Jeffrey Hahn, Extension Entomologist
The early spring has contributed to an above average number of yellowjackets this summer. Yellowjackets can be found nesting in a variety of different places, depending on the particular species. They range from aerial nests, e.g. hanging from tree limbs or the eaves of homes to subterranean nests, e.g. nesting in old mouse burrows to nesting in various voids in buildings. These nests, especially the cryptic ones, are present all season, but may not be noticed until late summer when the workers are more numerous.
Photo 1: Aerial yellowjacket nest. Jeff Hahn.
If a yellowjacket nest is located in a site away from human traffic and is not a risk for stings, then just ignore it. Yellowjackets are beneficial because of the insects on which they prey. All of the inhabitants of the nest will eventually die in the fall when freezing temperatures arrive. If however, the nest is located somewhere where people could get stung, then the nest should be eliminated. There are some situations where you can eliminate the nest yourself. A professional pest control technician is always an option any time you do not want to deal with a wasp problem.
Nests that are out in the open are fairly easy to deal with. Wait until dark when the wasps are much less active. Use an aerosol can of insecticide, something that is labeled for wasps and hornets (or something similar) and spray into the opening. Check the next day to see how effective the treatment was. If you still see wasps flying, repeat the spray the following evening.
Photo 2: Ground-nesting yellowjacts. Jeff Hahn.
Yellowjackets nesting in the ground are more challenging. You do not see the nest itself but you see an opening in the ground where they yellowjackets fly in and out. It is not unusual to walk by a nest in the ground all summer without knowing it is there. Then one day, the yellowjackets will react to a disturbance, e.g. mowing the lawn, and will come out to vigorously defend their nest. The most effective way to control a subterranean nest is with a dust labeled for ground dwelling insects (e.g. Bonide Eight Garden Dust), although these dust formulations are generally difficult to find. Apply it at the entrance of the nest at night when yellowjackets are less active. Check after a day to see how effective the treatment was and repeat if necessary. Another option is to use a liquid insecticide, pouring into the nest entrance, but this is less effective.
Photo 3: Hidden yellowjacket nest in home. Jeff Hahn.
The most challenging yellowjacket nests are those found inside homes in wall voids, attics, concrete blocks, or similar spaces. You can not see the nest, similar to a subterranean nest, but you can see the workers flying in and out of an opening or crack. These nests are very difficult for a homeowner to control on their own. A dust labeled for use in homes is the most effective or a foam formulation, but unfortunately these products are generally not available to the general public. A liquid aerosol, while readily available, is generally not effective. Sometimes an aerosol spray can cause the yellowjackets to look for another way out, which often leads them to the inside of the home. Also, don't seal the nest opening until you know all of the yellowjackets are dead as you can cause the same reaction. The best method to control hidden nests in buildings is to have a professional pest control company treat the nest.
Photo 4: Close up of photo 3. Jeff Hahn.
Remember that yellowjackets are annual nests, i.e. the old queen and the workers only live until the weather gets below freezing, then they die. If you are dealing with a yellowjacket nest late in the season, it might be easiest to wait until the cold temperatures kill them. Nest are also not reused the following spring.