Q: Can you tell me why black ants have appeared in the second floor of my house? We usually find only one or two, and they've been popping...

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Q: Can you tell me why black ants have appeared in the second floor of my house? We usually find only one or two, and they’ve been popping up in various rooms — so no real discernible pattern. Is this considered normal or an indication of something bigger? How do I best combat them?

A: What you describe sounds like carpenter ants. These black ants are part of nature’s cleanup crew, helping to rid the world of decaying wood, dead insects and other debris. But they need to be conducting business outdoors — in old logs and trees — not in your house. Carpenter ants are destructive to a home’s wood structure. (For a picture of a carpenter ant and the type of damage they do, go to www.extension.umn.edu/distribution/housingandclothing/DK1015.html.) The ants you see may or may not be a problem.

An occasional carpenter ant or two in your home may be scouts that made their way indoors to snoop around. But if ants are actively cruising the house, or you see more than just a few, they probably have made a nest inside.

Because carpenter ants like damp wood, areas that are or have been wet are an invitation to them to move in, make a satellite nest and start chewing. Consider:

• Clogged gutters can cause fall rains and winter snowmelt to back up and spill into soffit areas or down exterior walls.

• Extensive and persistent window condensation can leave framing damp and attractive to ants.

• A slow plumbing leak may be dampening areas behind walls and floors.

• Faulty flashing (material that sheds rainwater) around chimneys, skylights, windows or doors also creates damp spots.

Finding and destroying nests — indoors and out — is the way to end the infestation. You also must solve the moisture problem and replace any damaged wood to prevent reinfestation.

The Minnesota Extension Service suggests that homeowners use baits listed for use on carpenter ants. Those that use boric acid as an active ingredient may be slow-acting, but they can be effective.

Because finding and treating nests can be difficult, hiring a pest-control company to do the job may be your best choice. Such companies also have access to chemicals not available to consumers. Look for a company that will find and treat the main nest outdoors as well as any satellite nests indoors. Once a property is effectively treated, a regular spraying schedule for carpenter ants is unnecessary. You just need to keep the house dry and well-maintained.

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