As spring brings warmer temperatures and the dormant world begins to wake, we’re seeing all sorts of plant an animal activity in our yards. If you’re one of the many homeowners noticing small sawdust piles appearing on your wooden porch or around your home, take note as this is a sure sign that you have carpenter bees excavating tunnels, which serve as sites for egg laying and larval development.
Traps, treated wood and pesticides may be employed to defend wooden surfaces, but entomologists also explain that these bees serve important roles as pollinators in Georgia’s landscape. But, before we jump into ecology and control options, let’s first sort out how to properly identify these insects.
As with many bees, carpenter bees (Xylocopa virginica) are yellow and black and while they may resemble the beloved bumblebee, there are some distinct differences between the two. Typically, carpenter bees are about an inch long. They have a black abdomen and have areas of yellow hair on their thorax. A white spot on the front of their face is characteristic of adult males. Female carpenter bees can inflict a painful sting, but rarely do. Although males cannot sting, they will hover in an effort to frighten adversaries.
One easy way to remember how to distinguish between the two species is to remember that unlike the bumble bee, carpenter bees lack the fuzzy-looking hairs on their abdomen. Whenever I’m teaching eager youngsters about basic entomology, we remind them that “carpenter bees have a shiny hiney.” While the phrase may lack scientific gravitas, it seems to do the trick every time!
Adult carpenter bees only live a few weeks, but during that short time they drill through wood to lay their eggs. Bare, unpainted or weathered softwoods like redwood, cedar, cypress and pine are preferred. Painted or pressure-treated wood are reported to be less vulnerable, but personal experience suggests that paint alone offers little protection. Railings, porch ceilings, windowsills, door frames, headers, rafters and even siding are often subject to attack.
Carpenter bee holes and tunnels are perfectly round and about the diameter of a finger. Coarse sawdust beneath an entry hole and burrowing sounds are often the first signs of the bees. They drill approximately an inch into the wood and then tunnel along with the grain. Since they often reuse the same spots, holes and tunnels may reach several feet in length. As one can imagine, these insects can do severe damage over the long term. Each generation carves nest partitions by chewing the insides of the tunnel and making a paste to create their nest. Carpenter bees overwinter as adults in abandoned nest tunnels and emerge in the spring. After mating, female bees drill holes in wood and lay eggs within a series of small cells. A ball of pollen is added providing food for larvae until they emerge as adults in late summer.
So, what can be done? Painting wood is suggested as a preventative control method, but while several coats of an oil-based or polyurethane paint may discourage the bees, it won’t make the wood completely bee-proof. Spraying adults with aerosol insecticides will kill them, but just spraying wood surfaces will not. Insecticides, such as carbaryl or deltramethrin dusts labeled for carpenter bee control, must be injected into each tunnel in order to be effective.
If chemical control is an option you wish to take, keep in mind that spraying for carpenter bees at night may be more effective because the adults may not be near the nest during the day. Leave the hole open for a few days after treatment to allow the bees to come in contact with and distribute the insecticide throughout the nest galleries. The next step is plugging the holes with a wooden dowel, then applying caulk or wood putty when there is no longer evidence of bee activity. If activity continues, additional residual insecticide application should be made at weekly or twice weekly intervals.
A secondary result of carpenter bees may be damage from woodpeckers. Large and noisy, carpenter bee larvae often attract woodpeckers who are looking for a tasty snack. Unfortunately, woodpeckers can cause further damage when they hunt for carpenter bee larva. If woodpeckers explore the eaves of your home, they are more than likely in search of the carpenter bee larva.
Having said all of this, despite their destructive potential, carpenter bees have good pollinating qualities. After the female carpenter bee leaves a tunnel, she visits flowers and gathers pollen for her eggs. Visits from flower to flower transfers pollen resulting in successful fruit formation. Without insect pollination, many plants will produce little fruit.
It is reasonable to protect home structure from damage, but use insecticides carefully, following label directions exactly. Confining your control measures to only where they are needed and effective will protect against unnecessary pollinator mortality.
Looking for more tips on the management of pest insects in and around the home? Ask your Extension office about the UGA Extension Bulletin #1412.