Contra Costa Mosquito & Vector: Act Now to Reduce the Risk of Yellowjackets

Press Release

Photo by Contra Costa Mosquito & Vector Control District

The following information was released by the Contra Costa Mosquito & Vector Control District who has already received 11 requests for ground-nesting yellowjacket services.


They live right under our feet and when we least expect it, they bite and sting repeatedly. It’s only February 2020, but they are already back.
So far this year, the Contra Costa Mosquito & Vector Control District has received 11 requests for ground-nesting yellowjacket service. That is more than any of the five previous years, including 2019, and 2019 was a big year for ground-nesting yellowjackets.
Over the last five years, the number of requests the District has received for ground-nesting yellowjacket service has increased steadily, with a record-breaking number of requests in 2019. Does that mean we are in for another record-breaking year this year?
According to Sheila Currier, the District supervisor who oversees the District’s ground-nesting yellowjacket program, “Yellowjackets will hunker down over winter and wait for warmer weather before they come out to look for new nest locations. A very cold winter can help reduce the population; however, this winter has been fairly mild. So far, it appears as if the ground-nesting yellowjackets are getting an early start, but it’s too soon to tell if this momentum will continue all year long.”
What can Contra Costa County residents do to reduce the risk of these biting and stinging insects now that they are already on the move? The short answer is–trap them now.
Set Out Traps Now in an Effort To Catch the Queens 
By putting out reusable yellowjacket traps now, even as early as Valentine’s Day, you have the best chance to catch the queens before they have a chance to start building a new colony.
  • Purchase new reusable traps from a home or garden store, or get out last year’s reusable traps.
  • Hang the traps away from where people and pets like to be. The best locations are high in trees at the edge of your property.
  • Use fruit juice in the traps for the next couple of weeks because the queens can be attracted to the juice.
  • Around St. Patrick’s Day, start using the pheromone insert that is usually sold alongside the reusable traps in home and garden stores. The insert will attract worker yellowjackets to the trap by mimicking their own hormones.
When to Call the District 
The Contra Costa Mosquito & Vector Control District  provides inspection and treatment of ground-nesting yellowjacket nests only. If you are seeing yellowjackets coming out of a hole in the ground on your property, or out from under a bush or other ground-level vegetation, please mark the nest by placing a tool or other marker as close to the nest as you can safely. Also, draw a simple map of your yard pointing out the location of the nest, and tape the map to your front door or gate. Then call the District at 925-685-9301 or visit the District’s website to request ground-nesting yellowjacket service.
Once you’ve requested the District’s ground-nesting yellowjacket service, be sure to leave the nest alone. The nest must be dry and untreated when the District technician arrives to inspect the nest. The District does not make appointments. A technician will arrive to provide service usually within five business days.