The black carpenter ant, Camponotus pennsylvanicus (DeGreer),
is a native species and the common species in the east. Camponotus
modoc Wheeler is the common western species. These ants get
their common name from their habit of hollowing out galleries
in pieces of wood for nesting purposes. This nesting habit
can result in structural damage. Carpenter ants are found
throughout the United States.
Workers polymorphic, large (1/8-1/2" or 3.5-13 mm) but
vary greatly in size; queens about 112-518" (13-17 mm)
long. Color black, combinations of red and black, or completely
red or brown. Antenna 12-segmented, without a club. Thorax
lacks spines, profile evenly roundedd on upper side. Peel
1-segmented. Gassier with anal opening round, surrounded by
circlet of hairs. Stinger absent. Workers capable of emitting
a strong formic acid odor.
pennsylvanicus with workers about 1/4-1/2" (6-13 mm)
long and completely black except top of gaster with long,
pale yellowish hairs pressed against its surface. Camponotus
modoc with workers about 1/4-1/2" (5-11 mm) long, dull
black with reddish legs and with golden hairs covering abdomen.
Queens up to 5/8+" (17+ mm) long. Other species black,
various combinations of red and black, or completely red or
brown. Although carpenter ants do not sting, their bites can
be quite painful, especially when they inject formic acid
into the wound.
(1) Dark field (Formica spp.), larger yellow (Acanthomyops
interjectus), and Allegheny mound (F. exsectoides) ants have
profile of thorax not evenly rounded, with distinct impression(s);
in addition dark field ants with front and hind margins of
node steeply or equally sloped. (2) Velvety tree ants (Liometopum
spp.) lack circular anal opening surrounded by circlet of
hairs. (3) Other medium to large dark ants with 2-segmented
The only external indication of infestation other than the
presence of workers and/or swarmers is the appearance of small
openings or windows on the surface of the wood. Through these,
the workers expel debris which consists of sawdust-like shavings
and/or fragments of insulation and insect body parts. The
accumulation of such debris below such holes is a good indication
of an infestation.
the galleries follow the softer spring wood with numerous
connections through the harder/dark summer wood. The gallery
walls are smooth, with a sand-papered appearance. The active
galleries are kept clean of debris.
prefer to attack wood softened by fungus and are often associated
with moisture problems.
Black carpenter ant colonies are of moderate size, usually
containing over 3,000 workers (up to 10-15,000 including satellite
nests) when maturity is reached in about 3 to 6 years. The
typical western carpenter ant (C. modoc) mature colony contains
about 10-20,000 workers, with large colonies having up to
100,000 workers. Developmental time (egg to adult) for workers
takes at least 60 days. Workers are polymorphic, with majors,
minors and intermediates present. There is usually only one
functional, wingless queen per colony. Swarmers are not produced
until the colony is more than 2 years old, usually 3.5-4 years
old for C. pennsylvanicus and often 6-10 years old for C.
modoc. Swarmers appear from May until August in the east and
from February through June in the west.
Most carpenter ant species establish their first nest in decayed
wood and later expand or enlarge this into sound wood. Inside,
nests are located in wood (preferably softened by fungus rot),
in insulation, and/or in wall voids. Workers are a nuisance
when out searching for food but are destructive to timbers
utilized for nesting activities. Outside, nests are typically
located in rotting fence posts, stumps, old firewood, dead
portions of standing trees, and under stones or fallen logs.
presence of a carpenter ant nest is sometimes indicated by
a rustling sound coming from wall voids or from wood where
the colony is located. Otherwise, the emergence of swarmers
indoors may be the first indication of an indoor colony.
ants feed primarily on insect honeydew, plant and fruit juices,
insects, and other arthropods. Inside, they will also feed
on sweets, eggs, meats, cakes, and grease.
workers forage for distances of up to 300 feet (91.4m) from
the nest. They typically enter buildings around door and window
frames, eaves, plumbing and utility lines, and shrub and tree
branches in contact with the building. Although some workers
are active during the day, most activity is from dusk till
dawn, with peak activity between 10 pm and 2 am. The trail
between the parent and satellite nest is usually about 1/4-13/16"
(6-20 mm) wide and is kept clear of vegetation and debris.
It usually follows contours but typically will cut across
The first step is to determine if the ants present are merely
foraging inside or if there is a nest inside. The best indication
of a nest is the presence of sawdust piles containing insect
body parts. Another indication is the sound produced as the
workers remove wood to expand the nest. Outside, check around
the building's perimeter for foraging trails, especially in
the direction of trees and shrubs; easiest to locate between
sunset and sunrise when the ants are most active.
second step is to locate any inside nests. Look for sawdust
piles with insect body parts. Listen for ant sounds mentioned
above; listening devices are helpful. Gently tap with a screwdriver,
etc. all exposed wood such as floor joists, sill plates, roof
rafters, etc. and listen for sound changes; nest cavities
give a hollow or dull ring. Check suspicious areas with a
knife blade which will readily penetrate infested wood. Be
sure to check crawl spaces, basements, and attics. Carpenter
ants have a network of trails they follow throughout a structure
and often use the tops of electrical Wires and water pipes,
so be sure to check where these are. A moisture meter can
be helpful in locating areas of higher moisture in which the
ants prefer to locate their initial nests.
third step is to determine if the inside colony is a parent
or satellite colony. Inspect and search. Detection of a trail
directs one to the parent colony. For effective control, it
is imperative to locate and eliminate the parent colony.
the colony or colonies are located, they should be treated
directly with an appropriately labeled pesticide. Inside,
this may involve drilling wall voids and applying dust and/or
drilling wood members and pressure injection. Barrier treatment
is effective in preventing entry, with wettable powder and
microencapsulated formulations working best. All branches
of trees and shrubs in contact with the building must be trimmed
back. Be sure to check where electrical and water lines enter
the building and caulk any gaps. Sometimes treating the bottom
3-6 feet (1-2 m) of tree trunks and/or utility poles is helpful.