Carpenter bee
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| Carpenter bee (Xylocopa virginica) on Redbud (Cercis canadensis) | |
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| Subfamily: | Xylocopinae
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Many | |
Carpenter bees (Xylocopinae subfamily) are important pollinators, especially of open-faced flowers, though the larger species are also known to "rob" nectar by boring holes in the sides of flowers with deep corollas (thus not accomplishing pollination). The smaller species tunnel into pithy stems to build their nests. Some of the larger species bore holes in wood dwellings and can become minor pests.
Appearance
In the U.S. the common eastern carpenter bee, Xylocopa virginica, is the one most encountered by humans. It is often mistaken for the larger bumblebee species. They are similar in size and coloring. The primary physical difference is on the abdomen. Carpenter bees have a shiny black abdomen. Bumblebees have a fuzzy abdomen with some yellow coloring. The eastern carpenter bee also has a much larger head than bumblebees. Most other species of carpenter bees are smaller and nest primarily in the wild. Eastern Carpenter bee's are as well, extremely easy to sex at a glance. Males half a yellowish to white dot on their forehead, as opposed to females who are just black colored. This is a good indication as to if they will be able to sting or not if somehow provoked.
Nesting
Carpenter bees make nests by tunneling into wood. They make an initial upward hole in an overhang. Then, they make many horizontal tunnels. Unlike termites, carpenter bees (also called woodcutters) do not eat wood. They discard the bits of wood. The tunnel functions as a nursery for brood and the pollen/nectar upon which the brood subsists.
Because of their pollination skill, some people allow carpenter bees to stay around the home in the early spring, living with the cosmetic damage, or repairing the damage later. In some areas carpenter bee populations are supported for fruit pollination, by supplying them with suitable blocks or boards of soft wood.
In the eastern U.S., Xylocopa virginica overwinter as adults inside the same tunnels where they hatched that summer. In spring, they awaken. (This pattern may be different with other species or other climates.) The males hover around looking for mates. The female enlarges the existing tunnel, or moves nearby and bores a new tunnel. She creates separate partitions in the tunnel out of sawdust and saliva. She provisions each section with a pastelike wad of pollen and nectar as food for the larva, lays one egg on it, and seals it off. In late summer, the newly hatched adults break through the partitions to escape to the outside world.
Rarely, active nests in a home can involve considerable damage, but woodpeckers normally are the primary cause of it, as they search out larval bees.
Carpenter bee nests are rather easy to spot. They bore a highly polished hole directly up into the bottom of an overhang. The entrance hole is about 11 millimeters in diameter. When the female is boring tunnels, there is a collection of fresh sawdust below the hole and the sound of boring can be easily heard.
Deterrence
Because pollinator decline is a serious environmental issue, and carpenter bees are increasingly important pollinators, carpenter bees should not be killed.
To deter carpenter bees from making nests in valuable wood, it can be kept painted or stained. Paint is a better deterrent than stain, but bare wood is very inviting to a bee looking for a place to start a new nest. In unusual cases where carpenter bees persist in spite of paint, the edge of the wood can be covered with a narrow strip of flashing or screening, and painted, thus providing a physical barrier.
Since previous nests are the primary nests each year, blocking or poisoning nests can often backfire on the homeowner, by encouraging the carpenter bee to bore new nests. Over time the borrowing of these new holes may weaken structurs.
An alternative means of preventing nesting in valuable wood is to attract the bees to another location by propping a beam of attractive bare wood where you would prefer the bees to stay. The theory is that the bees will build their nests in the wood you supply for them and stay away from your house. Often, an old wooden shed or barn sustains a population of carpenter bees.
Behavior
Carpenter bees are solitary bees, not making social nests. However they tend to be gregarious, and often several will nest near each other.
Male eastern carpenter bees are curious and will investigate anyone, including humans, that comes near their nests. The curiosity is often interpreted as aggressiveness, however, the males are only aggressive to other male carpenter bees. They do not have stingers and cannot cause any real harm. The female carpenter bees tend to be busy with floral visitation and nest provisioning, but have the ability to cause a painful sting if captured.
Males spend many hours guarding their territory against other male bees, hovering about the nests for hours on sunny days. They sometimes attempt to mate with other insects or small birds.
An Interesting trick to use to "move" a male carpenter bee out of the way is to pick up a small pebble (roughly the size of the bee), then toss it by the bee. They will atempt to attack it, distracting them for a few moments, long enough for a human to get by.