A Northeast Region Program
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
The carpenter bee is
a valuable plant pollinator and should be killed only as a last
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
¾ inch long
hairless abdomen; males have no stinger; to not have special
structures on rear legs to carry pollen;
¾ inch long
all over their bodies; possess a stinger; possess special structures
on rear legs for carrying pollen
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.
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.
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.
Woodpeckers are common predators of the immature bees.
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.
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
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.
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.
instructional information and guidance on the carpenter bee
to all park employees. The more the park staff knows about the
appearance, the biology, and the damage that the bees can cause,
the easier it will be to properly address the management of
the winter, before the critical Spring emergence of the overwintering
Coordinator, Interpretive Staff, Maintenance Staff
cracks, holes, and dent on all susceptible wood surfaces.
bees tend to choose cracks, holes, and dents on susceptible
wood for their nesting sites. Holes should be filled with materials
that are hard enough to discourage carpenter bee chewing. On
sites where caulking and putty are not working, metal and fiberglass
screening can be fastened over the filled holes to farther discourage
during, and after Carpenter bee damage occurs.
all untreated wood.
covered with varnish or paint is not as attractive to the Carpenter
bee for nesting sites.
July and March of the year.
damaged softwoods with less susceptible hardwoods.
bees are much more likely to utilize softwoods (pine, fir, redwood,
cedar) as nesting sites.
repairs are made.
effected and replace wood with borate materials.
(Timbor- for green wood, Boracare-seasoned woods) have been
shown to be effective in discouraging wood infesting insects.
The borate material can be applied to wood as it is used in
new construction or on wood that is being used in repairs. Borate
treated wood remains coated longer if it is not in direct line
with rain and water.
application are best made during the summer after all repairs
have been made from the previous Spring.
Silica gel based material into the nesting tunnels and then
gel applied to the nesting tunnel (hole), after the female has
left the nest, will kill the larva as it attempts to emerge
the following Spring. After applying the silica gel, the nesting
hole should be closed up from the elements protect the gel from
the environment. Because the adults are valuable pollinators,
efforts should be made not to kill them.