PHONE
800-231-3236 (toll free)
707-285-2200 (office)
707-285-2210 (fax)
ADDRESS
595 Helman Lane
Cotati, California
94931-9736
HOURS
Monday through Friday
7:00AM to 3:30PM
Most service calls dealing with yellowjackets or wasps come in the late summer or fall, when colonies reach their highest numbers. In Marin and Sonoma counties, they usually involve one of five species: Vespula pensylvanica, V. vulgaris, V. germanica, Dolichovespula arenaria or D. maculata. The first two are by far the most common in the two county area, and the third has appeared recently from the eastern US.
Yellowjackets account for about half of all human insect stings. Unlike honeybees, their stinger is not barbed, and they can sting many times in succession. They can be especially aggressive in defense of the nest. Stinging and injured yellowjackets release a chemical alarm pheromone that attracts other guard workers.
Vespula yellowjackets usually make their nests underground, in abandoned gopher
or ground squirrel burrows, or other natural or artificial spaces. Occasionally they are
found in buildings, especially in the spaces inside walls. The nests are made from wood
fibers, chewed into a paper-like pulp. Dolichovespula yellowjackets make their
paper nests in bushes, branches of trees or other places in the open air.
Each colony is started in the spring by a single, fertilized female. She builds a small nest
about the size of a golf ball, containing 30 to 50 larvae that she feeds and cares for by
herself. Once the larvae emerge as infertile worker adults, they take charge of construction
and maintenance of the nest, while the original queen lays more eggs. By late summer the
colony can number 1,000 to 5,000 or more workers. The year's last generations are fertile
male and female wasps. The males and old workers soon die and the newly mated females fly
off to find safe places to wait until spring, when each starts a new colony of her own.
Adult yellowjackets feed mostly on items rich in carbohydrates, while the growing larvae need the protein-rich foods (insects, fish, bits of hamburger) brought back by the workers. The larvae in return secrete a sugar material eaten by the adults. In the late summer and fall, the larvae stop producing the sugar, and the hungry workers begin agressively searching out other sweet sources, like fruit, cake or soda.
You can find more on wasps in the District's public service bulletin: Yellowjackets in Residential Areas.
A helpful internet reference: Ohio State University Extension's FactSheet Yellowjacket Wasps.
To view and print the Districts Yellowjacket booklet (Adobe PDF): Yellowjackets of Marin & Sonoma.