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Carpenter bees are species in the genus Xylocopa of the subfamily Xylocopinae. The genus includes some 500 bees in 31 subgenera. The common name "carpenter bee" derives from their nesting behavior; nearly all species burrow into hard plant material such as dead wood or bamboo. The main exceptions are species in the subgenus Proxylocopa, which dig nesting tunnels in suitable soil.
Many species in this enormous genus are difficult to tell apart; most species are all black, or primarily black with some yellow or white pubescence. Some differ only in subtle morphological features, such as details of the male genitalia. Males of some species differ confusingly from the females, being covered in greenish-yellow fur. The confusion of species arises particularly in the common names; in India, for example, the common name for any all-black species of Xylocopa is bhanvra (or bhomora - ভোমোৰা - in Assamese), and reports and sightings of bhanvra or bhomora 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 reports of bhanvra, 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.
Non-professionals commonly confuse carpenter bees with bumblebees; the simplest rule of thumb for telling them apart is that most carpenter bees have a shiny abdomen, whereas bumblebee abdomens are completely covered with dense hair. Males of some species of carpenter bees have a white or yellow face, unlike bumblebees, while females lack the bare corbicula of bumblebees; the hind leg is entirely hairy.
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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 superficial. However, carpenter bee nests are attractive to woodpeckers, which may do further damage by drilling into the wood to feed on the bees or larvae.
Carpenter bees have short mouthparts and are important pollinators on some open-faced or shallow flowers; for some they even are obligate pollinators, for example the maypop (Passiflora incarnata) and Orphium, which are not pollinated by any other insects. They also are important pollinators of flowers with various forms of lids, such as Salvia species and some members of the Fabaceae. However many carpenter bees "rob" nectar by slitting the sides of flowers with deep corollae.
Xylocopa virginica is one example of a species with such nectar robbing behavior. With their short labia the bees cannot reach the nectar without piercing the long-tubed flowers; they miss contact with the anthers and perform no pollination. In some plants, this reduces fruit and seed production, while others have developed defence mechanisms against nectar robbing. When foraging for pollen from some species with tubular flowers however, the same species of carpenter bees still achieve pollination, if the anthers and stigmata are exposed together.
