The genus Xylocopa are the large carpenter bees, a group distributed worldwide but more prevalent in warmer regions. They are all generally large, mainly black bees, which may be mistaken for bumblebees, but are generally larger and comparatively hairless (this is why the abdomen appears shiny and hard).
They range from around 14 mm to 35 mm in body length. Many species are sexually dimorphic, meaning the males and females look distincly different. Females of some species are mainly black, while the males are hairier overall and mainly yellowish. In other species, males are all-black like females, but have a distinct yellow patch on the front of the head (the "face"). However, in some species, such as the large Xylocopa latipes, there is no difference in colour, and only such features as the eyes and abdomen, when examined closely, are useful for distinguishing the sexes.
True to their name, carpenter bees generally nest in wood. Some species are quite specialized in this aspect. For instance, species of the subgenus Biluna (bamboo carpenter bees), of which at least two species are common in Hong Kong, only nests in dead bamboo stems. They make their characteristic entrance hole, round in shape and approximately 1cm in diameter, in the side of the bamboo stem. Since bamboo poles are commonly used in scaffolding and to support plants in Asian countries, this bee can be found even in Hong Kong's urban estates.
Other species, however, are apparently not fussy in their choice of nesting sites, and will often nest in wooden structures around homes. They can sometimes be pests when they burrow into wood, causing some damage in the process. However, the damage caused by these bees is not as great compared to that caused by termites, for example.
The photo above shows a typical entrance hole of a carpenter bee's nest. In this case, the nest of Xylocopa aestuans was built in a solid wooden pole. The female had just returned from foraging, as is evident by the pollen on her abdomen. However, she assumed a defensive pose due to the disturbance when I accidentally hit the pole. She guards the hole with her abdomen; if the hole is touched, she will sting.
Carpenter bees often cause fear in many, due to their large size, intimidating appearance and loud buzzing. However, they are completely harmless. A sting from one of these giant bees is a lot less painful than one would expect, although it does cause some swelling. Furthermore, these bees never attack, so the only way one may be accidentally stung would be to actually crush one or to unknowingly touch the entrance hole.