I have been getting calls regarding stings from hornets and yellowjackets. This is a good reminder that it is time to give some information on controlling nests of wasps and hornets. Yellowjackets, baldfaced hornets and paper wasps are coming out of nests which are hidden in cracks in the foundation, behind loose bricks, from nests hanging on shrubbery or buildings, and from holes in the ground. Changes in the insects’ dietary habits this time of the year bring them near human food, and the danger of being stung increases. Wasps are predators that feed off of insects including caterpillars, flies, crickets, and many other pests and their young. During late summer and fall, the queens stop laying eggs and their nests decline. At this time the wasps change their food to sweets and other carbohydrates, and they may become aggressive scavengers around human food, making them common around outdoor activities where food or drinks are served. Yellowjackets are particularly attracted to sweets and may become pests when food is served outdoors. They are also attracted to ripening or decaying fruit such as apples and raspberries, which also brings them into contact with humans. When dealing with nesting colonies around homes, ignore those nests that are up high in buildings or trees or otherwise located where the wasps do not come in contact with humans. These nests that people are now finding hang in trees or are attached to buildings. Most likely, they have been there since spring and have gone undetected until wasp activity drew attention to them. If these nests are close to human traffic, there is an increased risk of stings and they should be controlled. The best way to destroy wasps in these nests is to use a pressurized aerosol insecticide, often called “wasp and hornet killers.” Insecticides that are found in these aerosol products include tetramethrin and permethrin, tetramethrin and sumithrin, or talomethrin and allethrin. Products containing mint oil are also available. It has been reported to be effective against paper wasps, but it is unclear how effective mint oil would be against yellowjackets and baldfaced hornets. Wait until evening when the yellowjackets or other wasps are less active, and spray the aerosol insecticide directly into the opening where the wasps have been flying back and forth. For paper wasps which construct a nest made up of a single comb without a cover, treat the entire underside of the nest. Check the nest for activity and if there are still live wasps, repeat the treatment in a few days. Another common place for wasps to build nests is in holes in the ground. Pouring soapy water into the nest entrance can control these ground-nesting wasps. If soapy water does not eliminate the nest, insecticides that are effective include carbaryl, bifenthrin, cyfluthrin, deltramethrin, esfgenvalerate, or permethrin as a dust or liquid. Using the dust form of these products is generally more effective than the liquids. The most challenging type of wasp nests are those hidden behind steps, in wall voids or in other inaccessible areas. The wasps are often seen flying back and forth through a crack or small hole, but the nest is not observed. It is important not to seal the opening because the wasps will then seek an alternative exit which may be into the living quarters of the home. Aerosol insecticides are not effective in these situations because the nest may be located in a site far removed from the entrance opening. The best way to control a hidden nest is to apply permethrin (e.g. Bonide Ant Dust). When the entrance is obvious, the dust may be applied directly into the opening by putting the insecticidal dust in a plastic dispensing bottle and squeezing it into the entrance. This product may also be available in a ready-to-use squeeze bottle. As the wasps move in and out, the dust adheres to their bodies and they carry it to the nest. If there is a nest in the wall, but no entrance is found, it is probably best to contact an experienced pest control service to eradicate the hidden nest. When applying insecticides to a wasp nest, wait until evening when it is cooler and the insects are not actively flying in and out of the nest. Wear protective clothing to help prevent being stung by the insects. Always read all the directions and precautions on the label of the product you are using and follow them carefully. Keep in mind that wasp nests are annual and that they only survive for one season. Once we receive one or two hard frosts, the old queen and the workers will die. Newly mated queens leave their nests during late summer to seek sheltered sites for the winter. When they emerge next spring, they will construct new nests and begin to lay eggs to start a new colony.
