A Northeast Region Program

Dennis Reidenbach
Regional Director

CARPENTER BEE Xylocopa spp

 INTRODUCTION

In the Northeastern, where carpenter bees are starting to be a problem on Historic Wooden Structures, systematic monitoring for carpenter bees on vulnerable resources should begin in late March or early April. Habitat modification (wood painting, hole filling) should be attempted as a first course of action.

The carpenter bee is a valuable plant pollinator and should be killed only as a last resort.

BIOLOGY

Identification: Carpenter bees are large and robust insects resembling bumble bees. They are usually about one inch long and colored metallic blue black with green or purplish reflections. They differ from bumble bees by having a shiny, hairless abdomen. Male carpenter bees have a yellow face and females have a black face. Male bees have no stinger, and although females carpenter bees are capable of stinging, they very seldom do.

Life cycle: Carpenter bees overwinter as larvae in the wood. Those that survive the winter mate from April to June, then begin preparations for the next generation. Adult female carpenter bees bore holes into wood overhangs, fence posts, and trees. When they bore into wood, it is usually a hole about ½ inch in diameter. The hole will usually go straight in for about two inches and then turn 90 degrees. Eggs are laid at the end of this chamber. Food (bee bread) is placed along side each of the eggs and then the chamber is sealed off with chewed up wood. The female carpenter bee will defend the hole/chamber aggressively. Egg chambers are reused each year by the resident female bee. If the chamber is occupied by another bee, the resident female will start another hole close by. If the bees are allowed to return year after year unchecked, a piece of wood/structure can have as many as 100 active holes at one time. The issue of carpenter bee management needs to be addressed at the first sign of wood damaging activities.

Social Behavior: The male carpenter bee will buzz loudly around humans who approach "his" egg hole/chamber. The buzzing is merely a sign of curiosity and represent no actual threat to humans. The female bee will also fly at humans as they approach her egg chamber. Although the female does have a stinger, very few people are actually stung by female carpenter bees each year.

Environmental conditions that favor development: Carpenter bees are Spring and early summer visitors. In choosing a nesting site, the female will first return to the site where she was born. In the selection of a nesting site, carpenter bees prefer unpainted or nonvarished softwoods. When forced to find a new nesting site, female carpenter bees will look for wood surfaces that are pitted, dented, or has depressions. Carpenter bees will not attack wood that still has bark on it.

Natural enemies: Woodpeckers are common predators of the immature bees.

MANAGEMENT

Medical importance: The carpenter bee represent a minor medical threat to humans and their pets. The male, although extremely aggressive in his behavior, is not capable of stinging or biting a human. The female is capable of both biting and stinging a human, but records show that she seldom does. The carpenter bee is not known to carry any diseases that would threaten the health of humans.

Potential damage: Carpenter bees chew with their mouthparts into wooden structures such as fences, telephone poles, bridges, wooden water tanks, and various parts of wooden buildings. The holes they chew are about ½ inch in diameter and can be up to 2 feet long. Once a carpenter bee has laid eggs at a site, unless the site is altered and made unfavorable, the bee will return year after year to lay eggs (damage the wood).

Threshold: The threshold (the number of carpenter bees necessary to generate concern and action) for carpenter bees depends on the wood that is being damaged. If the bees are chewing on a piece of wood with little value, the threshold would be higher that if the damage was being done to a Historic Home. We carpenter bees are chewing on wood that has value, the threshold is one bee (the very first bee that arrives). Upon arrive of the very first female bee, efforts should be made to alter the effected wood to make it less attractive to all current and further carpenter bees.

Monitoring: The critical time for monitoring the carpenter bee is from March until July. During this time period, the park should carry out a systematic survey of vulnerable resources. Depending on the value of the vulnerable resources, the size of the park unit, and the manpower available, the survey should be frequent enough to avoid missing the initial emergence of the overwintering bees. Although the bees chew fairly slowly, a significant amount damage can be done in a week. Critical sites that should be included in monitoring surveys of buildings are the trim, exposed rafters, roof and porch beams, window sills, soffits, and under shutters. Keep records of when and where carpenter bees are observed the park so necessary repairs and modifications can be made. Long term monitoring information will always allow to better time your management efforts next year and the years beyond.

MANAGEMENT STRATEGIES