Are all yellowjackets the same? The short answer is no. All yellowjackets are not the same. Here in Contra Costa County, there are four types of yellowjackets: two that build above-ground nests and two that build underground nests. 

The Contra Costa Mosquito and Vector Control District's (District) service is specifically for ground-nesting yellowjackets because they are more likely to bother people. Yellowjackets that build aerial nests feed mostly on other insects and don’t usually cause problems unless their nest is intentionally disturbed.

This time of year, in the late summer and early fall, yellowjackets are attracted to sweet foods and drinks, such as candy, fruit, and soft drinks. 

The Western yellowjacket (Vespula pensylvanica) is a common ground-nesting yellowjacket species in Contra Costa County. They can be observed entering and exiting a hole in the ground. 

Yellowjackets live in colonies, which can contain hundreds of yellowjackets. Ground-nesting yellowjackets build their nests in abandoned rodent burrows and other holes or voids in the ground.

Folks often find a yellowjacket nest in their front or backyard by accident, usually while gardening or mowing the lawn. If a resident finds a ground-nesting yellowjacket nest, the most important thing to do is to drop the tool or stop the lawn mower right then and there and avoid the area. Yellowjackets can bite and sting, and when their nest is disturbed, they can be aggressive when defending the colony.

If a resident finds yellowjackets going into the same area (a hole in the ground or under a shrub), that may be evidence of a nest on the property. If the property is within Contra Costa County, the resident can contact the District for ground-nesting yellowjacket service.

While performing the District's service, if the resident leaves a tool or item near the possible nest location, that can help the District technician find the area more easily. Another way to help the District technician find the nest is by drawing a simple map of the yard showing where the potential nest is located and leaving that map taped to the front door or side gate.

Once the technician finds the nest, if the technician confirms ground-nesting yellowjackets are present, the technician will treat the nest with a public health pesticide that is an insecticidal dust. After the nest is treated, the resident should leave the nest alone for at least four days while making sure the area remains dry.

It's important to note that the District only treats dry ground nests. If someone working in the yard has recently tried to treat the suspected nest with a liquid or any other substance, the resident must wait a few days before contacting the District for the District's Groundnesting-Yellowjacket Service because wet soil will interfere with the District's treatment.

Another way to control yellowjackets in a yard is by using yellowjacket traps that are most effective if installed during specific times of the year and when using the appropriate bait to catch the yellowjackets.  Yellowjacket traps should be installed away from walkways and places where people reside, preferably on a back fence or other area away from the house. 

In Contra Costa County, early in the year, when the yellowjacket queens are emerging from a type of hibernation, put up yellowjacket traps on Valentine's Day and take them down on Father's Day, in order to intercept newly emerged queens and prevent them from starting new colonies. It’s best to use the attractant bait included with the trap. 

Later in the year, if yellowjacket activity continues into late summer and early fall, Contra Costa County residents can put traps back up. When putting a trap up again, follow the same recommendations to keep it away from areas where people may be and away from the house. During late summer and early fall, the attractant should be sugar-based, like fruit juice, sugar water, or jam, that can attract worker yellowjackets that might be foraging in the yard.  

To receive ground-nesting yellowjacket service, Contra Costa County residents can request the District's service by phone at 925-685-9301 or online.