Does Thermacell Work on Flies?

We’ve been using Thermacell for many years now and have covered it on this site numerous times.

However, we never talked about if Thermacell works on flies. The quick answer is it does, sort of.

Thermacell works on most flies, although its effect is not as good as it is on mosquitoes.

Does Thermacell Repel Flies?

You are out hunting or fishing, and you’re getting plagued by black flies or no see ums and wondering how you get rid of these things.

The good news is that Thermacell will repel most flies that bug us when we are out hunting or fishing. 

What Flies Does Thermacell Repel?

Thermacell repels most of the smaller-sized flies. Although it does work on some of the larger flies, in my experience, it is much more efficient with smaller flies like no see ums or black flies.

Black Flies

During my use of Thermacell when out hunting and fishing, I find that it is about 80-90% effective on Black Flies.

Black Flies are right up there with mosquitoes in density and annoyance. Thermacell works extremely well on mosquitoes in the right conditions. 

For black flies, it’s almost just as effective. It seems to me that under perfect conditions, Thermacell will repel both mosquitoes and black flies. 

However, under less than perfect conditions, Thermacell is still good at repelling 90% of mosquitoes, but I find it only repels about 80% of black flies.

No See Ums

Does Thermacell Work on Flies?

These tiny little insects get their name from their size. While their bite is not as irritating as a mosquito or black fly, there are generally more of them.

Another issue with no see ums is that they can get through head nets and window nets.

Fortunately for us, Thermacell works extremely well on no see ums. The great thing about Thermacell and no see ums is that these bugs are only an issue in calm weather, this is also when the Thermacell is most effective.

The only thing worth noting here is that no see ums are fast. As soon as you get out of your truck their on you. This is a problem for about 15 minutes because this is the time it takes for the Thermacell to heat up and start working.

Deer Flies 

Deer flies are one of the worst biting insects in the woods. I find that deer fly bites are much more painful than any other biting insect out in the woods.

I find that deer flies are much more persistent than other flies in the woods and are much harder to deter.

I find that the Thermacell helps to deter deer flies but it’s not completely effective. Usually, a fresh pad will be effective for a while, but it starts losing its affect against deer flies faster than it does against other flies.

Perhaps this is because deer flies are a much bigger, hardier fly than the other flies mentioned.

I would suggest using something like a deer fly patch in conjunction with the Thermacell if deer flies are an issue in your area.


Does Thermacell Work on Flies?

I’ve never had many issues with sand flies out hunting. However, out fishing, sandflies are by far the worst on my list. 

These bugs have bothered me in many rivers or lakes I’ve been fishing and in a number of different countries. It seems like they are everywhere.

Thermacell works on sandflies pretty well. The biggest issue I have with using Thermacell for sandflies is that I find sandflies primarily go for my legs.

This means for the Thermacell to be effective on these flies, you need to place it down low.

Putting the Thermacell down low isn’t an issue, and it will still work for all the other flies and mosquitoes.

The problem is if you’re working your way up or down the bank, it’s awkward and inconvenient.

If you’re wearing rubber boots, you can clip the Thermacell onto it, but you need to keep in mind that it can get warm.

However, the bigger issue is if you are walking through different things like reeds or rushes, you risk damaging the device.

How Does Thermacell Repel Flies

The main chemical in Thermacell is Allethrin. This is a synthetic compound of pyrethrin, which can be found naturally in some flowers.

Allethrin is used effectively in many pesticides to keep flies and other bugs away.

Thermacell uses a mat that is presoaked in this compound. The mat is then placed over a grill that heats up.

When the mat becomes warm, the compound begins to release from the mat, creating a very fine mist.

It is this mist that keeps the flies and mosquitoes away. This is why Thermacell is much more effective on calm days.

During windy days the mist is easily blown away, leaving you unprotected.

Final Thoughts

As a hunter and angler who used to spend a lot of time trying different bug sprays, Thermacell has been one of the greatest additions to my arsenal.

The fact that Thermacell repels most flies in the woods and on the rivers means I don’t need face nets or bug dopes.

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