The Valley Carpenter Bee (Xylocopa varipunctata) is the largest species of bee in California, and they are not messing around. They are huge! The females, which are completely black and very dramatic looking, can get up to just over an inch long, and the
males, which are yellow with green eyes, are only slightly smaller!
Carpenter Bees are in the genus Xylocopa, the large carpenter bees. There are about 500 species in this genus, worldwide. Five of these species are found in North America and three of them are found in California. Xylocopa comes from the Greek word xylokopos which means ‘wood-cutter,’ a reference to the nesting behavior of these species. The Valley Carpenter Bee is named after the California Central Valley where it is found.
Carpenter Bees have some pretty fascinating behaviors. Generally, they are solitary bees. The females make their nests by boring holes in wood, usually the undersides of branches or beams. They carve their nests by rasping their mandibles against the surface of the wood and vibrating their wings. The holes they bore are not very deep, and so structural damage in not really a concern. However, they are not strictly solitary. Mothers and daughters, or sisters, will sometimes share the same nest. Sometimes they will even divide labor by having one female primarily guard the nest and the other primarily searching for food. Even unrelated females are often quite gregarious, and will often be found nesting in the same general area.
The males generally adopt one of two mating behaviors, and it is easy to tell which species use which strategy by the size of their eyes. Males of some species have very small eyes. These males release large amounts of pheromones that the females use to locate the male. The males of other species have very large eyes. These males search for nest holes of females, and hover outside them waiting for the females to fly by as they are coming or going, and then follow them and try to mate. The male Valley Carpenter Bees that you might see zooming around the Sacramento area have very large green eyes, so they must use the search and follow strategy.
As with so many other bee species, Valley Carpenter Bees pollinate many flowers, but sometimes they get a bit greedy. If they find a flower that is too deep for them to reach the nectar from the inside of the flower, and so pollinate it in the process, they sometimes use their strong mandibles to slit the side of the flower near the base of the petals from the outside and steal the nectar!
If you get to see a Valley Carpenter Bee, they may approach you. Don’t be alarmed. These bees often approach other animals, but both sexes are very docile and the males don’t have stingers at all. So enjoy the visit with these magnificent creatures!