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Most species of yellowjackets, and all paper wasps, Polistes spp., 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.
Unless a nest is located in an area where it directly threatens people or pets, they should be left alone. But managing to keep a resident population away from human activities takes some care and thought.
Identify the insect correctly.
The paper wasps (about ¾ inch long) are longer than yellowjackets, 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. Paper wasps, in general, are less likely to provoke interaction with humans than are yellowjackets. They are generally docile unless the nest is disturbed. Vibrations and other disturbances can alarm them.
Yellowjackets are black and yellow, with a blocky shaped body about ½ inch long. The workers are the active ones that move around gardens and interrupt picnics. In August and September, the worker yellowjacket populations build up and 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.
Both yellowjackets and paper wasps die out completely in winter. For the purposes of this article, we'll concentrate on the yellowjackets. Only the queen overwinters, and she builds 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 yellowjacket queen starts a new nest and feeds young larvae for about 3 weeks, when they pupate to emerge as workers (infertile females.)
Once the yellowjacket workers appear, they tend and feed more larvae. Populations increase throughout the summer until they become quite noticeable this time of year. 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 yellowjackets 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 as structural pests such as termites or carpenter ants can.
Yellowjackets 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 yellowjackets moving in and out of an area, look for the nest. String trimmers particularly 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 and rock crevices and bits of tree bark, or 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 yellowjackets are in the area, avoid wearing perfume, heavy hairspray, or aftershave 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 flowered patterns.
If it is necessary to keep yellowjackets out of an area such as a picnic area, several different kinds of commercial traps are available. Most of them are constructed to hold a bait, such as sugar water or meat or fish. They are built so that once entering the trap, the insect can't emerge. Set traps away from picnic areas, at least ½ hour before putting out food. Ideally, the insects will be attracted away from your food to the trap. Keep garbage cans securely covered.
If the nest is close to a home, such as under an eave, removal may be necessary. A number of chemical products are registered for this. At night, when the yellowjackets are in the nest, preferably in the coolest part of the night, is the best time to work. Cover yourself including your head, face, neck and hands with thick clothing. Do not attempt to do this if allergic to the wasp venom. Get help from a professional exterminator if the nest must be removed and you are allergic. Sharon Collman, retired WSU entomologist, writes that some yellowjackets will aim venom at the eyes of a person who is even covered by a bee veil by squirting it through the veil. Yikes!
Further Reading:
WSU EB 0643 Yellowjackets and Paper Wasps
Hortsense: Managing plant problems with Integrated Pest Management
