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Reducing the Springtime Sting of Yellowjackets

Have you ever been stung by a yellowjacket? If you have, no doubt you remember it because unlike a bee that stings once, the yellowjacket can sting multiple times. Because yellowjackets can swarm and sting repeatedly, the Contra Costa Mosquito & Vector Control District offers a free service for yellowjackets in keeping with the District’s mission to protect public health.

In Contra Costa County, there are four types of yellowjackets – two that nest above ground and two that nest below ground. The Contra Costa Mosquito & Vector Control District’s free service is for the ground-nesting yellowjackets in particular.  “We only do ground nesting yellowjackets because they are more aggressive and in larger numbers, so they’ll swarm,” says Contra Costa Mosquito & Vector Control Supervisor Sheila Currier.

Ground-nesting yellowjackets most commonly appear as the weather warms in spring, building their nests in abandoned rodent holes, railroad ties or in soil cavities underground. The queen begins the building process, laying eggs through the spring and summer to produce the colony. The colony members then chew wood from fences or structures into a paper-like pulp in order to expand the nest. There can be as many as 5,000 yellowjackets in a single colony! The workers primary job is to protect the queen, build the nest and support the colony’s growth by foraging for food.

Yellowjackets do eat smaller pest insects, so they can provide natural insect reduction in many landscapes. Because they can also do incidental pollination through this process, yellowjackets can be viewed as beneficial to some extent. However, their principal source of food in the spring and early summer is meat to provide protein to the growing colony. That preference changes to fruit, soda and garbage in late summer as the colony’s dietary needs turn to sugar. That’s why these insects have gained a reputation for ruining countless picnics; because they are looking for the same things that are on the typical picnic menu.

Once yellowjackets make their presence known, the next step for homeowners is to identify the insects’ nest. One way is by spotting them as they enter or exit the nest in search of food. Yellowjackets typically exit the nest in the morning and return in the afternoon or evening. More often than not though, folks tend to find nests by accident – usually disturbing them while doing yard work.

Now that the nest has been located, marking it by placing a garden tool, hose or any clearly visible object at the location, then drawing a simple map describing the location is the last thing the homeowner must do before contacting the District for free yellowjacket service. To request service, contact the District at or dial 925-771-6184. A District employee typically responds to the call within one business day. A state-certified employee will then visit the location, verify the nest location and treat the nest with a plant-based powder insecticide that should be left alone for one day to make sure any yellowjackets that have exited the nest have had time to return and be exposed to the treatment. The powder is biodegradable. In the days following the treatment, yellowjackets will no longer inhabit the nest and the area can be returned to regular usage.

In cases where homeowners experience yellowjackets, but cannot find a nest, it is possible the insects are only foraging for food at the location and not setting up residence. These simple, natural steps can reduce the risk of yellowjackets.

  • Keep garbage cans covered with tight-fighting lids to prohibit the insects’ access to the garbage.
  • Pick up fallen fruit that will attract yellowjackets late in the summer.
  • Avoid swatting at or killing an annoying  yellowjacket. When threatened, yellowjackets release a hormonal chemical (pheromone) that attracts other yellowjackets to come to their aid. That is why more arrive on the scene once you swat at one.
  • About 15 minutes prior to a picnic or outdoor barbeque, place a plate with samples of everything on the menu in the furthest corner of the yard to attract the yellowjackets away from the picnic.  They will typically stay very loyal to the plate and leave the cook-out alone.

If someone in your family is allergic to yellowjackets or they present an overwhelming health risk, traps purchased from hardware or home improvement stores can be installed following the last hard freeze of winter. The trap should be located in the furthest location from the house because it will attract yellowjackets. It should also be checked regularly to maintain effectiveness.

The bottom line is yellowjackets are looking for the same thing we are – food and shelter. And while they can be beneficial in some situations, if they have taken up residence on your property, they can pose a potential health hazard. Simple steps can reduce the risk of yellowjackets on your property. For homeowners that find a nest on their property, contact the Contra Costa Mosquito & Vector Control District for free inspection and service.