California Is Finally Enjoying Some Rainfall—and So Are Its Invasive Species

After yet another huge winter storm blew through northern California in March, Rafael Rodriguez headed out to Steelhead Creek, just outside Sacramento, to measure its flow. An environmental consultant for the regional flood control agency, he wasn’t surprised to find the muddy torrent two feet higher than normal. Strong El Niño storms have drenched the drought-plagued state, particularly in the north. But as Rodriguez hiked out, something strange caught his eye: a red and gold snake, five feet long, suspended in branches overhanging the creek.

“It was the first time I’d ever seen a snake in that channel,” he says. “I didn’t recognize it.”

Rodriguez snapped a photo, which quickly made its way to the Invasive Species Program of the California Department of Fish and Wildlife, where it caused quite a stir. “There’s been a flurry of e-mails,” says Martha Volkoff, a member of the program. That’s because the serpent is a northern water snake, Nerodia sipedon, an invasive species never before seen in the area. The reptile was more than 12 miles from the only known location of the slitherers in the state.

First documented in California in 2007, Nerodia are native to the eastern United States. They may make for intriguing pets, but when threatened the snakes strike repeatedly and release a nasty-smelling musk mixed with poop. Wonderful traits like those, officials assume, may have led to their abandonment in the wild, where they prey on native amphibians and fish, including juvenile salmon, and compete with the giant garter snake, a threatened species. California’s five-year drought was actually helping the state’s efforts to eradicate the snakes, which began last year. “It shrank their habitat, which increased our chances of getting them all,” Volkoff says. “Now it looks like they haven’t been contained to that area. We don’t know whether the snake traveled on the high flows, but the timing was spot-on.”

Despite the increased precipitation, there is no end in sight for the drought. The statewide snowpack average is currently at 87 percent of normal—a significant improvement from last year’s scary-low 5 percent, but nowhere near the 150 percent level that water officials say would be needed by tomorrow to declare the drought over.

Nerodia snakes are just one invasive species that might be getting a boost from El Niño, even as the system fades. “It is likely a lot of weeds that are in the deserts and foothills will have an explosive spring as the water activates the large seed banks,” says entomologist Mark Hoddle, head of the Center for Invasive Species Research at the University of California, Riverside. He expects to see the effects of the rains extend through the spring and beyond. One species of particular concern is Sahara mustard, a rapid-growing invader that can choke out native plants.

Exotic plants might also gain footholds in mudslide scars, given their ability to recolonize more quickly than natives. Yellow starthistle, for instance, moves in, creates dense formations, and sucks up soil moisture, making it difficult, if not impossible, for native plants to take root. The weed, introduced to the state in 1850, now covers an estimated 10 to 15 million acres.

And then there are the skeeters. Pools of standing water from rains and snowmelt make ideal breeding grounds for mosquitoes—both non-native Aedes, which can transmit Zika, dengue, and other exotic diseases, and native Culex mosquitoes, which carry the invasive West Nile Virus.

Wildlife officials are tracking the invaders’ spread, but CDFW’s Volkoff says the public can do several things to help, including not planting pests and reporting any invasives they see. And for those boaters out there looking forward to enjoying full lakes and rushing rivers this year, make sure no quagga or zebra mussels have hitched a ride on your craft. We westerners welcome the water but need to be careful about what it washes in.

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