Like solitary wasps, and unlike social bees and wasps, solitary bees do not form colonies or work together. Therefore, they are far less of a threat than their social relatives.
Unlike the wasps, bees are completely herbivorous. Adult bees need only nectar to survive, while the larvae are fed on a mix of nectar and pollen collected by the female.
There are several important groups of solitary bees, all with different nesting habits. Most bees have a "pollen basket" or "pollen brush" (long hairs intended to trap and collect pollen) on their bodies, on which they accumulate pollen from every flower they visit. The location of this on the bee's body also varies between families.
The Anthoporidae is a large family of bees, mostly stout and robust in build. Within this family, the sub-family Anthoporinae are small to medium-sized, stout bees covered with dense hairs. They generally fly fast and can hover; they also have very long tongues in general, and are able to reach into deeper flowers. Many member of this group nest in burrows dug in the ground.
Within this sub-family, a group known as the blue-banded bees, members of the genus Amegilla, are common and widely distributed throughout the Asia-Pacific region, from Taiwan and Northern China all the way down to Australia. There are several similar species in this genus, but all are small to medium (7 to 15mm average), with conspicuous pale blue, bright blue or blue-green bands on a mainly black abdomen. These bees are beautiful when viewed up close but often fly too fast to be seen clearly; it is only when they hover or enter a flower that the blue can be seen clearly.
Another sub-family of the Anthoporidae is the Xylocopinae. These are commonly known as the carpenter bees, and there are several groups, varying greatly in size and appearance. At one end of the scale are the small or dwarf carpenter bees, genus Ceratina. These are small bees of mere millimetres in length, often metalliic green or blue, or marked with yellow streaks, although they are often so small that it takes a close look to get a good view of the colour and patterns. These bees build their nests by biting into dead or dying stems of shrubs.
At the other end of the scale are the large carpenter bees, genus Xylocopa. These range from large to very large, and are generally shiny, with a relatively hairless abdomen. A common species in much of Europe is Xylocopa violacea, a fair-sized type, all black, with a brilliant bluish-purple sheen on the wings. However, some Asian species get even larger. Xylocopa latipes is probably one of the biggest, and also one of the biggest bees in the world! It consistently reaches or even exceeds 34mm, and is fully black. Many of these bees are sexually dimorphic, that is, it is easy to distinguish between males and females. In many of these species, females are fully black, or black with yellow on the body, while males are fully yellow or have much more yellow than females. Some males, though all black like the females, have a whitish or yellow patch on the front of the head.
The carpenter bees are so named due to their nesting habits; they bite into wooden surfaces such as logs and tree branches, and, in urban area, wood used for construction. The nest entrance is a round hole, roughly 1cm or so in diameter. Despite their large size and intimidating appearance, these bees are virtually harmless. Their sting is surprisingly mild for their size. Also, males frequently hover in their territory and make darts at any moving object in the vicinity, but are harmless, since they can't sting. The females never attack. In fact, if the nest site is disturbed, the bees do not emerge; they hide in the nest, with a female guarding the entrance by blocking it with her abdomen. If the hole is touched, she will sting.
Another notable group is the family Megachiliidae, frequently known as the leafcutter bees. These bees are distinct because they cut small circular sections out of leaves, which they use to line their nests. These bees have varying nesting habits as well; some nest simply in existing crevices, while some make nests of mud, in a similar fashion to the mud-dauber and potter wasps. A couple of species even use snail shells exclusively as nesting sites! The pollen brush on leafcutter bees is under the abdomen; a whole mat of dense, light-coloured hairs is quite noticeable, and often the bee can be seen with a full load of pollen under its abdomen. Most of these bees are quite small and vary in colour, usually being a combination of black, gray, yellow, orange or white. They are all similar in shape and easy to identify as Megachiliid bees, but sometimes species identification is a task for the expert.
Although most Megachiliid bees are quite small, a species known as Megachile pluto (Wallace’s giant mason bee) is in fact the longest bee known. Females reach 38mm and have unusually large heads and mandibles. This rare species is found only in Bacan, an island in the northern Moluccas in Indonesia. It is also unique in that it nests in termite nests!
However, the bulk, width wingspan and other measurements (except the head) of Xylocopa latipes (arguably the largest of its group) distinctly exceed that of Megachile pluto. Furthermore, at 35mm, the carpenter bee is only slightly shorter than the Megachiliid. The illustration above clearly shows the comparison. The length of the Megachile pluto has been pumped up to 40mm; this shows that even a specimen of larger than known size still falls short of the bulk of big Xylocopa. The information and illustration was kindly provided by and copyright of David Williams.
Another unusual group is the Halictidae, which are mostly small, sometimes brightly coloured bees; many are bright green or have green, blue and orange stripes. Known as sweat bees, some members of this group actually approach sweating humans in an attempt to replenish lost body salts!
This is only a quick overview of the various solitary bees. The variety of these seems infinite!