Contra Costa Sees Rise in Yellow Jacket Nests This Season

For the past 25 years a foreign wasp has been extending its invasion of Northern California from a beachhead in Sacramento. Summer after summer, sting by sting, the European paper wasp is working its way down the Delta to the Bay Area.

Nearly identical to the Western yellow jacket, the encroaching insect may be responsible for a spike in complaints about its native cousin, according to an article in Sunday’s San Francisco Chronicle. This is the time of year when yellow jacket nests are at their highest densities and the venomous bugs shift their diet from plump, protein-rich caterpillars to sugars and carbohydrates. They want to sip that can of soda at your picnic or barbecue.

So far this year, the Contra Costa County Mosquito and Vector Control District has fielded 441 yellow jacket reports compared to 416 at this time last year. The jump in complaints may also be due to yellow jacket ingenuity. According to Deborah Bass, the district’s public affairs manager, yellow jackets are exhibiting unusual nest-building techniques this season.

“We find that there is a much longer entryway to get to the heart of the nest. Therefore, when we use our insecticide, it doesn't always reach the yellow jackets. The queen then reestablishes a nest right next door, sometimes mere inches from the old nest. Because the first treatment doesn't kill the yellow jackets, a second or third treatment is required,” Bass wrote in an email.

In a quote that will send shivers down the spine of any entomophobe, Vernard Lewis, an insect scientist at UC Berkeley, told the Chron that “something is up” with the bugs. 

“It's not just yellow jackets,” Lewis said. “It's other pests, too, like cockroaches. It's the most I've seen in at least 10 or 15 years."

Do you have a yellow jacket nest on your property that you'd like removed? Request a visit from county technician here.