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Digger bees are solitary insects that resemble other kinds of bee species such as yellow jackets and honey bees. Unlike these other more social species, digger bees are not aggressive and live one bee per nest. Their nests, small mounds of dirt with a hole in the center, can be constructed closely together to create the appearance of a colony. If left untreated, the community can grow to take over your entire yard and jeopardize the safety of family and pets. Treatment is simple but time-consuming and it may take several seasons to fully eradicate the problem.
Identify the species of bee or wasp infecting the yard and make sure you are in fact dealing with solitary digger bees. Do this by watching the nest for a few days. If more than one bee is entering and leaving a hole, call an exterminator. These are a more aggressive species that could do a great deal of harm to you and your family. If only one bee is ever seen entering and leaving a hole, these are most likely digger bees that you can treat yourself.
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Count the holes. There are two different treatments for these pests that will depend on the number of nests you have to deal with. Less than 30 nests can be treated with a dusting method, while larger infestations will require a more blanket like treatment.
Fill a hand duster with deltamethrin dust, which is a white, talc-like powder that has no odor. Treat the area at night when the bees are in their nests by squeezing the duster three to five times in each home to ensure a thorough application and then plug the entrance with tapered cork plugs. Plugging the entrance will help ensure that the bees do not escape a lethal dose and that rain or irrigation will not wash away the chemical.
Treat excess adults that emerge from holes as you are plugging with an aerosol bee freeze pesticide and then treat the empty nest. Chemicals will not kill eggs, only hatchlings, so the longer chemicals can be left in the holes, the more insects will be killed. Expect to have more bees next season as eggs hatch but then repeat the treatment to remove all reproducing adults.
Use cyfluthrin granules for infestations of larger than 30 nests. These are odorless white granules that can be applied with a granule spreader. They are slow-acting and last a long time helping to ensure that the chemical lasts long enough to kill hatching bees. Cover the entire affected area with the granules.
Water the lawn and then immediately apply esfenvalerate over the top with a dial-a-mix sprayer. This is safe for people and pets and soaks into the nests to provide a residual path that will distribute the pesticide every time a bee comes in or out of the hole. The water will also activate the granule treatment and help it penetrate the nests.
Try to treat a nest immediately, especially in the spring, to make sure you are killing the young hatchlings and adults so that there is less chance for reproduction. Treatments in the summer and fall will only affect existing adults so you will need another treatment in the spring as the eggs hatch.
Though digger bees are generally not aggressive, they can sting and individuals with allergies could be particularly at harm.