Sunday, June 23, 2024

An eastern carpenter bee flies in Powder House Square in Somerville on May 22, 2022. (Photo: Jeanine Farley)

One of the first bees I see every spring is a carpenter bee buzzing around the blossoms of my crabapple tree. Carpenter bees are large (about three-fourths of an inch) and look similar to bumblebees. You can tell the difference because carpenter bees have a shiny hind section (abdomen); bumblebees have hairy abdomens, often with yellow markings and are not shiny.

Some bees, including honeybees, are social. They live in colonies and divide up the jobs that must be done. Some bees are solitary, and one female bee does all the work – she makes a nest, provisions it with food and lays eggs that will become the next generation. Most carpenter bees are solitary. One, the eastern carpenter bee (Xylocopa virginica), is neither solitary nor social, but somewhere in between.

An eastern carpenter bee in Groton on Aug, 12. (Photo: Tom Murray)

Some scientists think this bee is evolving from being a solitary bee to a social bee.

Carpenter bees get their name because the female bee excavates tunnels in wood where she lays her eggs. Contrary to popular belief, carpenter bees do not eat wood. They feed on pollen and nectar like other bees; therefore, they are important plant pollinators.

An eastern carpenter bee in Groton on May 3. (Photo: Tom Murray)

Adult carpenter bees first emerge in April and May after overwintering in a tunnel. Males and females mate and the females begin preparing a tunnel for a nest. They consume nectar for energy. Because it is a lot of work to build a tunnel a female prefers to rehab an old one – lengthening or remodeling it as needed – rather than start anew.

To excavate a tunnel, the female uses her jaws (mandibles) to cut a hole about the diameter of her body (one-half inch). She bores into the wood for about an inch, then turns at a right angle and excavates along the grain for 6 or more inches. A female carpenter bee can excavate about an inch per week.

An eastern carpenter bee in the Tufts Community Garden in Medford on Aug. 22. (Photo: Jeanine Farley)

While the female is building, the male hovers around the area to keep intruders away. You might spot him darting after an insect that flies too close. Some people are afraid of carpenter bees at this time because the male buzzes loudly and hovers around people who approach the nesting site. But male bees do not have stingers; their goal is simply to encourage you to leave. Female carpenter bees, on the other hand, have stingers, but they are docile and want to build their nest in peace. They do not want to get in a fight, which they might lose. Their goal is to live long enough to provision their nest. They will only sting if you pick them up or harm them.

Because male bees are busy guarding their territory by day, they do most of their foraging and resting at night. During the day, they take small breaks, but after these breaks, they often have to fight off intruding insects. By late spring, the males die.

An eastern carpenter bee near Powder House Boulevard in Somerville on Aug. 24. (Photo: Jeanine Farley)

Once the tunnel is complete, the female is almost ready to lay her eggs. First she makes bee bread – a ball of pollen and regurgitated nectar. She puts it at the end of the tunnel, lays an egg on top of it and walls off the bee bread with a plug of chewed wood. This forms a 1-inch cell in which the egg can mature. She repeats this process, filling the tunnel with a row of six to eight cells with bee bread and one egg inside.

When the eggs hatch in early summer, the larvae feed on the bee bread in their cells. After about seven weeks, a larva has fattened up; it weaves a cocoon around itself and undergoes metamorphosis into an adult bee. The new adult remains in its cell for several additional weeks. In late August, it chews through the cell wall and ventures out of the tunnel. The bee at the farthest end of the tunnel is the oldest and hatches first. It chews through several cell walls and may climb over its younger siblings. Soon, all the bees hatch and leave the tunnel.

An eastern carpenter bee flies between flowers in East Boston on Aug. 12. (Photo: Jeanine Farley)

Once out of the tunnel, the young adults collect pollen from flowers. They store the pollen in the tunnel in which they grew up. As winter approaches and temperatures drop, the bees hibernate there. In the spring, they reemerge, mate and begin the cycle all over again. For most, this is the last time they will overwinter.

Eastern carpenter bees (Xylocopa virginica) are a little different. They are not always completely solitary. Sometimes a female bee who has overwintered twice will nest with one to four other females. This 2-year-old dominate, or primary, female lays all the eggs and does most of the work. Secondaries wait, ready to take over if something happens to the primary. They may collect some food for the larvae or help maintain the nest. Tertiary females have overwintered once. They do not leave the nest to forage but rather guard the entrance to the nest. They rely on food provided by the other females. After tertiary females overwinter a second time, they may become primary females. Even though several females may work together, they do not produce more offspring than one solitary carpenter bee.

Carpenter bees like to nest in wood they can tunnel through easily – that is, soft wood with a straight grain. You might find them nesting in fence posts, firewood, porches, shutters or other weathered wood. They avoid wood that is painted or covered with bark. Most carpenter bee damage is minor. Sometimes woodpeckers search for overwintering bees by riddling their tunnel with holes.

Because carpenter bees spend much of their lives in their tunnels, you see them most often in the spring and early summer or in the late summer. Enjoy watching their hovering antics, and remember they are docile and mean you no harm.


Reader photo

Nancy Nordin spotted this raven in Tisbury on Jan. 1.


Have you taken photos of our urban wild things? Send your images to Cambridge Day and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.

Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.