In praise of carpenter bees.
When we were buying our first home, the inspector noted that the ornamental trellis above the back patio was home to several carpenter bees. My immediate fear was this was going to increase the value of the house beyond what we could afford. I knew how much entertainment these harmless acrobats can provide and they were not listed as one of the amenities that came with the sale. Almost 10 years later, our carpenter bee population has steadily grown. The trellis has more holes in it, but it’s basically doing fine. Best of all, we have never been given a bill for all of the pollination and amusement our carpenter bees have provided for us.
Carpenter bees are closely related to honey bees and bumble bees. However, instead of building hives with a single queen bee and lots of sterile female “worker bees," carpenter bees are not as socially inclined. Unlike honey bees and bumble bees, each female carpenter bee is capable of raising her own family. Here in Pennsylvania, by far the most common of our two species of carpenter bee is Xylocopa virginica. They look like huge black bumblebees and have a shiny black abdomen. The females are capable of stinging, but you would have to work really, really hard to get stung. She will never come after you. Male carpenter bees are less shy around people, partly because they are so focused in protecting their “turf” (and local females) from other male bees. It is very common to see male carpenter bees having aerial “dogfights.” You can easily recognize male carpenter bees by their bright yellow faces. You will never be stung by a male bee (or wasp), since the males do not have stingers.
Female carpenter bees make new nests by tunneling into wood. They drill their perfectly round 3/8 inch diameter holes by vibrating their strong flight muscles, and slowly turning their bodies around and around. Their sharp teeth do the drilling, much like a woodworking router. No chewing required! If you look under one of their holes, you might find a pile of sawdust. This is because they do not eat the wood like termites do. The females spend the early summer bringing lots of pollen and nectar to their holes and forming it into little balls, called “bee bread.” This ball of pollen provides a single growing larva with all of the food it needs to grow to adulthood. A female carpenter bee will have about 4-6 larvae, which really isn’t very many for an insect.
The life cycle of carpenter bee starts in the late spring when females lay eggs on the balls of bee bread they busily prepared. During the early part of the summer, the eggs will hatch and the larvae will feed until they become pupae. A few weeks later, a new generation of adults will emerge from their wood holes. Around mid-late summer, the new adults explore the world around them and feed themselves with pollen and nectar (doing some more pollination work). They don’t go very far away from their original holes. If possible, they like to hibernate for the winter in the same holes they were born in. Early in the spring next year, they will crawl out of their holes, ready for action. This is why on one of the very first really warm days of spring, you will be likely to see lots of carpenter bees buzzing around.
Insecticides and carpenter bees
I know that carpenter bees are a common homeowner complaint. Some people find them a bit scary, which us understandable, especially if they have not been properly introduced to each other. Hopefully, the knowledge that they are not aggressive or dangerous will help more people learn to live with them. Other people are legitimately concerned about the structural damage that can be done to exterior wood on their homes. In these cases, professional assistance may be warranted. If you must remove your carpenter bees, I would definitely recommend against the “do it yourself” approach with household insecticides. In addition to the obvious risks of using toxic chemicals, this can even make your carpenter bee problems worse, as the bees may look for new and even less appropriate places to employ their handiwork.
With ice cream toppings, “more is better.” This rule does NOT apply to insecticides! Even when following the instructions, people routinely use insecticides in their gardens at levels that are vastly greater than would be allowable in agriculture! Of particular concern is a new class of “eco-friendly” insecticides that are available at most home and garden stores. They are called neonicotinoids but are listed on the label with a variety of unpronounceable names (e.g. imidocoloprid). If you can’t tell if a product contains neonicotinoids, ask the store manager to help you figure it out, or try calling the phone number on the package.
Neonicotinoids are less toxic to humans than many of the “old fashioned” insecticides you might have used in the past. They are artificially synthesized chemical mimics of nicotine, a natural insecticide found in tobacco. Neonicotinoids are taken up into plant fluids including nectar, making the plant itself toxic to insects that feed on them. So far so good, what’s the problem? Unfortunately, they can build up to alarmingly high concentrations in the flowers of some ornamental shrubs and trees. In this way, they can be found in plant nectar in high doses that have proven to be lethal to many pollinators. Some scientists are pinning the blame on these commonly used insecticides for all of the troubles that honeybees have been experiencing (such as colony collapse disorder). This is still an active area of research, and the jury is still out. Meanwhile, solid research into the environmental effects of neonicotinoids used in the home & garden setting is urgently needed. To what extent are they disrupting the lives of honeybees, native bees and other pollinator insects such as butterflies?
If you are at all inclined to use insecticides in your backyard (after consulting with the fireflies, bees and butterflies who will also be affected), please read this article before heading off to the local hardware store.
If do not have carpenter bees and want them, or you would like to encourage your carpenter bees to nest a little further away from your house, I would suggest putting some weathered, unpainted lumber (like untreated 2X4s) out for them to use as a home. Place it as near or far away from your house as you please. For a few dollars and a couple of nails, you can gradually increase the aesthetic and ecological value of your property by building a population of friendly and helpful carpenter bees.