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carpenter ants

To: This Old House 9-24-2012

I have a question about carpenter ants.

We live in north-central Illinois. In December 2007 we bought a ranch house that was constructed around 1955. I think it would be called wood-frame with brick exterior.

The master bathroom has a stall shower. We didn’t know it at the time but the stall was leaking a little bit. After a spell (maybe a year) we realized this, and after another spell (maybe another year) I found the leak and sealed it.

Several weeks after this repair we started noticing carpenter ants. For the most part these were individual ants on the move in the hallway leading to/from this bathroom. We had never seen any ants previously. We hired an exterminator and he found a nest in the basement ceiling under the shower pan. Apparently the moisture from the leak had attracted them. He placed bait and it seems all the ants were killed.

In addition to (following) the bait, the remedy has included (for about the past two years) semiannual application of some sort of spray chemical repellent at the foundation around the house perimeter. This all seems to be pretty successful; we’ve seen 2-3 ants in the house each of the last couple summers.

We’ve been advised that the perimeter treatments should be done in perpetuity because ants can sense the damaged wood under the shower and will be attracted to it. At first blush this made perfect sense to me.

But I’ve also thought: It seems the ants were perfectly happy (staying) in their nest under the shower so long as the shower was leaking and the wood there was moist. But it seems that once the leak was fixed and the wood started to dry they became less satisfied. I’m speculating here but since we did not see them until the leak was fixed, it seems perhaps they were (afterward) striking out looking for a better location.

IF that might be true it begs the question of whether they – which is to say, today, any ants exterior to the house – would be attracted to the damaged wood under the shower. And that would call into question the need to continue to spray the perimeter chemical barrier every year.

If you have an opinion about the necessity for the annual perimeter treatments we’d love to hear it.


Re: carpenter ants

As carpenter ants bore their nests, they leave behind several piles of fibrous, finely shredded sawdust-like material called “frass”. Frass is better produced when the wood is wet. Yeah, your going to need annual treatments, unless you want to stop showering!

Re: carpenter ants

Every ant bait treatment/application fades with time. That's why you need to repeat.

Also, the chemicals used today are not as potent as they used to be, due to new gov't EPA regulations.

Re: carpenter ants


AHHH yes, the good old days of Chlordane. I remember them like it was yesterday.

What DJ said is right, the new bug sprays are not nearly as effective as we remember or would like them to be.

Re: carpenter ants
HoustonRemodeler wrote:


AHHH yes, the good old days of Chlordane. I remember them like it was yesterday.

What DJ said is right, the new bug sprays are not nearly as effective as we remember or would like them to be.

I have to partly disagree with you on this one. Sodium Borates are very effective. The only issue with them is that they are water soluble and have to be reapplied periodically. If they are put on wood that does not get wet, then they last forever. Products like Chlordane and Dursban are oil based and have more sticking power.

Borates were the chemical of choice for most of the last millennium, until about two centuries ago. The more toxic chemicals began to be used. Interesting that there are houses and buildings made from wood that have stood for up to a 1000 years in Europe. Many buildings over 200 years old that were treated with borates are still in good shape, but buildings built in the last 200 years are not in as good a shape. Historic buildings less than 200 years old are kind of rare. Makes you wonder doesn't it.

But there are some less effective chemicals also in use out there.

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