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Look out for wasp nests!

Now is a good time to be watching for wasp nests around your home and yard and garden. The best options for controlling a wasp nest depends on where you find it.

The first option to consider is ignoring it. If the nest is located away from human activity and stings are minimal, leave it alone. When freezing temperatures arrive in fall, the queen and all of the workers are killed; they do not survive the winter. If you can wait until then, your best option is to do nothing.

However, if there is a risk of stings and October or November is too long to put up with them, then treat the nests. There are three general wasp nest situations: exposed nests, ground nests, and hidden nests. Each is controlled a little differently.

Exposed wasp nests

An exposed nest is one that hangs from a horizontal surface, such as the eaves of a home or the branch of a tree.  Treating this kind of nest is a
An aerosol can of wasp spray is all that is needed to treat
an exposed nest.  Photo: Jeff Hahn, U of  MN Extension
straightforward task that residents can do themselves.

Use an aerosol can of insecticide labelled for wasps and hornets and spray into the nest entrance.  However, do this during late evening when wasps are no longer flying in and out of the nest. One application is usually all that is necessary to eliminate them; if there are survivors retreat the nest.

Ground-nesting wasps

Wasps also commonly nest in the ground, especially in old rodent burrows. You can see the opening that leads to the nest but you can’t see the actual nest itself. These nests are not easily found; it is not unusual for people to first notice these nests during late summer.

Use a dust to treat ground nesting wasps.
Photo: Jeff Hahn, Univ of MN Extension
The best control is to apply a dust or granular insecticide to treat the nest. Again, do this during late evening when wasp activity has stopped. Don’t use liquid products as they are less effective.

Hidden wasp nests

Nests concealed inside buildings are very challenging. Like ground nests, all that is visible is the space where the wasps fly back and forth but the actual nest can not be seen. It is common for wasps to nest in wall voids, attics, spaces under stairs and similar sites.

Don’t spray the nest opening. This is not effective as the nest does not line up where this opening is located, so the insecticide does not actually get into the nest and affect the colony. Similarly, don’t plug up the opening to try to prevent the wasps from getting out.
Hidden nests are the toughest to eliminate.
Best to use a professional to control it.
Photo:  Jeff Hahn, U of M Extension

In both cases, the wasps will just go another direction, which too many times means into the inside of your home. It is common for people to be suddenly inundated with lots of wasps after sealing or spraying a nest opening.

The best control is to apply a dust into the opening. This product must be labeled for use in and around homes. One common example is Bonide’s Spider & Ground Bee Killer.

Consider a professional

It is always an option for residents to hire a professional pest control technician to treat any wasp nest anytime they would rather not deal with it themselves. This is especially true for hidden nests which are very challenging to treat.

For more information, see Wasps and bees.

Jeffrey Hahn, Extension Entomologist
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