By 9 o’clock on a frosty morning, crows were already rototilling a baseball field in Seattle’s Delridge neighborhood. Prowling in groups of three and four, the glossy birds yanked up clumps of grass and poked through the exposed clods. Gulls circled overhead but didn’t land — yet.
Just give it time, said Dewright Brooks. A virtual aviary converges on the green expanse of Riverview Playfield every day — sometimes in the hundreds — as evidenced by wide swaths of uprooted sod.
“This is one of the worst fields in the area,” said Brooks, of Seattle Parks and Recreation’s turf crew.
“Worst” is a subjective term, of course. For the crows and their fellow foragers, it doesn’t get much better than this — short of a dumpster filled with hamburgers and french fries.
Brooks and his colleague Patti Bakker had only to turn over a few shovelfuls of dirt to reveal the reason behind the Hitchcockian assault on the lawn: C-shaped grubs less than an inch long, pearly white and irresistible to wildlife.
“It’s a great source of protein,” said Bakker, manager of wildlife and integrated pest management.
The grubs are the larvae of the European chafer, a nonnative scarab beetle first spotted in Washington state in 2008. By 2016, the chafer had taken up permanent residence near Seattle-Tacoma International Airport.
“It’s just been exploding since we first found it,” said Todd Murray, director of Washington State University’s Puyallup Research and Extension Center.
The beetles’ initial proximity to the airport suggests they may have hitchhiked on cargo planes, but multiple routes are possible including overland shipments of agricultural products. They’ve now spread as far south as Puyallup and as far north as Kirkland and aren’t about to stop, Murray said.
Though not as fearsome as the murder hornet, the European chafer joins an ever-expanding list of invasive species causing ecological headaches. While the hornets have the potential to wipe out bees, Murray fears the European chafer could pose the biggest threat in nearly half a century to turf grass lawns and athletic fields in the Pacific Northwest.
“It could be pretty devastating,” he said.
The larvae damage grass by feeding on the roots. But it’s the crows and other creatures — including raccoons and skunks — that have caught people’s attention this season as the animals strip-mine yards and medians and parks in pursuit of tasty snacks.
Neighborhood blogs and Nextdoor hubs lit up with conversations about what’s going on and what to do about it. One poster in West Seattle said she replaced her lawn with bark after repeated infestations. Another was optimistic his grass was resprouting after being plucked nearly bare.
It’s not surprising crows were apparently the first to catch on to the new food source, said University of Washington biologist John Marzluff, who studies interactions between birds and humans. Other types of grubs are already part of their diet, and the intelligent birds spend a lot of time probing the environment around them.
Once one group of crows finds something new, other birds watch and learn. “I could see it spreading pretty quickly once they are onto it because of their social nature,” Marzluff said.
In British Columbia, where the beetles gained their first West Coast toehold in the early 2000s, even black bears sometimes take advantage of the banquet.
Wildlife can provide at least a limited check on European chafer populations, Bakker said. But given the amount of damage caused by their excavations, letting nature take its course won’t be acceptable in some places, like municipal fields used for a wide range of sports and recreation.
In their current state, the baseball diamonds at Riverview Playfield would be hazardous, Brooks said, pointing out churned-up patches throughout the infield. “You could get some real ankle-breakers.”
So far, the heaviest Seattle-area concentrations of Amphimallon majale — the chafer’s scientific name — are in the South End, including Rainier Valley, South Park and West Seattle. SeaTac, Burien, Renton and surrounding communities also have thriving populations.
As the beetles spread, more homeowners are likely to face decisions about whether to maintain their grass lawns or look for alternatives, Murray said.
The short-lived adult beetles, which swarm from the ground in June and July, prefer to lay their eggs in sparse, dry grass. So lawns that are marginal to begin with are the most likely to suffer.
Seattle’s Parks Department is trying to figure out the most ecologically benign way to keep its fields healthy. Murray and his colleagues are researching recommendations for homeowners. Among the options are parasitic worms called nematodes and Bacillus thuringiensis, a type of soil bacteria toxic to some larvae.
Alec Kowalewski, a turf expert at Oregon State University, plans to collaborate with Murray on a survey this summer using ultraviolet light traps to lure adults and get a better idea of how widespread the beetles have become.
Since female beetles don’t like to lay their eggs in wet soil, one of the simplest control measures may be more regular watering in the summer, Kowalewski said.
Lawns already have a reputation as water hogs, so pouring on more isn’t ideal. But governments, in particular, need to consider the economic trade-offs, he said.
“If you are comfortable putting your tax money toward fixing public parks destroyed by the insects, that’s an option,” Kowalewski said. Another is surveying for the grubs and taking action — which could include extra water and judicious use of pesticides — when levels reach a threshold of destructiveness.
The worst thing would be to indiscriminately douse lawns and fields with bug-killing chemicals, Murray said. That’s what happened during the last big lawn pest invasion in the 1970s and 1980s. Back then, the culprit was the European crane fly. People across the Northwest fought back with highly toxic pesticides that wound up running off into drains and poisoning birds.
Today’s insecticides may not be as ecologically disastrous, but some can kill beneficial species, like bees. The city of Seattle doesn’t allow pesticides on its play areas or athletic fields, Bakker said.
Most invasive insects enjoy a boom period when they move into new areas, Murray pointed out. But eventually, ecosystems adjust and natural predators and other factors combine to impose a type of equilibrium.
“I suspect the European chafer will at some point be only a sporadic pest,” he said. “But it’s going to take a number of years for that kind of natural control to happen.”
For those who like crows, there might be at least one short-term benefit, Marzluff said. If parent birds have a reliable source of nutritious grubs to feed their offspring, more of the chicks might survive.