Yellow Jackets Are Good In The Garden, But Not Near Food

After a cool, gray summer, it's enticing to spend evenings outside in the warm, late light. Dinner on the deck or a picnic on the patio seems just right in the weeks before and after Labor Day.

But picnics in August and September often attract that unwanted visitor, the German yellow jacket (a member of the wasp and bee family). These meat- and sweet-eaters will perch on a piece of fried chicken to compete with the human eater. They annoy people swigging from soft-drink cans and hover over summer fruit. They often try to fly off with a chunk of meat or fruit nearly their own weight. Canned pet food of all types also attracts these voracious insects.

There's a definite ecological niche for these insects. Most species of yellow jackets, and all paper wasps, Polistes sp., are basically beneficial predators in gardens. They kill countless insects and caterpillars. Late-summer nests of fall webworm provide them with lots of food. A friend who grows roses reported that his aphid problems had nearly vanished when a nest of paper wasps settled in his garden.

So unless a nest is located where it directly threatens people or pets, it should be left alone. But keeping a resident population away from human activities takes some care and thought.

First, identify the insect correctly.

Paper wasps, in general, are less likely to provoke interaction with humans than are yellow jackets; they are generally docile unless the nest is disturbed. Vibrations and other disturbances can alarm them. The paper wasps are longer than yellow jackets, about 3/4-inch long, with more slender bodies and legs that dangle when they fly. They are usually red and yellow or mostly yellow with some areas of black. Their nests are smaller, and contain open combs facing downward rather than being oval and enclosed. They generally fasten nests to building eaves.

Humans are much more likely to be bothered by the yellow jackets. Yellow jackets are black and yellow, with a blocky-shaped body about 1/2-inch long. They look as if they might provide inspiration for a graphic portrayal of a cartoon villain. The workers are the active ones that move around gardens and interrupt picnics. In August and September, the worker yellow jacket populations build up. They become more noticeable and can be downright maddening.

Their nests are large, paper ovals, often tucked into brush or shrubbery or down at the soil level in an opening like a mouse burrow. The nests are intricate, built of a wood fiber that completely encloses the nest except for a small opening at the bottom. The paper layers, striped in various brown tones, resemble artists' creations in fiber. One winter, I picked up an empty nest and took the layers apart to frame them for a wall hanging, because the fiber is so beautiful.

The wasps die out in winter. Only the queen overwinters, and she begins the nest anew each year. They don't reuse the nests, so it's safe to remove an empty nest in freezing weather after the populations have died. The yellow jacket queen starts a new nest and feeds young larvae for about three weeks, when they pupate to emerge as workers (infertile females).

Once the yellow jacket workers hatch, they tend and feed more larvae. Populations increase throughout the summer. The workers enlarge the original nest so that it often becomes quite large, bigger than a football, by the end of summer. You may observe yellow jackets pulling bits of wood off fences or house siding to chew up for nest material. This damage is generally superficial. They do not damage houses in the way that structural pests such as termites or carpenter ants can.

Yellow jackets defend their nests and their territory. Having once run into a nest with a hedge trimmer while pruning English laurel, I can testify to their vigorous efforts and the pain of their stings. Observe carefully before moving into hedges or thick shrubbery. If you see yellow jackets moving in and out of an area, look for the nest. String trimmers, in particular, cause vibration that can madden these insects.

Watch the way the insects are moving. When they are just foraging for food, they move slowly and search through plants, rock crevices and tree bark, also near water sources such as a leaky faucet or drippy sprinkler. If they are headed for the nest, they fly straight and it's often possible to locate nests by watching the flight pattern.

If yellow jackets are in the area, avoid wearing perfume, hair spray or after-shave when outdoors, because the scents attract them. A big bouquet of scented flowers on the picnic table might, also. They are attracted to yellow clothing, pink clothing, light blue and floral patterns.

If you must keep yellow jackets out of an area, several kinds of commercial traps are available. Most are constructed to hold a bait, such as sugar water, meat or fish. They are built so the insect can't emerge once it's entered the trap. Set traps away from picnic areas, at least one-half hour before putting out food. Also keep garbage cans securely covered.

If the nest is close to a door or window, or if allergies to insect stings are a problem, removal may be necessary. A number of chemical products are registered for this. The best time to work is in the coolest part of the night, when the yellow jackets are in the nest. Cover yourself, including your head, face, neck and hands, with thick clothing. Do not attempt this if allergic to wasp venom. Get help from an exterminator if the nest must be removed and you have any doubt about doing it.

Sharon Collman, retired Washington State University entomologist, writes that yellow jackets will even squirt venom through a veil, aiming at the eyes of a person who is covered by a bee veil. Yikes!

WSU Cooperative Extension has a comprehensive bulletin on these insects; call your local office and ask for EB 0643 "Yellow Jackets," which gives a number of options for control. There is a charge for the bulletin and for mailing it.

In King County, call 206-296-3900. In Snohomish County, call 425-357-6010. In Pierce County, call 253-798-7170.

The troublesome season for these insects is brief, but, alas, it coincides with a time when many of us want to enjoy the territory they occupy.

Gardening runs Sunday in Home/Real Estate. It is prepared by Mary Robson, area horticulture agent, Washington State University/King County Cooperative Extension.