Tuesday, October 21, 2014

Carpenter Bees

Carpenter Bee nectaring on Goldenrod

    Eastern Carpenter Bees (Xylocopa virginica) are not always well liked by people. First of all due to their large and intimidating appearance, and secondly due to the perceived damage they can cause wood. They look like very large bumble bees, but are not only larger, but also have bulkier heads and little to no "hair" on their abdomens. This often gives them a shiny, blue-black appearance unlike the hairy look of the smaller bumble bees.

Bumble Bee (left) and male Carpenter Bee (right) on Goldenrod

     Despite their large size, these are fairly docile creatures, very rarely stinging. The males can be told apart from females due to the white patch on their face and are the ones who likely make these bees look intimidating. They stake out a territory near wood structures that females are tunneling into. They then patrol, challenging anything that comes into their little area. Being somewhat short sighted,  they sometimes get uncomfortably close checking out who has entered their territory. They are completely harmless however, doubly so since only female bees/wasps can sting any ways. Stingers are modified ovipositors (egg-layers) so males do not have any way to sting.

Inside look at a Carpenter Bee hole

     Carpenter bees are solitary, unlike bumble bees, with a single mother building, tending, and occupying a tunnel with her young. She chews a hole into old wood and then angles off to one side where she builds separate cells for each of her young. She collects pollen/nectar to provision the chamber (cell) and then seals it off with saw dust from the next cell. You can often tell an active hole by the saw dust underneath.  Xylocopa eggs are among the largest of bee eggs, among the largest of most insects. They can measure almost half the bee's abdomen. Only a few eggs are laid by each mother each summer, often 8 or less. The mother also devotes more time to them than most bees or wasps do.

Post showing both Carpenter Bee hole and and damage by woodpeckers drilling out bee larvae.

 Although this is usually just cosmetic and not structural damage, it can cause some harm and concern long term or if there are many holes. This is especially so since carpenter bees show great nest fidelity, with the young coming back and building in the same wood that their mothers used and often expanding existing tunnels even more. That means that preventing them from even starting is a huge factor in making sure they do not establish a colony. Although they may tunnel into stained wood, they do not like painted, pressure treated, or varnished surfaces. Filling the empty holes and/or screening them off also can greatly help.

Carpenter Bee cheating by robbing nectar from base of hole chewed at base of flower.

   Carpenter bees are actually beneficial insects and act, for the most part, as pollinators for many flowers. Their tongues however are not as long as some bumble bees and so sometimes cannot reach into deep flowers. That means that they sometimes "cheat" and chew a hole into the base of the flowers to steal nectar without providing pollination services, something that some other bees like honeybees also can do.

Carpenter Bee sleeping under the cover of a leaf and flowers.

     Though over the summer many carpenter bees, especially males, just hid under flowers and leaves to spend the night, many are now heading back to the holes to overwinter. They will remain dormant in these holes until spring arrives and they start the cycle all over again.
     There are many dangers to carpenter bees besides angry homeowners. One such danger is a creature who's whole existence depends on its carpenter bee hosts. A large fly called the Tiger Bee Fly (Xenox tigrinus) is often noticed hovering near carpenter bee tunnels. It is a parasatoid, laying its egg in the opening and then having its own larvae kill and eat the carpenter bee larva when it is pupating. Without carpenter bees there would be no Tiger Bee Flies, so they do not end up killing them all and are not a threat to people or the bee population as a whole.

Tiger Bee Fly
     Carpenter bees are not liked very much or are not well appreciated, but are fascinating and important parts of the natural world. They are intricately tied into the lives of flowers and of course the Tiger Bee Fly. Just something to think about the next time an inquisitive male buzzes you or you see one near the eaves of your porch.


  1. Another educational post! Love your blog thanks for keeping the stories coming.

  2. I need to have them relocate from the railing at my front door. They are chewing in under bottom rail. More each year. I see traps and read of wd40. I will paint to stop new holes but what is best to fill existing holes and will that make them relocate. I have an entire woods in my front yard. They are welcome there.