Carpenter bee

Carpenter bee
Xylocopa violacea obtaining nectar
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Suborder:	Apocrita
Superfamily:	Apoidea
Family:	Apidae
Subfamily:	Xylocopinae
Tribe:	Xylocopini
Genus:	Xylocopa Latreille, 1802
Type species
Xylocopa violacea Linnaeus, 1758

Carpenter bees (the genus Xylocopa in the subfamily Xylocopinae) are large bees distributed worldwide. Some 500 species of carpenter bees are in the 31 subgenera.^[1] Their common name is because nearly all species build their nests in burrows in dead wood, bamboo, or structural timbers (except those in the subgenus Proxylocopa, which nest in the ground). Members of the related tribe Ceratinini are sometimes referred to as "small carpenter bees".

Carpenter bee finding its nectar

Etymology

The genus was described by French entomologist Pierre André Latreille in 1802. The name is derived from the Ancient Greek xylokopos/ξῦλοκὀπος "wood-cutter".^[2] Species in this enormous genus are often nearly impossible to distinguish from one another taxonomically, the majority of species being all-black, or primarily black with some yellow pubescence, differing only by subtle morphological features, and details of the male genitalia. In India, for example, any all-black species of Xylocopa is referred to by the common name bhanvra, and reports and sightings of bhanvra are commonly misattributed to a European species, Xylocopa violacea; however, this species is found only in the northern regions of Jammu and Kashmir and Punjab, and most sightings, especially elsewhere in India, refer to any of roughly 15 other common black Xylocopa species in the region, such as X. nasalis, X. tenuiscapa, or X. tranquebarorum.^[3]

Characteristics

Carpenter bees have large compound eyes.

Carpenter bees are large, sturdy, shiny, black-coloured bees, some species having yellow markings on their heads. Carpenter bees may be mistaken for bumblebees.^[4]

The marginal cell in the front wing is thin and stretched and the apex bends away from the costa. The front wing has small stigmata. The bee's labrum is concealed by the short mandibles when closed. The clypeus is flat. The thoracic menanotum is presented upright and is part of the rear surface and is almost perpendicular to the dorsal surface. The basitarsi are of the same length as the associated tibiae, and the hind pair of basitarsi is hirsute.^[4]

Ecological significance

Carpenter bee in Japan

In several species, the females live alongside their own daughters or sisters, creating a small social group. They use wood bits to form partitions between the cells in the nest. A few species bore holes in wood dwellings. Since the tunnels are near the surface, structural damage is generally minor or nonexistent.^[5]

Entrance and Brood Galleries in a Cedar Beam

Brood Galleries in a Split Piece of Lumber

Carpenter bees can be important pollinators on open-faced flowers, even obligate pollinators on some, such as the maypop (Passiflora incarnata), though many species are also known to "rob" nectar by slitting the sides of flowers with deep corollae. Xylocopa Virginica have been found to exhibit nectar robbing behavior. By piercing the corolla of long-tubed flowers, the bees are able to access the nectar without making contact with the antlers and bypass pollination. In some plants, this reduces fruit and seed production, while others have developed defense mechanisms against nectar robbing.^[6]

In the United States, two eastern species, Xylocopa virginica and X. micans, are found, and three other species are primarily western in distribution, X. varipuncta, X. tabaniformis orpifex, and X. californica. X. virginica is by far the more widely distributed species.^[7] Some are often mistaken for bumblebee species, as they can be similar in size and coloration, though most carpenter bees have a shiny abdomen, while in bumblebees the abdomen is completely covered with dense hair. Males of some species have a white or yellow face, where the females do not; males also often have much larger eyes than the females, which relates to their mating behavior. Male bees are often seen hovering near nests, and will approach nearby animals. However, males are harmless, since they do not have a stinger.^[8] Female carpenter bees are capable of stinging, but they are docile and rarely sting unless caught in the hand or otherwise directly provoked.^[7]

Many Old World carpenter bees have a special pouch-like structure on the inside of their first metasomal tergite called the acarinarium where certain mites (Dinogamasus species) reside as commensals. The exact nature of the relationship is not fully understood, though in other bees that carry mites, they are beneficial, feeding either on fungi in the nest, or on other harmful mites.

Behavior

Carpenter bee nest in a tree trunk

A male X. caffra carpenter bee, feeding from flower, South Africa

X. virginica in Indianapolis

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^[9] and Xylocopa nasalis^[10]. 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.^[9]

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.^[9] Xylocopa pubescens is one carpenter bee species that can have both social and solitary nests.^[11]

Carpenter bees make nests by tunneling into wood, vibrating their bodies as they rasp their mandibles against the wood, each nest having a single entrance which may have many adjacent tunnels. 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.^[12]

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.^[13]

Natural predators

Woodpeckers eat carpenter bees, as do various species of birds, such as shrikes and bee-eaters. So do 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.^[14]

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

Gallery

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  Carpenter bee

Species

X. cubaecola in Guantanamo; endemic to Cuba

X. violacea in Sardinia, Italy

X. waterhousei female

References

External links

Wikimedia Commons has media related to Xylocopa.

Wikispecies has information related to: Xylocopa

• United States Xylocopa Identification Guide
• List of Species
• Worldwide Species Map
• Close-up photos of a carpenter bee – taken near the town of Chavarillo, Veracruz, Mexico
• Carpenter bees, Xylocopa spp. on the UF / IFAS Featured Creatures Web site