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Big Black Ants In Homes

- Carpenter ants can cause extensive damage in homes -

Summary: The large (1/4"-1/2", or even larger) black ants that are found in homes and outside are carpenter ants (Camponotus spp.). These powerful ants nest in cavities, not in the soil like other ants, and can cause damage when nests are built in our homes.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Big ants in homes

You may occasionally find large (1/4"-1/2") black, or red and black, ants around your home, in the landscape or even indoors. While most ants are much smaller (1/8" or less) and generally lighter in color, these big black ants are carpenter ants (Camponotus spp.) and are noteworthy because they can cause structural damage to homes.

The key to identifying a carpenter ant is usually size (at least in the US). Carpenter ants are generally, but not always, the largest ants most people will encounter. Carpenter ants also differ from other ants in that they nest above ground in cavities that are expanded as their colonies grow.

big black ant - carpenter ant

Big black ant found around homes are carpenter ants.


Carpenter ant damage

If carpenter ants establish a nest in your home they can cause damage, sometimes extensive and costly damage, to structural wood, subflooring, sheathing, and rigid foam insulation. Damage occurs when these large powerful ants expand their nests into sound building materials. Nests can also split so that a single large nest becomes two or more satellite nests in different parts of the house.

Carpenter ants that nest outside cause no damage and pose no particular threat as long as they remain outside. Carpenter ants are very common in many areas and so you should not be alarmed if you find some outdoors.


The most important thing you can do to protect your home from carpenter ant damage and other structural pests is to do regular pest and dry-rot inspections (see Related Articles below) and to promptly treat problems when they are found. There is no need for "periodic maintenance treatments" that are sometimes advocated by pest control companies. See Carpenter Ants And Their Control for details including the use of specialized baits.

Related Articles

DIY House Inspections for Structural Pests
 

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Jack DeAngelis, PhD,  , email:  [email protected]

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