What to do if you see a carpenter ant in your house?

April 16—This story was originally published in May 2019.

Carpenter ants are among nature’s most efficient insects when it comes to breaking down and turning decaying or rotted wood into a natural compost.

But what’s good for the environment isn’t always a welcome presence in the home.

“A lot of people don’t like critters of any kind and consider them a nuisance if they see them in their home,” says Dr. Jody Green, lecturer in urban entomology at Nebraska Extension, University of Nebraska – Lincoln. “These types of ants fall under the category of ‘wood-destroying organisms’ and while it can take some time for damage to occur, people don’t like it when insects damage their homes.”

There are many species of carpenter ants in North America, but they are all recognizable by what Green describes as an evenly rounded thorax — the central body part of an ant to which the legs and wings are attached.

They are also usually larger than other ant species growing up to an inch in length. Depending on the species, they can be anywhere from reddish brown to solid black.

Carpenter ants prefer to nest in dead wood — and that could be decayed trees, logs, firewood or rotted beams and sills in a house, Green said.

What are the signs of carpenter ants in a house?

Strange as it may sound, you may hear carpenter ants in your home before you actually see them.

“They don’t eat the wood,” Green said. “But they’re excavating galleries and tunnels by chewing the wood with their jaws and you can hear it.”

That faint rustling sound of thousands of carpenter ants hard at work is a bit like what you hear when you pour the milk into a bowl of Rice Krispie granola.

The ants reduce the wood to coarse sawdust which, along with their excrement, the bodies of dead ants and the remains of their prey, are removed from the nest and tunnels by the worker ants.

This powdery substance is called “frass,” and piles of it on a table under an old beam, on the floor or next to a window could be the first visual sign of carpenter ants in the house, Green said.

It’s possible to live with carpenter ants that nest in a house for years and don’t even know they’re there, Green said.

“Often people notice them for the first time when they see the ‘flyers’ in the house,” she said.

Carpenter ants develop wings and only fly during mating in what entomologists call “nuptial flights.”

Mating occurs when the colony sends out ‘breeders’, the adult winged male and winged female carpenter ants to create a mating swarm.

“You may see them flying or crawling in your house,” Green said. “This is an indication that they are breeding and that you have a mature colony somewhere in your home.”

How do you get rid of carpenter ants?

The most common reaction from a homeowner who sees one or two carpenter ants crawling through the house is to grab a can of insecticide and spray them.

“That’s really not an effective solution,” Green said. “You only killed one or two ants out of a colony of thousands” [and] they’ll just send more collectors.”

The most effective way to deal with the problem is to find and destroy their nest or colony.

“That can be hard to do,” Green said. “The nest can be hard to find because they’ve been foraging until now – the ants can come from inside, from a neighbor’s house, from the woodpile in the back of the house, or from a rotten log [and] it can be hard to figure out.”

If the colony or nest is found in the house, it’s best to hire professional exterminators to deal with it, Green said. They have the proper equipment and are well trained in safe methods of destruction.

Ants that enter a home to forage for food can be tracked to their nest, Green said. They often use power lines or clotheslines to get from their colony to a home.

“They have a very well-rounded diet,” Green said. “They do eat sugar, but they also eat a lot of protein, which is why typical sugar ant baits don’t work for carpenter ants.”

There are DIY carpenter baits available at hardware or farm stores that contain proteins and other compounds they find palatable and can eat them, Green said. These products can help turn the tide on the shorter ants foraging in your home, she said, but won’t destroy the entire nest or colony. For that, she emphasized, you really need to hire professional exterminators.

As for any natural, non-chemical method of killing a colony, Green said she’s never heard of a method backed by solid science.

How do I prevent carpenter ants from entering my house?

To keep carpenter ants out, Green said the best defense is a good attack.

“It’s really up to us as people to shut down all the places they come in,” she said. “It’s also up to us to make sure our homes don’t have problems that attract ants [like] rotten or damp wood.”

Green said you can also remove old, rotten stumps from around the house and make sure your firewood stash is kept away from exterior walls and stacked on some sort of raised platform above the ground.

It’s also important to keep counter tops free of food crumbs or debris and to make sure food is sealed in airtight containers and stored securely so it doesn’t attract the foraging ants.

“They can do damage,” Green said. “How much depends on how big the colony is, but it’s not the worst and you have time to fix the problem; it’s not like your house is collapsing.”

Are carpenter ants good for anything?

Carpenter ants play an important role in an ecosystem, said Green

“If they weren’t there they wouldn’t be breaking down old wood to make wood waste and compost and that would be a shame,” she said. “They also eat many other insects that we consider garden pests.”

Carpenter ants are very effective predators, Green said, with a very structured social organization.

“The females do all the work and they all have work to do,” she said. “Some care for the brood and others forage for food and others care for and feed the queen ant that lays all the eggs.”

All these “sister ants” take care of each other and communicate with the help of pheromones.

Although there are always a few males in the colony, the larvae only develop into males in large numbers leading up to the mating season.

Are carpenter ants dangerous to humans?

With their large, wood-cutting jaws, carpenter ants can deliver a pretty good bite when threatened, and it can hurt, Green said. They also produce a form of acid that they can spray as a defense.

“I’ve never been sprayed,” said Green. “But in conversations with people who have it, I’ve been told that it can be quite painful to the lungs if you breathe it in.”

For the most part, Green said, the carpenter ant just wants to be left alone to take its place in the ecosystem, regardless of whether your home is in its path.

“We are the ones who make them a plague,” she said. “It’s not the ants’ fault that we build our homes on top of their colonies.”

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