Tuesday, May 24, 2011

Eastern Carpenter Bee (Xylocopa virginica)

My carpenter bees have returned. Can it truly be summer without these sweet garden visitors?

Eastern Carpenter Bee (Xylocopa virginica)

Order: Hymenoptera (hy-men-OP-ter-a)
Family: Apidae
Subfamily: Xylocopinae
Genus: Xylocopa
Subgenus: (Xylocopoides)
Species: X. virginica
Common Names: Eastern Carpenter Bee, Wood Bee

Appearance: Carpenter bees are often confused with bumble bees (Bombus). Bumble bees are generally fuzzy and often have bands of yellow on their bodies. Carpenter bees, specifically the Eastern Carpenter Bee, can be clearly identified by their slick, shiny, black abdomen. The thorax of the carpenter bee (directly behind the head) is usually covered with yellow, orange, or white hairs. Female carpenter bees have solid black faces, while males have a patch of white cuticle on their face.

Habitat: Wooded areas as well as man-made structures. They do not consume wood; these bees thrive on nectar.

Nesting: Preferring a solitary life, carpenter bees live alone in the tunnels. Females chew a tunnel into the wood, with small bee-sized galleries branching from the central tunnel. Females will drive adult offspring away however it isn’t uncommon to find a young daughter sharing space with her mother.

Inside their rounded branched galleries, they form pollen/nectar loaves upon which they lay their giant eggs (up to 15 mm long). The female forms partitions between each egg cell by mixing sawdust and her saliva together. These partition walls are very similar to particle board!
Carpenter bees are long lived, up to three years and there can be one or two generations per year. Often newly hatched daughters, live together in their nest with their mother.

Biologists using observation nests or X-ray imaging techniques have observed returning foragers feeding other nest mates. These observations have led some entomologists to consider carpenter bees primitively social. However, unlike honey bees and bumble bees there are no queen or worker castes, only individual males and females. ~ US Forest Service 
Social: Groups of females may share the same area. Males and females do not share a nest.

Behavior: Carpenter bees appear clumsy, often bouncing along a wood surface. They are dazzling in mid-air, deftly weaving around obstacles and zinging after rival insects. Both sexes are mild-tempered however males are protective and will bounce against perceived threats.

The audible, low “buzz” you hear is due to powerful, vibrating thoracic muscles. Pollination is possible because of this sonication (sound “energy” is used to agitate dry pollen particles out of the flower. The pollen lands upon the bee’s body, is transported to the next flower, and then vibrated off).

Benefits: carpenter bees are generalists, content to forage wild flowers, vegetable flowers such as eggplant and tomato, and decorative garden flowers. They are most busy in the early morning although I have seen them visiting my dogwood and mimosa trees as late as dusk. They are excellent at keeping wasps at bay, given the male’s protective tendency.

Bee herding:
I have several areas where I do not want bees. The wood rails by my back door are an invitation to accidental “fly ins” whenever the door is held open for the dogs. The male bees also take issue with my coming and going. The bees are quick borers and I can’t always prevent new holes appearing. I cover the holes with wood putty. The female may be trapped inside but her death won’t harm anything.

Carpenter Bee and Passion Flower by Peter Loewer
You can hang a vertical board in your garden or erect a small, bare-wood decorative fence. This “offering” allows you to keep your pollinators happy while offering an alternative to your deck. Some people hang a simple pine board. Other makes a bee preserve, erecting a board and surrounding it with flowers. Keep in mind that the carpenter bee is too large to enter long, tubular flowers such as those found on penstemons and salvias. They use their powerful mandibles (mouth parts) to cut the corolla base and access the nectar without pollinating the flower.

Pesky males can be a deck enjoyment killer for many people. Take heart: males don’t sting. They will, however, bump against you and generally make a pest of themselves (not to mention serving as unwilling playtoys for my German Shepherd!) They are protecting their territory. You can distract them by tossing bee-sized rocks away from you; males tend to chase the rock.

Females can sting. They are generally tolerant of people and animals unless you go out of your way to handle them or are aggressive with them. People with allergies to bee venom should seek medical treatment if stung.

Gardeners usually live in harmony with these bees. You can gently push them out of the way while harvesting vegetables or tending flowers. I have noticed that they behave like honey bees when exposed to smoke; a quick exhale of cigarette smoke tends to pacify an intrepid male.

Bee prevention:
If you build it, they will come. Carpenter bees fancy wooden shutters, fence posts, door jambs, the wooden support beams under decks, wood shingles – sound wood is wood and weathered wood is downright nice. Look into coating your wood with polyurethane or oil-base paint. Carpenter bees like redwood so you may want to build using man-made materials.

A note about exterminating carpenter bees:
Pollinator decline is a serious environmental problem. Carpenter bees are an important pollinator in your garden. There are several ways to deter these bees in their quest to bore into your house, shed or deck. I personally love the appearance of natural wood decks but I also don’t mind the holes.

Having said that, there are times when the carpenter bee has overstayed its welcome. I strongly recommend that you contact a professional exterminator rather than attempting to tackle the job by yourself, especially when the nests are in locations that are difficult or dangerous to access.

"Despite its apparent lack of marquee appeal, a decline in pollinator populations is one form of global change that actually has credible potential to alter the shape and structure of terrestrial ecosystems." Entomologist May R. Berenbaum, University of Illinois

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Photographs: © 2011 T. Mininni-Totin
Lithograph: Carpenter Bee and Passion Flower Created by Peter Loewer, Asheville-Buncombe Technical Community College.
Further information: US Forest Service (http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/carpenter_bees.shtml)