Carpenter bees get their common name from their habit of boring into wood to make galleries for the rearing of young. These are worldwide in distribution with 7 species occurring in the United States.

The adult body length is about 1/2-1" (12.5-25 mm); robust in form, resembling bumble bees, but with top surface of abdomen largely bare and shining. Hind tibiae with apical spurs. Front wing 2nd submarginal cell triangular; hind wing with a small jugal lobe (lobe on rear margin near body). Similar groups include: (1) Bumble bees (Apidae) have hairy abdomen with yellow markings, 2nd submarginal cell somewhat rectangular to pentagonal, and hind wings lack a jugal lobe. (2) Some robber flies (Diptera: Asilidae) which resemble bumble bees, with only 1 pair of wings. (3) Some hawk moths (Lepidoptera: Sphingidae) which resemble bumble bees, with siphoning mouthparts.

The representative species include the following:
1. The carpenter bee, X. virginica (Linnaeus), is the most common eastern species and its range extends westward to Kansas and Texas. It is about 1" (25 mm) long and closely resembles the bumble bee except that the abdomen is black and shiny instead of at least partially covered with yellow hairs. The male has a yellow face, whereas, the female's is black.

2. The California carpenter bee, X. californica (Cresson), is found in the north Coast Ranges and the Sierra Nevada of California and in Oregon's Cascade Mountains. This bee is 3/4-1" (20-25 mm) long and both sexes can be mostly metallic green or blue with grayish/dusky wings. The male's pronotum has orange, yellow, or white hairs and its 1st abdominal segment has whitish hairs.

3. The valley carpenter bee, X. varipuncta (Patton), is found primarily in the valleys and lower foothills of California and Arizona. This species is about 3/4" (18-20 mm) long. The female is shiny black with brilliant metallic purple, brassy, or bronzy reflections, in stark contrast to the golden brown or buff color of the male. The female's wings are somewhat smoky.

4. The mountain carpenter bee, X. tabaniformis (Smith), is found mostly in the foothills and mountains of Arizona, California, Nevada, and Oregon. This bee is about 1/2-5/8" (12-17 mm) long and both sexes are black. The male's head has yellow and white hairs mixed with black hairs.

Carpenter bees are not social insects and do not live in nests or colonies. The adults overwinter, typically in abandoned nest tunnels. In the spring, the survivors emerge and feed on nectar. Then mating begins and extends into nest-construction time. The mated female may either reuse an old gallery, construct a new one by lengthening an old gallery, bore an entirely new one, or extend a gallery from a common entrance hole. The female typically bores a circular hole (same diameter as her body) straight into the wood across the wood grain for a distance equal to her body length. Then the gallery takes a right-angle turn, usually with the grain of the wood and parallel to the outer longitudinal surfaces. New galleries average 4-6" (10-15 cm) long but galleries developed/used by several bees may extend up to 10 feet (3 m).

The female provisions each gallery cell starting at the closed end of the gallery with a mass of pollen and regurgitated nectar upon which she lays a single egg. This portion of the gallery is then sealed off with a chewed wood-pulp plug, making a chamber or cell. This process is repeated until a linear series of 5-6 cells is completed, about 1 cell per day. Developmental time (egg to adult) for the carpenter bee (X. virginica) is about 36 days and for the mountain carpenter bee (X. tabaniformis), it is about 84-99 days.

Females of the carpenter bee (X. virginica) will nest in a wide range of woods, but prefer weathered and unpainted wood. Valley carpenter bees prefer partially decayed live oak, deciduous oak, eucalyptus, and other hardwoods. The California carpenter bee nests in incense cedar and redwoods. The Mountain carpenter bee is recorded as nesting in structural timbers.

Male carpenter bees tend to be territorial and often become aggressive when humans approach, sometimes hovering a short distance in front of the face or buzzing one's head. Since males have no stinger, these actions are merely show. However, the female does have a potent sting which is rarely used.

Information compiled from the National Pest Management Association, Inc. (NPMA)