them apart even for an expert. (In his paper, Bond quotes one expert as calling the task of separating females by species "hopeless.") So it's not too surprising that our knowledge of Aptostichus spiders isn't as deep as it might be. The genus was first named in the 1908, but despite abundant collections over the intervening century it's only been in the last decade or so that serious attention has been paid to Aptostichus by taxonomists like Bond.

And as you might expect, we seem to be losing these spiders even as we discover them. Trapdoor spiders don't migrate far, and many species seem to be restricted to relatively small areas. Of the 33 new species Bond describes in the Zookeys paper, two seem to be extinct -- including Aptostichus lucerne, native to the sprawling Apple Valley area, a close relative of A. bonoi. Three quarters of all known Aptostichus species are threatened with extinction.

It's a sobering reminder: so much of what lives in the desert is unknown to us, and we run the risk of losing it if we develop the desert for our suburbs or our industry. We stand to learn so much about what the living desert holds. Sometimes we need only scrape the surface.

Chris Clarke is an environmental writer of two decades standing. He writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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