Mason bees are solitary insects and exceptionally effective pollinators. Each female bee builds her own nest, and a mason bee house provides the necessary pre-made cavities for her to lay her eggs. Understanding the timing of their emergence is the single most important factor for success when setting out a bee house.
Understanding the Mason Bee Lifecycle
The life of a mason bee operates on an annual cycle, beginning with a long period of overwintering inside a protective cocoon. During this dormant phase, the fully formed adult bee rests within the cocoon. The bee relies on the consistent cold of winter to remain in this state of diapause, conserving energy until spring.
The emergence phase is triggered by warming temperatures, typically when daytime highs consistently reach 50–55°F (10–13°C) or above. Males emerge first, often a few days before the females, and wait near the nest site for mating. Once mated, the female begins her short but industrious foraging and nesting period, which lasts only four to six weeks.
The female collects pollen and nectar, packing them into the nesting tubes as a food source before laying a single egg. She then seals the cell with a mud partition, repeating the process until the tube is full. Inside these sealed cells, the eggs hatch into larvae, consume the food, and spin their own waterproof cocoons by late summer, beginning the cycle anew.
Optimal Timing for House Placement
The timing for installing the mason bee house is crucial because it must be ready before the bees emerge from their winter cocoons. The exact window is late winter to very early spring, generally from February through mid-March, depending heavily on the local climate. Placing the house out during this period ensures the bees have a home immediately available upon emergence.
The house needs to be mounted before temperatures consistently stay above 50–55°F, which signals emergence. If installed too late, the bees may emerge and disperse to find other natural nesting sites. Installing the house too early risks exposing the nesting materials to unnecessary moisture and weather damage.
The best practice is to monitor the weather and local flora, looking for the first early-blooming plants like crocuses or dandelions. Placing the house out just as fruit tree blossoms begin to swell provides the perfect timing, ensuring the bees have both shelter and an immediate food source. This timing may range from February in warmer areas to late March or early April in colder regions.
Key Factors for House Location
Selecting the correct physical location for the house is important. The structure should be mounted on a flat, stable surface, such as a sturdy wall, fence post, or shed, to prevent it from swinging in the wind. A wobbly house can dislodge the mud partitions the female uses to seal her nesting cells.
The house should face east or southeast to capture the maximum amount of morning sunlight. Mason bees are cold-blooded, and the warmth of the early sun is necessary for them to raise their body temperature above 90°F (32°C) so they can fly and begin foraging. Afternoon shade is beneficial, especially in hotter climates, to prevent overheating the developing larvae inside the tubes.
It is necessary to shelter the house from direct rain by placing it under an overhang, eave, or roofline. Excessive moisture can lead to mold and fungal growth inside the nesting tubes, which can kill the developing cocoons. The house should be mounted at a height of approximately three to seven feet off the ground to deter pests and protect the tubes from ground splash-back.
What to Do After Nesting Season
Summer Storage
Once the nesting season concludes, typically by late spring or early summer, the tubes will be sealed with mud plugs. The occupied nesting material must then be protected through the summer and winter to ensure the survival of the next generation. The entire nesting block or set of tubes should be gently removed from its outdoor house.
The filled tubes should be stored in an unheated location protected from the elements, such as a shed, garage, or cool basement. This storage allows the summer development phase to occur at natural temperatures while preventing damage from rain, predators, and parasitic wasps. The cocoons will fully develop into adult bees inside the sealed tubes by the fall.
Winter Cleaning and Storage
Between late fall and early winter, the cocoons should be harvested from the nesting material, cleaned, and then placed in a cool, dark environment, like a refrigerator, until the next spring. This annual cleaning process removes pests, parasites, and diseases that accumulate over the season. It is important to replace or thoroughly clean the nesting materials annually to maintain a healthy environment for the emerging bees.