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by Barb Ogg, Ph.D.,
Extension Educator
Carpenter ants are important in the balance
of nature because they burrow and nest in dead trees and enhance
decay of the wood. They achieve pest status when a colony invades
and damages the integrity of the wood within a house. This fact
sheet will explain how the biology and behavior of carpenter ants
relate to control strategies when a homeowner is faced with this
problem.
Click on photos to enlarge
 Description
and Habits: The black carpenter ant, Camponotus
pennsylvanicus, is the most common carpenter ant species in
Nebraska. Foraging workers are 1/4 inch to 5/8 inch and black in
color. Another species, the rust-colored carpenter ant,
Camponotus ferrugineus, is a bit smaller and has a
reddish-orange thorax with a black head and abdomen. The most
diagnostic characteristic of all carpenter ants is they have a
one-segmented pedicel (the segment between the thorax and the
abdomen). The profile of the thorax is evenly rounded and not bumpy.
Click on photos to enlarge
 Most
carpenter ant workers are polymorphic—which means they are different
sizes. Entomologist refer to larger workers as "major" workers and
the smaller workers as "minor" workers. Each colony has at least one
"queen," the reproductive member that produces all additional
members of the colony. There may be more than one queen in a colony.
SWARMING ANTS WITH WINGS
When a colony gets very large (six- to ten-years-old and has more
than 2000 workers), it may produce winged reproductives, called swarmers. They are often produced during the summertime and may
overwinter in the colony. In our local area, we have people reporting
swarms of black carpenter ants in May and June. The males
often emerge first and are smaller than the females.
After mating, a single queen seeks out a suitable nesting site and
lays only a few eggs that hatch into maggot-like larvae. She cares
for the larvae that become the colony's first workers, forage for
food, and feed the young while the queen continues laying eggs.
The diet of carpenter ants is quite varied
and includes living and dead insects, honeydew from aphids, sweets,
meat, and fats. They do not eat wood. Workers leave the colony in
late afternoon or early evening, forage during the night, and return
to the colony in the early morning hours.
Carpenter ants carry food back to the nest
intact or ingested and later feed it to non-foraging members in the
nest. These ants may forage up to 100 yards from the nest to search
for food. Carpenter ants may become pests in houses by foraging for
food. The greatest concern, however, is they may cause serious
damage to wood in the structure. Unlike termites, they do not feed
upon wood, but merely use it as a place to nest.
Click on photos to enlarge
 Carpenter
ants construct their nests in hollow trees, logs, posts, landscaping
timbers, and wood used in homes and other structures. These ants
prefer to infest wood that is moist and rotting, but wood that has
been wet previously, may be soft enough to allow carpenter ants to
hollow it out and produce a colony. Certain parts of a house such
as: Around and under windows, roof eaves, decks, and porches are
more likely to be infested by carpenter ants. Refer to the diagram
on the back for the most common problem areas of a home.
Carpenter ants will use an old abandoned
nest or wood that has been "hollowed out" by termites. Nests may be
located in hollow doors or small void areas produced during
construction.
 Carpenter
ants may move from decaying portions of the wood into sound lumber
in the process of enlarging the nest. They cut galleries with the
grain following the softer parts of the wood. The ants leave harder
parts of the wood as walls separating the tunnels and cut openings
in these walls to allow access between tunnels. Access to the
outside may be through natural openings, or the ants may cut
openings where none exist naturally.
Click on photos to enlarge
 Carpenter
ants keep occupied galleries clean. They remove wood in the form of
a coarse sawdust-like material, which they push from the nest. This
often results in a cone-shaped pile accumulating just below the nest
entrance hole. This pile may include, in addition to the wood
fragments, other debris from the nest, including bits of soil, dead
ants, parts of insects and remnants of other food they ate.
Certain parts of a house are more likely to
be infested by carpenter ants. Refer to the following diagram for
most common problem areas of a home.
Control
see carpenter ant
bait
Colonies of many ant species can be
controlled with baits, but carpenter ants have such a varied diet,
baits are not always successful. Spraying insecticide on foraging
workers is of limited value because the queen will continue to
produce more young.
The secret to controlling carpenter ants is
direct treatment of the colony. Look for the piles of sawdust to
locate the entrance. Because worker ants move from the nest to
forage for food, their movements may lead to your discovery of the
nest opening. Inspect the entire structure and surrounding grounds,
because the nest or nests may be outdoors as well as in the
structure.
Once you find the colony, you can completely
eliminate the infestation by removing all the infested wood. But, if
there is a contributing moisture problem, be sure to fix it first.
If you cannot remove the infested wood, you can inject a
dust
formulation of an appropriate insecticide into the wall void. A
dust formulation is best, because the ants walk through the dust and
contaminate the colony. Introduce the dust into the nest through the
entrance hole using a hand duster with a tube with a tip that fits
snugly in the entrance. It may be necessary to enlarge the hole to
fit the duster. You can make a duster from a flexible plastic bottle
equipped with a tube tip. Fill the bottle no more than one-third
full, insert the tip in the entrance hole, and inject the dust by
alternately squeezing and releasing the pressure on the bottle. A
dust containing
boric acid is recommended for this
treatment. Also injecting damaged beams and wood with
Jecta can be very effective
at not only killing the ants but controlling fungus in the wood.
Click on photos to enlarge
 To
prevent further carpenter ant infestations, trim all trees and
bushes so branches do not touch the house and correct moisture
problems such as leaky roofs and plumbing. Paint and/or seal exposed
wood construction before it becomes wet. Replace previously ant- or
termite-infested wood, rotted, or water-damaged wooden parts of the
structure and eliminate wood/soil contacts. Remove dead stumps on
the property and store firewood off the ground and away from the
structure.
Carpenter ants will not kill living trees,
but openings in living trees are attractive to carpenter ants; these
openings should be closed. Stacks of firewood and old dead tree
stumps also attract carpenter ants. The longer wood remains
undisturbed, the more likely it will become infested. It is better
to keep on hand only the supply of firewood you plan to use during
one heating season. Store the wood off the ground and away from the
house. Spraying of firewood to protect it is of little value and is
not recommended. This resource guide was updated April 20, 2001
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