Citizen Spider Science: Tracking the Decline of L.A.'s Black Widows

Another story in our series on citizen science in California, as part of Redefine's celebration of Citizen Science Day on April 16.

As a child running around summer camp in the hills of Simi Valley I learned how to identify – and keep away from – black widows. The trick was to spot the red hourglass-shaped mark on its underside. While a black widow bite isn't usually fatal for people, the spider's neurotoxin packs quite a punch: pain, muscle rigidity, vomiting, and sweating for a start. Better to keep a distance.

Nowadays, kids are less likely to run into a black widow, though that hourglass is still a good indication of danger. That's because black widows in the LA area have largely been replaced by their cousins, the brown widows, who also bear a characteristic reddish hourglass. And a citizen science project started by the Los Angeles County Natural History Museum has helped document the change.

The story of brown widows in Los Angeles begins in 2002. According to Brian Brown, entomology curator at the Natural History Museum of Los Angeles, that's when the museum began encouraging Angelenos to capture spiders from their houses and backyards and bring them to the museum. Since the Spider Survey citizen science program started, more than 1,000 families have contributed more than 5,000 eight-legged specimens to the museum's collections. "They brought them in every conceivable container you can imagine," says Brown, including one empty bottle of Chanel No. 5.

But Brown isn't a spider expert; his passion is tiny flies. The job of identifying every specimen falls instead to museum volunteer Jan Kempf.

As a child, Kempf was already intrigued by the natural world. She was the sort of kid who chased after lizards in the backyard. That might explain why she began docent training at the museum twenty-six years ago. At the end of the training year, participants had to present a research paper. "I decided to research something I didn't know anything about, and it ended up being spiders," she says. She was hooked. She began taking classes in her spare time on spider biology and spider identification. Before long she met Brown, and she quickly transferred from the docent program to volunteering in the entomology department.

Her interests, plus those of a postdoctoral scholar working at the museum in the early 2000s, led to the initiation of the spider survey. "There hadn't ever been a comprehensive urban spider survey in Los Angeles," she said.

The spider survey is different from some of the museum's more recent smartphone-focused efforts, like RASCals or the Squirrel Survey. It's impossible to identify an individual spider to the species level without a good close look at its genitals, which means that actual physical specimens are required. Now that the postdoc has long moved on, Kempf is the museum's resident self-taught spider expert. Having retired, she's got lots of time for peering at the spiders' reproductive apparatuses under a microscope.

Some spiders, though, are more quickly identifiable. In the survey's first year, a museum educator was at a school in Torrance helping students look for spiders. One of the kids approached the educator holding a leaf with a spider on it and asked what it was. "Oh my god, that's a widow," she said. "And it's a weird one."

Unlike our native black widows, their brown cousins hail from Africa. Researchers knew that the brown widow had made its way to other spots in the world, including in California, but that specimen was the first evidence that the species had arrived in the Los Angeles area.

The museum's spider team, including Kempf and Brown, returned to the school to see if they could find any more. "The place was just rife with them, just chock-a-block with brown widows," says Brown. He recalls finding some underneath the benches where the kids ate their lunch. Kempf recalls finding them hanging from the chain-link fences surrounding the schoolyard.

A bite from a brown widow does deliver a neurotoxin, same as the black widow, but they're not really all that aggressive. Brown widows, says Brown, "are really shy and retiring spiders." Still, once the news broke, parents became concerned. But when a non-native spider decides to make a home in a new place, there's often little that can be done.

Indeed, says Brown, "for a couple years they were localized down in Torrance and Fullerton, and then all of the sudden, they just went FOOM!" Brown pantomimes a mushroom cloud exploding with his hands. Something changed that suddenly the species managed to colonize the entire L.A. Basin, almost completely displacing their native cousins.

"That's what happens with a lot of invasive species," says Brown. "They get established and they're present in low numbers, and then something changes either in the genetics of those organisms or in the local environment that allows them to escape."

In the case of the brown widows, their movement strategies help. After the young spiderlings hatch out of their spiky egg cases, they set out in search of new territory through a process called ballooning. They release a bit of silk, and like a kite, it gets caught up in the wind. Since the newly hatched arachnids are so light, they can easily ride their makeshift kite until they settle down somewhere else.

Today, "there are brown widows underneath every piece of lawn furniture in LA County," Brown says. "I'm sure of it." Since Brown easily won the last entomological bet he placed, it's probably not worth challenging him on the matter.

But he'll probably be able to prove it regardless. While the museum still accepts spider donations from any citizen scientist, the focus of the spider survey has shifted to the new Super+ Project. In addition to a Malaise trap, which collects flying insects, the citizen scientists participating in this project whose homes range from the coast to the desert, also have a cover board in their yards. These are simple pieces of plywood that lure small critters with the promise of protection, shade, and shelter. Every couple weeks, participants lift up the cover board to see what spiders might be lurking beneath.

If Brown is right, and I'm betting he is, he'll find plenty of brown widows.