Carpenter Ants in Iowa Homes: Signs, Nests and Fixes

Updated 2026-10-26 · By Kasey, Waukee, Iowa

If you keep finding big, shiny black ants in the kitchen of your Johnston home, or a little pile of sawdust near a windowsill in Urbandale or Grimes, carpenter ants are a likely suspect. Iowa State University (ISU) Extension says carpenter ants are very abundant in Iowa and are common pests in homes and other buildings.

The good news is that carpenter ants usually point you to a fixable problem. They like wood that is soft or damp, so finding them is often a nudge to look for a leak or rot. This guide covers how to recognize them, how to track down the nest, what you can do yourself, and when it makes sense to call a licensed Iowa pest professional.

What it is and how to identify it

ISU describes the most common carpenter ants as the familiar "large, black ants" that are one-half inch or more in length and shiny black. ISU's common ants guide lists the black carpenter ant at 1/2 to 3/4 inch with one node (the small bump at the waist). Not every carpenter ant is big and black, though. ISU notes some kinds are as small as one-quarter inch and reddish-brown or two-toned.

The one trait all carpenter ants share, according to ISU, is a smoothly rounded outline of the thorax (the middle section) when you look at the ant from the side.

Winged ants in the house

ISU says winged ants, called swarmers, may show up in the home at times. They are males and females leaving a healthy, well-established colony to try to start a new one, and most of them die. Carpenter ant swarmers are recognized by their large size, one-half inch or more. Because all ant species can produce swarmers, size helps tell them apart from other ants.

Not sure what you have? Our guide to common Iowa ants walks through the other species. The ISU Plant and Insect Diagnostic Clinic also identifies insects for Iowans. Check its website for current forms, fees and mailing instructions before sending a sample.

Signs of carpenter ants (and how they differ from termites)

ISU is clear that carpenter ants do not eat wood. They chew tunnels and cavities to make a nest and push the wood out as coarse sawdust. That sawdust pile may also contain dead ants and insect parts. ISU calls the presence of sawdust an important clue in finding a nest.

ISU lists common nest spots, including:

• Stumps, logs, hollow trees and dead limbs
• Landscaping timbers, deck and fence posts
• Porch columns, windowsills, and door and skylight frames
• Building framing and roofs
• Existing gaps such as hollow doors and spaces around windows and doors

According to ISU, carpenter ant galleries look different from termite damage. They are free of soil and powdery wood, the walls are so smooth they look sandpapered, and the tunnels do not follow the grain of the wood, unlike termite galleries.

Why it shows up (season and local angle)

ISU says carpenter ants prefer naturally soft wood or wood softened by moisture and decay. That is the local angle for many Johnston and Grimes homes with decks, landscaping timbers and big shade trees: anywhere wood stays wet is attractive. ISU also warns that the decay from excess moisture is often more damaging to the building than the ants. Moisture is not strictly required, though; ISU says nests can extend into dry, sound lumber and foam insulation boards.

Timing gives you a clue about where the ants are coming from:

• In winter, ISU says carpenter ants found indoors usually come from a nest somewhere inside the house.
• In spring and summer, or on very warm winter days, they could be wandering in from outdoors, or they could be foragers from a nest in a wall or ceiling.

Trees matter too. ISU's article on carpenter ants in trees says a colony inside a tree can form satellite colonies inside a nearby home wall.

What you can do yourself

ISU says carpenter ant control can be a do-it-yourself project or a job for a professional. Either way, the order matters.

1. Find the nest first

ISU says locating the source is as important as it is difficult, especially if you only see a few ants at a time. Its suggestions:

• Watch for a pattern of movement. In spring and summer, carpenter ants are more active at night, so check with a flashlight after sunset, inside and outside the house.
• Look for sawdust under windowsills, door frames, porch columns and deck posts.
• Check carefully before treating anything, since winter ants and summer ants can mean different sources.

2. Treat the nest, not the whole house

ISU says the best control comes from locating and treating the nest, indoors or out, with a small amount of insecticide applied directly into it. Reaching a hidden nest may mean lifting molding or drilling small holes, which is often where a pro helps. If you find a nest while remodeling, ISU says you can also vacuum up the ants and discard them.

If you cannot find the nest, ISU's fallback indoors is to treat room edges, cracks and crevices where workers are active, to wear the colony down over time.

3. Fix the wood and the water

ISU recommends you replace damaged or decayed wood and seal the structure to stop future moisture problems. Check gutters, roof leaks, rotting window trim and any wood that touches soil. Without this step, the ants have a reason to come back.

A few product cautions from ISU

• Household products for this are usually sold as ready-to-use ant and roach sprays or home insecticide sprays, plus dusts such as boric acid or diatomaceous earth. We do not recommend specific brands.
• Do not use lawn and garden insecticides indoors.
• Over-the-counter sweet ant baits may not eliminate carpenter ants. ISU says specially formulated carpenter ant baits used by professional pest managers have been very effective.
• Monthly spray treatments are not recommended for carpenter ants.

When to call a licensed pro

A professional can make sense when:

• You cannot find the nest after a few evenings of watching.
• The nest is inside a wall, ceiling or roof and reaching it means drilling or removing trim.
• You see ants indoors in winter, which ISU says usually means a nest inside the house.
• You find sawdust plus soft or rotting wood, since the moisture damage may need a contractor as well as pest work.
• You want access to the professional carpenter ant baits ISU mentions.
• You are not sure whether it is ants or termites.

ISU's advice on hiring is simple: shop around and compare prices and services.

How to choose a licensed Iowa applicator

Under Iowa's administrative rules, anyone in the business of applying pesticides to another person's property must be licensed and certified by the state. Household pest work is Category 7A, General and Household Pest Control. Before you hire:

1. Ask for the company's Iowa license and the technician's certification.
2. Verify both in the Iowa Department of Agriculture and Land Stewardship lookup.
3. Ask how they plan to find and treat the nest, and whether they will point out moisture or rot that needs fixing.

See our guide to choosing a pest pro for more questions to ask.

Frequently asked questions

Do carpenter ants eat wood?

No. ISU says carpenter ants do not eat wood. They chew tunnels to nest in it and push out coarse sawdust, which is often the best clue to where the nest is.

Why am I seeing carpenter ants inside in winter?

ISU says carpenter ants found indoors in winter usually come from a nest somewhere inside the house. That is a good reason to look for the nest or call a licensed pro.

How can I tell carpenter ant damage from termite damage?

ISU says carpenter ant galleries are free of soil and powdery wood, have smooth, sanded-looking walls, and do not follow the grain of the wood. Termite galleries do follow the grain.

Will regular ant bait get rid of carpenter ants?

Often not. ISU says over-the-counter sweet ant baits may not eliminate carpenter ants, while specially formulated carpenter ant baits used by professionals have been very effective.

Should I cut down a tree that has carpenter ants?

Usually not. ISU says carpenter ants in trees are taking advantage of wood that is already decayed, and cutting down an otherwise healthy tree is generally not necessary. A colony in a tree can spread to a nearby home wall, so keep an eye on the house.