by Rita Lynn
We hear a lot about the plight of the honey bee, its reduced numbers, and its susceptibility to diseases, Africanization, parasites and hive collapse. We also hear about the critical need for pollinators, being reminded that a third of our food supply and a third of the feed for our meat sources depend on bees for pollination.
Surprisingly, the majority of crop pollination is performed not by honey bees, but by native bees that do not produce honey. For example, of the 1700 bees trapped for a study in a West Virginia forest, only 34 were honeybees. The remainder consisted of a variety of native bees. In addition to native bees being more prevalent than we might realize, they are also much more efficient pollinators than honeybees. It takes about 360 honeybees to pollinate an apple tree, but just 6 native orchard mason bees can do the same job!
Like many native bee species, mason bees (Osmia spp.), also called orchard mason bees because of their emergence when fruit trees are flowering, are solitary creatures. They form their nests in proximity to other mason bees, but they do not interact with them. Each female bee is a queen, and she inhabits and maintains her own home. They are called by some “the gentle bee,” in that they rarely sting, and people can approach the nest without risk. If a mason bee should somehow be threatened enough to sting, the reaction is more like a mosquito bite than the sting of a honey bee or a wasp, and the sting does not trigger an allergic reaction in sensitive people. These factors make them the ideal “pet” pollinator for our urban gardens.
Mason bees will pollinate almost any flower within 100 to 300 feet of the nesting site. Early in the season, dandelions might provide pollen, but mason bees usually emerge just when the fruit trees need their services. The queen then gathers the pollen, lays an egg in her nesting tube and deposits pollen for nourishment. She then encapsulates that egg with a wall of mud. She continues this process of laying eggs, usually putting 6 to 10 in each tube. (As you might have gathered, this nest construction gives rise to the mason bee name.) The queen is able to lay eggs that will be female bees first, and then lay eggs that will develop as males closer to the opening of the tube. This process continues for the six-week lifespan of the queen. During the summer, the eggs develop into larvae and then small, egg-shaped pupae. The following spring, if they are developing in the wild, the male bees will emerge first and be available to mate with the females as their emergence follows.
My interest in mason bees stems from a display at Reiman Gardens two or three years ago. The exhibit demonstrated several simple methods for attracting these bees to yards and orchards. Specifically, mason bees have four crucial needs: pollen, mud, safe nesting tubes, and protective quarters for the nesting tubes. A fifth element – harvesting and storing the bee cocoons under refrigeration from fall until blossoming begins the following spring – could also be added for improving the likelihood that bees will survive over the winter.
With regard to nesting holes, mason bees use tubes with openings 5/16ths inch in diameter and a length of about 6 inches. In the natural setting, the bee might use a hollow reed or a woodpecker hole. To house them in our yards, we can provide holes made of paper or reeds. The pieces of bamboo that are often provided for that use are not ideal, because they cannot be opened for harvesting the cocoons without injuring them. Plastic drinking straws are also not recommended, because they do not allow good air circulation and promote fungal growth.
Numerous structures can serve as the protective home. The structure needs to be deep enough, or have a protruding roof, to protect the nesting tubes from the weather. You can buy relatively expensive wooden homes of several designs, you can construct a home from lumber using instructions provided in the sources below, or you can even use a mailbox or a large PVC pipe. The home then needs to be mounted on a solid, east-facing surface that is protected from wind, at about head height.