Last year I had an infestation of carpenter ants, so I contacted a pest control company and paid for a year's worth of service. Now, exactly a week after the contract expired, I'm seeing them come back.

I'm planning on taking care of it myself this year, since the chemicals cost less than a month's worth of service from the pest control company.

I know that the two most common ways of treating for carpenter ants are:

1.) Boric acid bait

2.) Fipronil spray

Is either one of these treatments more effective than the other, and/or is the combination of these treatments more effective than either on its own?

  • How did the contractor do it? repeat as it obviously worked...
    – Solar Mike
    Apr 16, 2019 at 13:18
  • The contractor used both. That being said, the contractor using both doesn't necessarily imply that using both is more effective than either by itself. My current plan is to use both, but I'd like to know if I'm wasting time and money by doing so
    – A.Comer
    Apr 16, 2019 at 14:25
  • Using both was obviously effective up to the time you ended the contract...
    – Solar Mike
    Apr 16, 2019 at 14:38
  • I'm aware that using both worked. I suppose my question is if anyone knows that using both is actually more effective. I'll edit the question to reflect that.
    – A.Comer
    Apr 16, 2019 at 15:10

3 Answers 3


You are just chasing your tail. As long as there is exposed wood and a convenient source of water, you will have carpenter ants.

The solution is to improve your roofing and gutters to keep the house dry.


My understanding (not a pest professional) is that using both negates the effectiveness of the bait. If you kill them before they take the bait home, it does no good.

The idea with bait is to have them take it back and "kill the colony" rather than killing the individual foraging ants as sprays tend to do.

Of course, if you run a pest control company and care more about keeping the business going than eliminating pests, you might choose a method that stops working a week after you stop treating, but charge the customer for two methods, even if one negates the other :-) But I'm a terrible cynic sometimes.

If your infestation includes substantial dry areas you might wish to add insecticidal diatomaceous earth (not the pool version, they are processed differently, as I understand it.) If the area stays dry, you only need to apply it once. It works on a different principle than chemical insecticides, and is supposed to be difficult to become resistant to as a result.

  • This was my initial thought as well, but the spray claims that it is "a non-repellent insecticide that is undetectable to target pests, allowing them touch, ingest and spread the insecticide throughout the entire colony," which makes me think it might be reasonable to use both
    – A.Comer
    Apr 16, 2019 at 17:36

Boric acid is the best consumer treatment, far and away, imho. I'm talking eradication. Look up some recipes to get the bait/poison ratio right and it should be very effective. If you make it too strong, it will quickly knock down the wave, but they will eventually regroup and return.

Unlike sprays, you can use powder to form physical barriers on parts under-attack by dusting the complete surfaces with virtually harmless and fire-retarding boric acid. They simply cannot get to the problem area without getting dosed; it cannot miss!

It's also cheap and safe for kids and pets, which other treatments are not. Some people even eat the stuff as an arthritis cure; I don't really recommend that, but it's pretty harmless to us and ours for what it does to those dang ants!

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