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Yellowjackets

May contain: wasp, bee, andrena, hornet, invertebrate, insect, and animal
Yellowjackets have a shiny yellow and black body.

Yellowjackets are stinging insects that build large communal hives.

Three kinds of yellowjackets occur in San Mateo County: the Western Yellowjacket (Vespula pensylvanica), Common Yellowjacket (Vespula alascensis) and the Aerial Yellowjacket (Dolichovespula arenaria).

Western Yellowjackets and Common Yellowjackets build hives under the ground and feed on live insects, dead animals, and nectar. These are the insects that pester you during your summer and fall BBQs - they are sometimes called "meat bees."

Aerial yellowjackets build large paper nests in trees or other high places (such as the eaves of your house). These nests are round or oval shaped and about the size of a basketball. Aerial yellowjackets feed exclusively on live insects. 

 

May contain: wasp, invertebrate, bee, andrena, hornet, insect, and animal
A yellowjacket nest looks like a hole in the ground with yellowjackets flying or crawling in and out.

Most of the time, yellowjackets are not aggressive and will not harm you if you stay out of their way. The yellowjackets that you see flying about in the garden are simply collecting food for their young and are helpful in controlling harmful insects in your garden. However, when their nest is disturbed, yellowjackets will swarm out and attack the offender. If you find a yellowjacket nest, be careful not to disturb it. If it is in a place you are likely to come into contact with, you can call the District to remove the nest.

 

A computer-generated image of the side, underground view of a yellowjacket nest. The entrance to the tunnel is at ground level, in between blades of green grass. The tunnel goes down into the brown dirt until it forms a large round space. Inside the space is the nest, which is connected to the wall of the hole by being connected to a root. The inside of the nest has dozens/hundreds/thousands of little cells for the queen yellowjacket to lay eggs in. The cells are surrounded by a covering that protects the nest. The nest can be entered through a hole in the bottom of the nest.
Diagram of a ground-nesting yellowjacket nest. The small opening can lead to a very large nest.
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