Published in the Contra Costa Times on October 28, 2006

Q.  My garden is all of a sudden full of wasps. They tend to fly close to the ground and have stung me several times. I have looked under the eaves and in my trees but can’t find any nests.  How can I get rid of them?

A.  The wasps you are describing are called yellowjackets, and they are considered a species of social wasps. Not social as pertains to people, but social in that they live in large colonies. The ground nesting yellowjackets (Vespula spp) protect their nests very aggressively, and can be a real problem for gardeners. They tend to become more aggressive over time, as the colonies increase in size and food resources become scarcer.  Yellowjackets are different from paper wasps. The paper wasps build their nests up high, and are much less aggressive. Yellow jackets build their nests in the ground, often in abandoned rodent burrows, which they will excavate out if not large enough. The nests are truly beautiful, made of paper and resembling swirled clouds.  The wasps create the nests by mixing fibers scraped from wood with their saliva The nests begin in the spring with a single queen, who emerges in the late winter to early spring and begins to feed. She starts a new colony which quietly grows through the summer months, Worker bees collect protein to feed the larvae, often in form of dead insects, an attribute that people tend to approve of.  By late summer growth has slowed down, and large amounts of sugars are needed for feeding. You may have noticed large numbers of wasps on fallen fruit or clustered around hummingbird feeders. With the onset of cold weather the colony usually dies, although with mild winters the entire colony may overwinter, continuing to grow.  Colonies that began with a single queen can reach a population figure of over 15,000 wasps by the end of the summer.

Wasps can be described as beneficial when you consider the number of other pest insects they consume, and the debris collection they provide. The best way to avoid being stung is to avoid the wasps. Try and identify where the nests are located. If you sit quietly and watch, you may see where they are entering the ground. If you need control, use lure traps in the early spring so that large populations cannot become established. If a nest needs to be eliminated, call Mosquito-Vector control.  Using sprays to eliminate aggressive wasps is best done by professional and is very risky for homeowners. The wasps will attack as soon as they sense a poison being applied to the nest, even when sprayed at night. UC has a pest note on Bee and Wasp stings that describes some of the reactions that can occur, ranging from mild irritations to serious kidney damage.

Here are the URL’s for the UCIPM pestnote for more information, or call the Master Gardener desk at 925 646-6586

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7449.html

http://www.ipm.ucdavis.edu/PDF/PESTNOTES/pnyellowjackets.pdf