Mason Bee
Tiny metallic blue-black, mud-sealed holes in wood or stems
Individual
Swarm
Nest / Hive
Wing / Body Pattern
What It Is
Mason bees are small, solitary native bees in the genus Osmia, found across Middle Tennessee. Mason bees are solitary, so each female nests alone. There is no queen, no colony, and no hive, and there is nothing to remove. Size: 1/4 to 1/2 inch, noticeably smaller than a honeybee.
How to Identify
Body: metallic blue-black or iridescent blue-green, compact and fuzzy, with a distinctive metallic sheen. Nest: mason bees use pre-existing holes rather than drilling their own. They nest in hollow plant stems, existing holes in wood, gaps in masonry, or bee houses. Each female lays eggs in a tube and seals the entrance with mud, and that mud-sealed hole is the clearest nest identifier. For most species, activity is a brief spring window, roughly four to eight weeks.
Behavior and Risk
Mason bees are among the least defensive insects a homeowner will meet. Females can sting if handled directly but rarely do, and males cannot sting. With no colony to defend, the motivation behind most bee stings is simply not present, so sting risk in a normal residential setting is effectively zero.
How to Handle
Mason bee activity needs no handling. If you see small metallic bees coming and going from holes in wood or from a bee house in the garden, this is a beneficial visitor, not a problem. Do not treat the nests and do not fill the holes during spring while bees are active. To encourage mason bees, install a mason bee house in a sunny, south or east-facing spot.
Mason bees are tiny and metallic blue-black. They use existing holes and seal them with mud. Carpenter bees are large, drill new clean round holes, and have a shiny black abdomen. If the bee is small and metallic and the hole has a mud seal, it is a mason bee.
Frequently Asked Questions
Are mason bees dangerous?
No. Males cannot sting. Females can sting if handled directly but are highly unlikely to do so. There is no colony to defend.
Why do mason bees seal their holes with mud?
Each female lays eggs in cells within the tube and provisions each cell with pollen for the larvae. When all the cells are complete, she seals the entrance with mud to protect the brood.
How can I help mason bees?
Install a mason bee house with the right-diameter holes in a sunny, sheltered location. Plant early-blooming flowers for spring nectar and pollen. Avoid pesticide use near nesting sites and flowering plants.
Does Beecasso remove mason bees?
Mason bees are solitary, non-aggressive, and ecologically valuable. There is no hive or colony present. If you are not sure what you have, send us a photo.
Found small dark bees going into holes in my wall. Is that mason bees?
Possibly. If the holes are small, pre-existing, and the bees are tiny and metallic blue-black with a mud seal on the holes, that is likely mason bees. If the holes are large clean round holes being drilled by a large bee, that is a carpenter bee. If bees are entering through a gap in large numbers with two-way traffic, that may be a honeybee colony. Send us a photo.