Treat yellowjacket nests too close for comfort

Entomologist Jeff Hahn advises homeowners to treat yellowjacket nests near areas of human activity in order to avoid stings.

August 10, 2006

Above average populations of yellowjackets are popping up in Minnesota this summer, and University experts advise homeowners to treat nests that are found close to areas of human activity.

Treating the nests will help prevent stings, says Jeff Hahn, an entomologist with the University of Minnesota Extension Service. Waiting to treat the nests will allow them to continue growing late into the summer, he adds.

Hahn blames the yellowjacket increase on Minnesota's warm, dry spring weather. It allowed queens to become active earlier. They began constructing nests and producing workers sooner than normal. As a result, nests are now large enough and yellowjackets abundant enough to be easily seen.

"And if yellowjacket nests are anywhere near where we are active, we risk being stung by them," Hahn said.

Yellowjacket nests can be found in exposed or underground spots. They are often found hanging under eaves or from the limbs of trees or shrubs, or in old rodent burrows. They may also take advantage of cavities in buildings, such as wall voids or the spaces in cinder blocks.

Nests are small at the beginning -- about the size of a softball -- but can get to be the size of a basketball or larger, according to Hahn.

Deciding how to treat a yellowjacket nest depends on where it's located. If it's high in a tree or in a site where there is no risk of stings, then it should be left alone, Hahn says. Freezing temperatures will eventually kill the occupants.

However, if the nest is located where there is human activity, the nest should be controlled to prevent stings. First decide whether you will hire a professional pest control service or deal with the nest yourself, Hahn says.

If you decide to treat a nest found out in the open, Hahn suggests the following tips:

• Choose one of the widely available wasp or hornet spray products with active ingredients such as resmethrin, tetramethrin, permethrin, or prallethrin.
• Wait until evening to spray the nest. Yellowjackets are not very active when it is dark.
• Spray the insecticide directly into the nest entrance, located on the bottom.
• Check it the next day.
• If there is still some activity, treat again.

Yellowjackets found nesting underground can prove more difficult to treat. If you opt for the do-it-yourself method, Hahn recommends the following tips:

• Treat at night, just like you would for nests that are out in the open.
• Instead of using an aerosol can of wasp spray, use an insecticide that is labeled for insects in grass. Dusts work better than liquids, but it's harder to find dusts that are labeled for treating underground yellowjacket nests.
• Once you are sure all of the yellowjackets are dead, fill in the burrow with dirt.

According to Hahn, the most challenging type of yellowjacket nest to control is the kind located within structures, such as wall voids or attics. Because this type of nest is difficult to eradicate, it is usually best to contact a professional pest control service, he says.