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CARPENTER ANTS
by Mike Potter, Extension Entomologist
Courtesy
of University of Kentucky College of Agriculture
"I keep seeing big, black ants in my house, especially in the kitchen
and bathroom. I spray the ones I see, but they keep coming back. What kind of
ants are these, where do they come from, and how do I get rid of them?"
These are the questions typically asked by homeowners who have
carpenter ants. Carpenter ants are one of the most common
ants found in Kentucky. They are also one of the most difficult to control. This
publication will help you determine if you have carpenter ants, and provide tips
on how to control them.
Biology and Habits
Carpenter ants, vary in size and color but are usually large (1/4-1/2 inch)
and blackish. Occasionally, swarms of winged carpenter ant reproductives will
emerge inside a home. Carpenter ant swarms usually occur in the spring and are a
sure sign that a colony is nesting somewhere inside the structure.
Winged carpenter ants can be distinguished from
termites by their larger size and shape of their antennae, waist and wings.
Besides being objectionable by their presence, carpenter ants damage wood by
hollowing it out for nesting. They excavate galleries in wood which have a
smooth, sandpapered appearance. Wood which has been damaged by carpenter ants
contains no mud-like material, as is the case with termites. Shredded fragments
of wood, similar in appearance to coarse sawdust, are ejected from the galleries
through preexisting cracks or slits made by the ants. When such accumulations
are found (typically containing dead ants and bits of insects which the
carpenter ants have eaten), it's a good indication that a carpenter ant nest is
nearby. Oftentimes, however, the excavated sawdust remains hidden behind a wall
or in some other concealed area.
Carpenter ants nest in both moist and dry wood, but prefer wood which is
moist. Consequently, the nests are more likely to be found in wood dampened by
water leaks, such as around sinks, bathtubs, poorly sealed windows/ door frames,
roof leaks and poorly flashed chimneys. Nests are especially common in moist,
hollow spaces such as the wall void behind a dishwasher, or in a hollow porch
column. Since there often will be no external signs of damage, probing the wood
with a screwdriver helps reveal the excavated galleries. Another technique for
locating hidden nests is to tap along baseboards and other wood surfaces with
the blunt end of a screwdriver, listening for the hollow sound of damaged wood.
If a nest is nearby, carpenter ants often will respond by making a "
rustling" sound within the nest, similar to the crinkling of cellophane.
Carpenter ants may establish nests in a number of different locations. It is
important to realize that these locations can be either inside or outside the
structure. Carpenter ants actually construct two different kinds of nests:
parent colonies which, when mature, contain an egg-laying queen, brood
and 2000 or more worker ants, and satellite colonies which may have large
numbers of worker ants but no queen, eggs or young larvae. The carpenter ants
inside a home may have originated from the parent colony or from one or more
satellite nests. For example, the ants may be coming from the parent nest
located outdoors in a tree stump, landscape timber or woodpile, or from one or
more satellite nests hidden behind a wall in the kitchen or bathroom, or perhaps
from wood dampened by a roof leak in the attic.
The extent and potential damage to a home depends on how many nests are
actually present within the structure, and how long the infestation has been
active. Although large carpenter ant colonies are capable of causing structural
damage, the damage is not normally as serious as that from termites. In some
cases, the damage may be relatively insignificant, but this can only be
determined by locating and exposing the nest area.
Control
The best way to control carpenter ants is to find and destroy the nests. This
is often easier said than done. Recent studies have shown that carpenter ants
follow distinct scent trails between the satellite colonies and the parent nest.
Carpenter ants also rely on scent trails to recruit their nestmates to food.
With patience and a little effort, homeowners can use this trailing behavior
displayed by carpenter ants to locate and eliminate the nests.
When carpenter ants are observed, don't spray them; instead, feed the
ants small dabs of diluted honey placed onto the back (non sticky side) of pieces
of masking tape. The best time to do this is late at night since this is when
carpenter ants are most active. After the ants have fed on the honey, follow
them on their journey back to their nest. Be patient-- eventually the
ants will disappear behind a baseboard, cabinet, or into some other concealed
location such as the hollow space (void) within a wall, door casing, or porch
column.
Treat wall voids and other hidden spaces where ants are entering by
carefully drilling a series of small (1/8 inch) holes and
puffing boric acid (available at most hardware stores) into the suspected
nest areas. The boric acid powder will disperse in the hidden void and contact
and kill the ants. If you suspect the nest is in a wall, drill and treat at
least 3-6 feet on either side of where ants are entering so as to maximize the
chances of contacting the nest. Carpenter ants prefer to travel along wires,
pipes and edges. If you suspect the nest location is in a wall, also treat
behind pipe collars and behind --not in-- the junction box for electrical
switch plates/receptacles. NEVER SPRAY LIQUIDS OR INSERT METAL-TIPPED DEVICES
AROUND ELECTRICAL OUTLETS!).
As noted earlier, carpenter ants seen in the home may actually be nesting
outdoors, foraging indoors for food and/or moisture. Consequently, the
homeowner may end up following the ants they have baited with honey out of the
house and into the yard, possibly to a nest located in a stump, or under a log
or railroad tie. Once the outdoor nest is discovered, treatment can be performed
by spraying or drenching the nest with an insecticide such as carbaryl (Sevin),
diazinon, or chlorpyrifos (Dursban). If outdoor nests are suspected, the
homeowner should also inspect around the foundation of the building at night
with a flashlight, especially around doors, weep holes and openings such as
where utility pipes and wires enter the structure. The baiting approach using
honey can also be used to trace carpenter ants which are foraging outdoors back
to their nest.
Tips When Calling a Professional
Oftentimes, it will be difficult or
impossible to locate and destroy the carpenter ant nest(s). In this case, the
homeowner may wish to call a professional pest control operator. Pest control
companies approach carpenter ant problems differently. Some attempt to locate
the nest and selectively treat only in specific areas. Other companies take more
of a "shot-gun" approach, drilling and dusting as many potential wall
voids and nesting sites as possible. Most companies also apply a perimeter spray
treatment around the outside foundation of the home in an effort to temporarily
prevent reinvasion. The approach which should not be used is simply to
spray each month where carpenter ants are seen. If no effort is made to locate
the nest(s) or probable nest areas, the problem will most likely continue.
Typically, there will be wide differences in price depending on the company
and amount of effort expended. Since carpenter ant problems are not always
solved on the first attempt, the type of guarantee and reputation of the company
should be factored into the purchasing decision.
Carpenter Ant Prevention
- A number of steps can be taken by homeowners to reduce the potential for
future carpenter ant problems.
-
-
Correct roof leaks, plumbing leaks and other moisture problems which will
attract carpenter ants.
-
Eliminate wood-to-ground contact such as where landscaping has moved soil or
mulch up against the wood siding of a home.
-
Clip back tree limbs and vegetation touching the roof or siding of the
house. Limbs and branches serve as "bridges" between carpenter ants
nesting in a dead tree limb and the structure.
-
Seal cracks and openings in the foundation, especially where utility pipes
and wires enter from the outside.
-
Stack firewood away from the foundation and elevate it off the ground. Never
store firewood in the garage or other areas of the home, as firewood is a prime
nesting area for carpenter ants.
CAUTION! Pesticide recommendations in this publication are
registered for use in Kentucky, USA ONLY! The use of some products may
not be legal in your state or country. Please check with your local county agent
or regulatory official before using any pesticide mentioned in this publication.
Issued: 2/93
Revised: 11/97
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