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Carpenter Bees

Carpenter bees are traditionally considered solitary bees, though some species have simple social nests in which mothers and daughters may cohabit. Examples of this type of social nesting can be seen in the species Xylocopa sulcatipes and Xylocopa nasalis. When females cohabit, a division of labor between them occurs sometimes. In this type of nesting, multiple females either share in the foraging and nest laying, or one female does all the foraging and nest laying, while the other females guard.

Solitary species differ from social species. Solitary bees tend to be gregarious and often several nests of solitary bees are near each other. In solitary nesting, the founding bee forages, builds cells, lays the eggs, and guards. Normally, only one generation of bees live in the nest. Xylocopa pubescens is one carpenter bee species that can have both social and solitary nests.

Carpenter bees make nests by tunneling into wood, bamboo, and similar hard plant material such as peduncles, usually dead. They vibrate their bodies as they rasp their mandibles against hard wood, each nest having a single entrance which may have many adjacent tunnels. As a subfamily, they attack a wide range of host plants, but any one species may show definite adaptations or preferences for particular groups of plants. The entrance is often a perfectly circular hole measuring about 16 mm (0.63 in) on the underside of a beam, bench, or tree limb. Carpenter bees do not eat wood. They discard the bits of wood, or reuse particles to build partitions between cells. The tunnel functions as a nursery for brood and storage for the pollen/nectar upon which the brood subsists. The provision masses of some species are among the most complex in shape of any group of bees; whereas most bees fill their brood cells with a soupy mass and others form simple spheroidal pollen masses, Xylocopa species form elongated and carefully sculpted masses that have several projections which keep the bulk of the mass from coming into contact with the cell walls, sometimes resembling an irregular caltrop. The eggs are very large relative to the size of the female, and are some of the largest eggs among all insects.

Two very different mating systems appear to be common in carpenter bees, and often this can be determined simply by examining specimens of the males of any given species. Species in which the males have large eyes are characterized by a mating system where the males either search for females by patrolling, or by hovering and waiting for passing females, which they then pursue. In the other mating system, the males often have very small heads, but a large, hypertrophied glandular reservoir is in the mesosoma, which releases pheromones into the airstream behind the male while it flies or hovers. The pheromone advertises the presence of the male to females.

Male bees often are seen hovering near nests, and will approach nearby animals. However, males are harmless, since they do not have a stinger. Female carpenter bees are capable of stinging, but they are docile and rarely sting unless caught in the hand or otherwise directly provoked.

Natural predators

Woodpeckers eat carpenter bees, as do various species of birds, such as shrikes and bee-eaters as well as some mammals such as ratels. Other predators include large species of Mantodea and predatory flies, particularly large species of the family Asilidae. Woodpeckers are attracted to the noise of the bee larvae and drill holes along the tunnels to feed on them.

Apart from outright predators, parasitoidal species of bee flies (e.g. Xenox) lay eggs in the entrance to the bee’s nest and the fly maggots live off the bee larvae.