Blue Orchard Bees

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Biology & Management

What are they?

Blue Orchard Bees (BOBs) are native North American bees. They range throughout most of the United States and southern Canada. They are also called “orchard mason bees” and scientists know them as Osmia lignaria. They are beautiful insects, about 1.3 cm (0.5 in.) long and blue-black with a metallic sheen. Unfortunately, they are sometimes mistaken for large flies. (Look closely—they have 2 pair of wings and are not interested in garbage!) The females are somewhat larger than the males and the males have a white, hairy face. Like all bees, mason bees collect flower pollen as a protein source for their young and get their energy from flower nectar. In shopping for their "groceries", they carry pollen from flower to flower, achieving pollination.
A number of things set BOBs apart from other bees:

Solitary but Like Company

They are loners--each female bee builds a nest by herself cell by cell, lays eggs, seals the nest, and then repeats the process. She receives no help from other bees, so there is no colony or “hive” as in honey bees or bumble bees. But despite this, BOBs are attracted to each other—they like to build their nests together in aggregations.

Build with Bricks

Like the wisest little pig, BOBs build their nests with bricks (sort of). Each egg chamber in the nest is sealed with a partition of ordinary mud. The entire nest is also sealed with a hardened mud capping. This is why they are called “mason” bees.

"Instant Bees"

Mason bees develop as larvae through the summer and turn into adults in the fall. Then they rest during the winter, ready to emerge at the first sign of blossoms in the spring.

Perfect Pollinators

many varieties of apples, cherries, plums, peaches, and similar stone and pome fruits. Because they specialize on these plants, they are exceptionally good at pollinating them. They will forage on other flowers as well. They are adapted to a cool climate and can fly in chilly, even drizzly weather. Thus, they can be busy pollinating when honey bees remain inside the hive. Individually, a female mason bee is several times as efficient as a honey bee worker in pollinating fruit trees. These features make BOBs the perfect pollinator for those who have a small number of trees or bushes but may not want to manage honey bee hives.


As with other solitary bees, BOBs are gentle and shy. The female has a stinger (actually it is an egg guide), but she uses it only when in serious danger, as when she is purposely caught in the hand. Mason bees do not attack to defend their nest or arouse each other in alarm but simply flee when disturbed. Therefore, they are totally safe, even around children and pets.

Keeping Blue Orchard Bees

Female mason bees make their nests in hollow cavities. In nature, these are found under the bark of trees or in the emergence holes of tree-eating grubs. They adapt well to man-made environments and frequently nest under shingles and siding. Mason bees can be attracted to your yard—they may already be in your neighborhood, especially if you have a garden with fruit trees or berries. To make mason bees a permanent part of your home orchard, simply provide them with nest holes and make sure they have plenty of flowers to feed on. The ideal nest hole is 8 mm (5/16 in.) in diameter and 7.5 to 15 cm (3 to 6 in.) deep. The bees will nest in a wide variety of such cavities: straws and holes drilled in boards are commonly used. But to produce happy and healthy bees and to avoid disease build-up, you should give the bees quality housing. This means a dark, closed-bottom cavity with smooth, porous walls that can be renewed each year. Mason bees are a fascinating wild creature that can be easily encouraged to colonize the backyard garden environment, to the benefit of the gardener, orchardist, homeowner, and nature lover.


Blue Orchard Bees have problems, just like all creatures. They have certain requirements in nest placement, preferring a warm, dry, situation. They must have adequate flowers to raise their brood. And finally, they are subject to diseases, parasites, and predators. These include fungal diseases of the developing bees, various types of mites which compete with the larval bees for food or eat the bee larvae, a variety of parasitic wasps, spiders, and larger predatory animals like woodpeckers, crows, and squirrels.

Entomo-Logic Straw System—the Best You Can Do for Your Blue Orchard Bees

Bare wood holes are acceptable to mason bees, but over time they become fouled with debris, germs, and parasites. If not cleaned, the hole subsequently loses its attractiveness to the bees as a nest cavity. Mason bees tend to “go away” from such nest boxes after the first year or two. Diseases and parasites may build up in unhygienic nest boxes. The best nest system for orchard bees is a smooth wood hole with a porous insert or liner that can be replaced each season. This is the Entomo-Logic Straw System. The concept of straw inserts was developed by USDA scientists. We have perfected the system and offer custom-made straw inserts and carefully crafted wood boxes. The boxes are easy to maintain—simply remove the filled nests in the fall and replace them with clean inserts for the next spring. The new bees in their nests can be stored safely until it is time for them to begin the nesting cycle and pollinate. Then, simply place the nests near the nest boxes and allow the bees to emerge and re-nest in the new inserts.

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Frequently Asked Questions

Q Where do I put the nest box?
A The ideal place is on the south or east side of a structure (house, garage, shed, etc.) under the eaves. The box should be protected from rain and wind and should receive morning sunshine. Put the box up high out of the reach of pets and children. On a 2nd or 3rd story is fine if you have a balcony or deck. The bees will find flowers to pollinate up to 200 m (600 ft.) yards away, although the closer they are to their food plants, the better. DO NOT put the box in the open or under a tree unless there is no suitable structure for a long distance. Sometimes hanging the box on a fence works.

Q What do I do with the mason bees when they arrive?
A The bees will be diapausing (~hibernating) in their cocoons in the nest tube when you receive them. Refrigerate them until spring or keep at outdoor (cool to cold winter) temperatures. Then release them near the nest box. See our leaflet "How to Care For and Use Entomo-Logic Blue Orchard Bees" for more information.

Q How do I set out the bees to pollinate?
A Three days to a week before bloom begins, put the nest tubes or loose cocoons in your Entomo-Logic Ship/Release box and attach to the bottom of the nest box. If you do not have a Ship/Release box you can use a container such as a juice can or paper bag with a 9-mm (3/8-in.) exit hole. Attach the container adjacent to the nest box so when the adult bees emerge they can crawl up onto the box to sun bask and mate. DO NOT put the occupied nest tubes in the nest box—put only fresh (empty) straw inserts in the box for the new nests the emerging bees will make.

Q What do I do with the filled nests?
A The developing larvae in their straw-lined nests are very fragile. They will develop in summer over the course of 2-3 months. You may either leave the nest box undisturbed during this time or gently take it down and store it in a warm, safe place sheltered from vibrations and predators. By the end of the mason bee flight season (around June 1st ), you may notice deterioration of the nest plugs or many tiny parasitic wasps around the box--these are good reasons to move the box to safety. By autumn (usually September) the new generation of mason bees has matured into adults in cocoons and can be handled safely. At this time or later, remove the filled nests from the box, discard any empty or suspicious looking nests, and refrigerate healthy nests until the following spring. The Entomo-Logic Ship/Release box makes an ideal storage container. See our leaflet "How to Use the Straw Insert System" for more info.

Q Do BOBs sting?
A As with all bees, the female blue orchard bee has a stinger, actually an egg guide, which she may use to defend herself. However, because they are solitary and extremely shy, mason bees will not sting unless handled directly. Since they are also wary and fast, it is unlikely you will ever be stung by a mason bee. The sting is somewhat less painful than that of a honey bee. Because the sting shaft has no barbs, the female mason bee survives after stinging and can sting again. Male BOBs have no stinger.

Q Will BOBs pollinate my avocado-orange-lemon-macadamia-loquat-etc. tree?
A The orchard mason bee, Osmia lignaria, has a strong preference for the pollen of cherries, apples, plums, pears, and many other pome and stone fruits and berries in the family Rosaceae. This is what makes them very efficient pollinators of these fruits. The bees will seek out and concentrate on such flowers. But they are also known to collect pollen from many other plants. (Pollen is the only source of protein for the developing bee larvae.) The bees will visit an even wider variety of flowers for nectar, their energy source. Some of their favorite nectar flowers include rosemary, garden kale, and Phacelia, but other species may be visited. Obviously, the bees can only visit flowers that bloom during their flight season, which lasts about 2 months. We can not guarantee that the bees will visit the flowers of your favorite plant but suggest you try them out. Keep in mind that other wild bees that take up residence in the nest box may also pollinate the target crop (see below).

Q What else lives in the nest boxes?
A Depending on where you live, the nest tubes may be used by other species of Osmia (other “mason” bees), leafcutting bees, potter wasps (beneficial caterpillar hunters), or by other species. Most insects that nest in the boxes are beneficial except the parasites that live on them. Mason bees are usually the first to colonize the box but are often followed by leafcutting bees if the box is left hanging and there are uncolonized holes.

Q Will BOBs live in my area?
A The Blue Orchard Bee, Osmia lignaria, is native to most of North America except the desert southwest and parts of the southeastern Gulf states. The species thrives in temperate climates (cold to cool winters) and in mountainous regions. They are an adaptable species and may be abundant in suburban areas and around farms near wild habitat.

Q Do BOBs have mites?
A Mason bees are becoming popular partly because of the problems honey bees are having with two parasitic mites, the internal tracheal mite and the external varroa mite. These mites are specific to honey bees and have no effect on mason bees. However, mason bees have many pests, parasites, and diseases of their own, including some mites. Proper management of your bees using the straw insert system to give the bees fresh nest material each year is the best way to discourage build-up of these destructive organisms. “Pollen Mites” a.k.a. “hairy-footed mites” can be controlled with extra management procedures (contact us for up-to-date information on this.)

Q How do the bees get out of the nest?
A Male eggs are laid toward the nest entrance, so they emerge first. They jostle and arouse each other and come out in succession. Females follow several days later. If one bee dies, those below chew their way through it.

Q How do I get the honey out?
A Sorry! Mason bees don’t make honey! They collect nectar from flowers but they burn it up immediately in their nest-building and brood-rearing activities. Because they are inactive during the winter, they do not need to put in winter energy stores, as do honey bees, who are active all year. But mason bees are excellent pollinators—they make FRUIT…ENJOY!

More detailed answers to these and many other questions may be found in the illustrated, information-packed booklet:

Bosch & Kemp cover

How to Manage the Blue Orchard Bee
by USDA bee researchers Dr. Jordi Bosch and Dr. William Kemp.

Order it through our retailer, Raintree Nursery

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