We have taken numerous calls about carpenter ant nests in
trees. Carpenter ants normally do not need to be controlled
in trees because they usually cause little or no damage to
the tree.
Carpenter ants vary in size and color. The black
carpenter ant is probably the most common species in
landscapes. Worker ants are nonreproducing females that are
wingless and black. Workers come in two size ranges. Minor
workers are approximately 1/4 inch long and do much of the
food foraging, nest construction, and larval feeding; they
also attend the queen. Major workers are also wingless and
black, but are about 1/2 inch long and play a major role in
defending the nest and minor workers.
The black carpenter ant is the only carpenter ant in
Illinois that commonly locates its nests in buildings. They
tunnel out wood that is damp or decaying from roof or water-
pipe leaks. (The red carpenter ant is another common
species, with red, wingless workers that are about 1/4 inch
long. Other, smaller species of carpenter ants are also
found in Illinois.)
Carpenter ants build their nests by hollowing out rotting
wood; they do not eat the wood. Workers take mouthful-sized
chips of wood to the nest entrance, where they deposit the
chips. This results in a pile of coarse sawdust at the base
of a tree. The nest itself consists of meandering, 1/4-inch-
diameter tunnels that are free of sawdust. Egg laying,
larval rearing, and pupation take place within these
tunnels. Nests may be present in rotting wood in trunks,
limbs, or roots.
Nests that are at least five years old will contain
winged reproductives. Black carpenter ant males are 1/4 inch
long and have two pairs of clear wings. The queens are
approximately 3/4 inch long and also have two pairs of clear
wings. Both sexes emerge from the colony in early morning
and fly towards the light to escape the colony. Mating
occurs, and the reproductives break their wings off at
weakened spots. Then they tunnel into damp, rotting wood to
start a new colony.
Carpenter ant nests in trees are an indication of rotting
wood. Such trees should be checked to determine whether the
rot has weakened the tree enough that it becomes a hazard.
Nests in trees close to a house may result in ants entering
the house to forage. This nuisance can be eliminated by
spraying diazinon into the nest or by pruning overhanging
limbs at least three feet back from the roof. Otherwise,
carpenter ant nests do not directly weaken the tree and do
not usually require control.
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