Bug of the Week May 4, 2009

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Previous episodes of Bug of the Week examined the plight of our honeybees, explored the fascinating behaviors of carpenter bees, and detailed the diligent digging of plasterer bees. This week we turn our attention to another industrious member of the bee clan, mason bees. Mason bees are solitary bees. Solitary means that they do not live in colonies with queens that lay eggs and workers that cooperate in the raising of young as do honeybees and bumble bees. However, mason bees do recognize a good thing when it comes to housing. Let me explain. Two weeks ago, a colleague gave me a bunch of cardboard tubes about ¼ inch in diameter and six inches long and told me that these magical tubes would attract large numbers of mason bees. His instruction to place the tubes outside was accompanied by the assurance that they would soon be inhabited by mason bees. The “build it and they will come” strategy had me skeptical, but I bundled several with an elastic band and dutifully placed them on a pile of unused firewood. Within days, mason bees discovered this perfect condominium and the scuffle for occupancy began. I had mason bees by the dozen. In the wild, mason bees evolved to take advantage of natural cavities in soil, plant stems, or wood or in galleries made by other insects such as wood-boring beetles. Some species even build their nest in vacant shells of snails. In the spring, female bees gather nectar and pollen from blossoms of trees and shrubs and carry it back to the nesting site. A dense brush of fine hairs called scopa cloak the underside of the bee’s abdomen and are used to collect and transport pollen. Back at the tubular condominium the mason bees disappeared into the holes and reappeared with surprising regularity. An interesting account of the mysterious events in the gallery of the mason bees was reported by Phillips and Klostermeyer. The female enters the gallery head first and at the end of the void she deposits a droplet of nectar. She then does a somersault within the gallery or backs out of the tunnel and reenters backwards. A quick moonwalk brings her back to the glob of nectar. Using her hind legs, she brushes pollen from the scopa lining her body onto the nectar droplet. The pollen and nectar are mixed and formed into a ball that serves as food for her developing babes. If the female has mated, she will choose the sex of her young and lay an egg that will develop into a son or daughter. How’s that for control? If a daughter is the goal, a larger pollen ball will be prepared as females are generally larger in the world of mason bees. Sons are smaller and require smaller provisions. Unmated females produce only sons. It may take more than 30 trips back and forth to flowers and the nest to gather provisions for each offspring. Once the pollen ball is constructed and an egg deposited, the chamber is sealed with a small plug of mud or clay – hence the name mason bee. Upon opening one of the cardboard tubes, I discovered more than a dozen chambers each with a pollen ball and larva merrily devouring the pollen cake. In addition to being highly entertaining, mason bees provide valuable ecosystem services by pollinating a variety of plants including ones that bear some of my favorite fruits such as apples and blueberries. Like many other bees we have met in Bug of the Week, mason bees are gentle and not very keen on stinging humans. I handled several adults, received a couple of cautionary bites, but never was stung. Nesting materials for mason bees can be purchased commercially and I highly recommend creating habitats for these fascinating native pollinators.

We thank Lee Hellman for inspiring this Bug of the Week. The interesting account of mason bee behavior came from an article by Joel Phillips and E.C. Klostermeyer, “Nesting behavior of Osmia lignaria propinqua”. The remarkable reference “The Bees of the World” by C.D. Michener was also used in preparation of this episode.

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