WSU Extension

Pestsense

Orchard mason bees

(revision date: 6/5/2024)


Use Integrated Pest Management (IPM) for successful pest management.

Biology
Orchard mason bees are black to metallic blue bees and are slightly smaller than a honeybee. They are often mistaken for house flies, because they may enter houses and be found in sunny windows in the early spring. However, you can easily distinguish them from flies because orchard mason bees have four wings while flies have only two wings. Orchard mason bees are solitary bees, earning their name “mason” by using mud to make their nests. They do not excavate nesting cavities in wood; rather, they use existing holes left by other insects, nails, between or beneath shingles, etc. They are not structural pests, though they may be seen examining siding or shingle roofs in search of suitable nesting sites. Orchard mason bees are short-lived, emerging from their nesting holes when temperatures are favorable usually around mid-March through May. The females collect pollen and nectar, lay a single egg in each cell in the nest hole, and then die. The next generation overwinters in the nest holes till they emerge the following spring. Orchard mason bees are active at lower temperatures than honeybees, making them especially important for pollination of early spring-blooming fruits and flowers. These are very gentle bees, rarely stinging unless handled roughly or trapped under clothing and pinched. The sting is reported to be very mild.
Management Options

Non-Chemical Management
  • Bees in the home may be removed by trapping against the window in a dry glass or jar, sliding a card over the opening, then releasing outdoors. Persons severely allergic to bee stings should use caution, although the likelihood of being stung by an orchard mason bee is very slight. Bees can also be removed by vacuuming.
  • Fill nail holes and other openings in siding which may attract bees (1/4” to 3/8” in diameter) if nest-building is a nuisance. Orchard mason bees are not structural pests, but will use existing holes for nest-building, including those made by other insects.
  • You can encourage orchard mason bees by providing nesting sites. “Bee boards” or nesting sites are commercially available or you can make your own. For more information on encouraging a local population of orchard mason bees, please contact your local Extension office.
  • To discourage bees from entering the house, maintain effective, tightly-fitting window and door screens.
Select non-chemical management options as your first choice!

Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

No control measures are recommended for this insect. These are beneficial pollinators and should be encouraged whenever possible. However, all bees are extremely susceptible to pesticide poisoning. For more information, see PNW 591 How to Reduce Bee Poisoning.

Images
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Caption: Orchard mason bee
Photo by: Art Antonelli