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Summer Leafcutter Bee


Both spring mason bees and summer leafcutter bees are gentle, solitary, gregarious, hole-nesting bees that are great alternative managed bees. They are superior pollinators that carry pollen dry and loose on their abdomens.

  • Spring: the mason bees that we carry emerge in cool spring weather (50F/10C), use clayey mud to build nest walls, spin cocoons, and hibernate as fully-formed bees. They are superior pollinators of apple, cherry, pear, almond, peach, kiwi, nuts, and berries and of other early spring-blooming flowers. 
  • Summer: leafcutter bees emerge in warm summer weather (70F/21C), build protective cocoons out of leaves, and hibernate as larvae. They are superior pollinators of melons, squash, cucurbits, peas, and other summer vegetables and flowers. 

In Lifestyle, Habitat & Pollination, you learned about the characteristics that are common among our spring mason and summer leafcutter bees. Now it’s time to learn about what makes each bee unique and why they make such great companions in your backyard.

Spring Mason Bee

Spring Mason Bees

Blue Orchard Mason Bee (Osmia lignaria)

Mason bees are one of the nearly 4,000 bees that are native to North America. They are the original, and best, pollinators of our early blooming spring fruit and nut trees and berry bushes.



SPRING pollinator that emerges when the weather reaches a consistent daily temp of 55F/13C. Don’t worry, nighttime temperatures don’t affect when the bees begin to emerge. Mason bees often emerge around the same time that dandelions and cherries begin to bloom.


Spring fruit and nut trees such as apple, cherry, pear, peach, kiwi and almond; and spring berries like blueberry, strawberry, currant, and gooseberry.

Nest-building Material

Mason bees need moist, clayey mud for building their nest walls. The extra thick layer of clayey mud at the end of the nesting hole is called a capped end.

Areas with sandy soil, like beaches and deserts, are not able to support mason bees without a supplement of clayey mud. If a mason bee can't find clayey mud, they will nest elsewhere. You can provide a hole in the ground with our mason bee mud and we also have a mud box that keeps mud moist in arid locations.


Immediately after being laid, the egg hatches and the larva begins to consume its pollen loaf. The larva relies on warm temperatures to grow, spin a cocoon, and transform into an adult that hibernates through the winter.


By the end of summer, larvae have spun waterproof cocoons. The bees overwinter as fully-formed adult bees in brown cocoons, which look similar to fuzzy raisins.


Blue orchard mason bees (Osmia lignaria) are a deep metallic blue or teal. Hornfaced mason bees (Osmia cornifrons) are a medium brown with dark brown stripes (these bees are extremely similar to blue orchard mason bees in their life cycle and nesting habits).

Identifying Genders

Males: emerge from cocoons first, can be half the size of female bees, and have long antennae. Their white mustaches are easy to identify. Males don't nest inside of the nesting holes but they typically wait for females near the nesting house.

Females: they have shorter antennae and large mandibles (jaws) that they use to gather and carry mud. Females wait out bad weather and usually spend the night in their nesting holes.

Life Cycle of Mason Bees

  1. Early Spring: Adults emerge from cocoons and mate. Males are only actively flying for two weeks.
  2. Spring: Females gather pollen and nectar, build mud walls, seal up nesting hole ends with clayey mud. Females actively fly for up to 6 weeks.
  3. Late Spring-Fall: Eggs hatch and grow, slowly eat pollen loaf, spin dark brown cocoons.
  4. Fall-Winter: Hibernate as fully-formed adults. Adults live off their stored fats over the winter.

Summer Leafcutter Bees

Megachile rotundata (Alfalfa Leafcutter Bee)

Naturalized after 1940, alfalfa leafcutter bees saved the American alfalfa industry because they are 15 times better at pollination of alfalfa than honey bees. Alfalfa is a very important high-protein feed for livestock. Leafcutter bees are also good pollinators of milkweed, the host plant of the monarch butterfly, whose population is threatened but not currently protected as an endangered species.

Note: If you are a Canadian resident please order through Crown Bees Canada


SUMMER pollinator that begins to emerge after consistent daily temperatures of 75°F (24°C). Don’t worry, nighttime temperatures don’t affect the bees’ emergence.

Summer leafcutter bees are special because they are biovoltine: they are able to produce two broods (and sometimes more!) per season. Some of the eggs develop quickly and emerge as adults in the same season as they were laid, these are called second generation bees. Second generation bees will emerge if you leave filled nesting holes in a warm location and the weather is warm enough for long enough.

The evidence of the emergence of second generation bees is a large hole in capped ends and leafy debris at the bottom of the nesting house. Second generation bees give your garden a boost of even more pollination time! Unfortunately, with each extra generation, the amount of bees nesting in your trays will diminish as bees also disperse to other nesting sites in the area. You may need to supplement with a new order of leafcutter bees every few years.


Generalist pollinator of summer flowers and vegetables such as melons, peas, squash, tomatoes, beans, and sunflowers.

Nest-building Material

Females use their mandibles (jaws) to cut circles into leaves and these small ¾” cuts into your non-fibrous plants will not harm the plant. Leafcutter bees prefer leaves similar to those of rose, lilac, hosta, and pea leaves. Female bees use the cut circles to build a protective leafy cocoon for the larva. She places a pollen loaf and egg inside and seals both into the leafy cocoon. Leafcutter cocoons are beautiful and are sometimes made of flower petals. At the end of the nesting hole the female bee packs in a capped end of extra leaves or petals to protect the developing larvae.


Some eggs go into winter hibernation (also known as diapause) and do not develop into adults until the following warm weather of late spring. Some eggs hatch right away, consume their pollen loaf and become adults in the same summer they were laid. Bees that emerge in the same summer they were laid are called second generation bees. Incubation requires 3 to 7 weeks of warm weather (70°F-85°F/21°C-30°C) with daytime temperature playing a large role in determining the speed of development. When you buy leafcutter bee cocoons from Crown Bees, we incubate them for you and they arrive at your home ready to pollinate your garden.


The protective outer layer of the cocoon is made by the adult female bees from leaf bits, leaf juices, and bee saliva. Leafcutter bees overwinter as eggs or larvae and they finally pupate when the weather warms in the early summer. Larvae will eat the leaves on the interior of the cocoon and leave the outer layer of leaves intact. Within the outer layer of leaves the larvae spin a thin, fibrous cocoon. Leafcutter cocoons are not waterproof and should not be washed.


All bees have two sets of wings for a total of 4 wings, hairy bodies, and large oval-shaped eyes that are similar in appearance to ants, which are distant relatives. Alfalfa leafcutter bees are black with pale yellow stripes on the abdomen and face. At less than half an inch long they are the smallest of the leafcutter bees.

Identifying Genders

Males: emerging first, males are about ¼ to ⅓ smaller than female bees. The easiest way to identify them is by their bright green eyes and a white patch of hair on the top of their head that sometimes looks like a mohawk. Their bodies are rounder and brighter than female leafcutter bees. About two weeks of a male leafcutter bee's life span is spent as a flying adult.

Females: emerging up to two weeks later than males, females are larger, darker, and their bodies are flatter than males. Their eyes are black and they have large mandibles (jaws) needed to cut leaves. The underside of their abdomen is covered in furry white hair that is perfect for collecting pollen from nearby flowers. When peeking into nesting holes their faces have a “V” of light hair. Females have a flight time of about a month and with cool or poor weather this time can be extended up to 6 weeks.

Life Cycle of Leafcutter Bees

  1. Summer: Adults emerge from cocoons and mate. Cocoons delivered by Crown Bees have been incubated and arrive ready to emerge. Bees raised by you will emerge based on how much warm weather they receive. Males are only actively flying for two weeks.
  2. Summer: Females gather pollen and nectar, build protective leafy cocoons, and seal up nesting hole ends with extra thick caps. Females actively fly for up to 6 weeks after emerging from their cocoons.
  3. Summer: If conditions are right (many days of hot weather), some bees will incubate and develop into adults right away. These second generation bees mate and continue to fill your nesting holes with next year’s bees.
  4. Late Summer-Fall: Eggs and larvae enter diapause (hibernation) within their protective leafy cocoons.
  5. Winter: Hibernate as larvae.
  6. Spring: Larvae begin metamorphosis to become adult bees.