The Tick and Mosquito Project


Mosquito Dunks and Bits: Our Review

We have often written that the best way to get rid of mosquitoes is to prevent them from ever being alive.  We also know that mosquitoes need water in order to breed, and absolutely love standing water.  What, then, are you to do when you have standing water in your yard, such as a pond or a large puddle that won’t be going away anytime soon?

Mosquito dunks are easy to use for the homeowner and amateur landscaper.

The best thing we have found for cases when you have standing water and cannot easily eliminate it are mosquito dunks, and their cousin, mosquito bits.  These products offer a way for an amateur or a homeowner to easily prevent mosquitoes from breeding, and eliminating their breeding grounds will affect how many mosquitoes are around.  Managing the mosquitoes in your water areas is an important factor in controlling mosquitoes in your yard.

What Are Mosquito Dunks?

Mosquito Dunks (find on Amazon) are a product made chiefly by Summit Chemical.  The dunk is basically a small biscuit-like object that is intended to be put, tossed, or thrown into standing water where mosquitoes are likely present.  The Dunk then dissolves over time, and when it does it releases a chemical that helps control mosquito larvae.  The chemical is actually a type of bacteria that is harmful to mosquitoes but not to other animals. If one Dunk will treat more water than you need (let’s say you just need to control a small water feature) you can always break them into pieces. Our experience is that dry Dunks store very well if in a sealed container.

What are Mosquito Bits?

Mosquito Bits (here on Amazon) are similar to dunks, and also made by Summit.  The Bits release the chemical (same as the Dunks) but more immediately.  The Bits are intended for a more rapid control of known mosquito larvae populations.  The Dunks, on the other hand, are made more for controlling an area over a longer period of time.
Bits and Dunks both are designed to target mosquito larvae, but think of Bits being an on-contact killer whereas Dunks are more of a slow-release method.

How do Dunks and Bits Work?

Because Dunks and Bits are made from the same ingredients, they work similarly.  You put them in the water, and they float and dissolve.  The Dunks dissolve slowly, the Bits more quickly.  The active ingredient, thuringiensis israelensis, is deadly for mosquito larvae.  As the larvae eat it, it becomes a poison to them and will kill them in a few days.  Because it does not hurt full-grown bugs, the impact on the broader food chain is minimal and deemed safe.  As long as he dunks remain in contact with the water, they should work as directed by the manufacturer.

It should be noted that Dunks and Bits are intended for larvae.  If you need to control populations of adult mosquitoes, it is too late for these products.  You will need to find another way, such as a mosquito fog or professional treatment.  There are also ways to keep grown, active mosquitoes away from key living space like patios or swimming pools.  Check out our piece on mosquito killers such as magnets and zappers for more information on the topic.

If you are on top of the problem, though, and attacking the mosquitoes in the spring or where they reproduce, the dunks can be a great option.  Given that 100 years ago, the solution for mosquito larvae was to dump harsh oil and chemicals in to standing water, we have come a long way with safer products like Dunks and Bits!

Note that we have heard several people say dunks and bits also work on

How often do you use Mosquito Dunks or Bits?

mosquito water pond
Sometimes standing water can’t be easily eliminated. That is where Dunks and Bits come in.

Mosquito Dunks are intended to last for about 30 days once in the water.  They are longer-lasting than Bits.  As a result, they are good for water that is likely to host mosquitoes, and that might not go away.  A water feature in a yard, or a pond that holds water throughout the summer are both perfect candidates for the slower-release Dunks.

Mosquito Bits, on the other hand, dissolve more rapidly and are intended to kill the larvae within 24 hours.  The Bits are smaller, and don’t have the time-release feature.  If you know that a pond or puddle likely has larvae, Bits will work faster.  A large puddle that might be the result of a rain storm, but that won’t dry up for a week or two is perfect for the Bits.  More extended-release needs are better-served by the Dunks.

Are Mosquito Dunks and Bits safe?

According to the manufacturer, Mosquito Dunks and Mosquito Bits are only harmful to mosquitoes and their larvae.  The manufacturer cites that they are not harmful to humans or pets.  The main effect on animals, according to Summit, is that they would get a large dose of calcium and protein.

Furthermore, the CDC has found that Bti, an active ingredient in Dunks, are not harmful for humans, animals, or honeybees.  Bti is naturally occurring, and found in soil.

We have no reason to doubt Summit on its claims.  The World Health Organization cites that the bacterium used in Dunks and Bits is generally regarded as safe in natural applications as well as in drinking water.  With that said, we are not pathologists or biologists so cannot be the authority, but this product sure seems safe as advertised.

What are the alternatives to Mosquito Dunks and Bits?

There are stronger larvaecides and insecticides that can be applied, but they are not all as nature-friendly so we would only suggest using them in extreme cases, and under the direction of a professional.  While fogging is generally viewed as safe (because the chemicals are so diluted) we tend to prefer Bits or Dunks.

Larvae prefer standing water, so one option is to make sure that the water has some level of movement.  This is easier said than done if you are dealing with a natural pond, but if you have a water feature you might be able to install a mechanism to keep the water moving.

Of course, the best option of all is to eliminate standing water from your environment.  Removing water is among the most nature-friendly and organic solutions to the mosquito problem, and one that gets at its root cause.  This is easy to do if we are talking about gutter backups, small puddles, or clogged runoff drains.  In the case of a water feature or larger natural pond, Dunks and Bits can be an excellent choice.

Maybe the right way to think about bits and dunks is not as an either / or with other methods, but alongside other methods.  If you really want to get rid of mosquitoes in your yard or acreage, the combination of a good yard mosquito repellent alongside bits and dunks can be very effective.  If you are trying to control mosquitoes in a smaller area, then consider a fogger. Just use them all as directed by the manufacturer.

Can You Make Your Own Mosquito Dunks and Bits?

We don’t recommend it.  The ingredients for Mosquito Dunks and Bits something called Bacillus thuringiensis subspecies israelensis, or B.t.i. for short.  It is a naturally-occurring larvacide, but just because it is naturally-occurring does not mean it is safe for the layperson to handle or mix.  Even snake venom is naturally-occurring!  Unlike tick tubes, which can be homemade pretty easily, Mosquito Dunks should be purchased in a store so you can allow the professionals to process and manufacture the product for you.  (you can find them here).

When do I use Mosquito Bits and Dunks?

This is an important question.  The time to use mosquito bits and dunks is different for the two products.  Both are intended to treat the breeding ground for future mosquitoes, though.  Neither is supposed to kill adult, active mosquitoes.  These are to ward off the larvae.  If you kill all the larvae, you win the war!

Mosquito bits are fast-acting but don’t last as long.  Use this if you are worried about an impending mosquito problem and can stay on stop of the area you are treating.

Mosquito dunks, on the other hand, work more slowly, but last a lot longer.  I like to use these on some recreational acreage I own, when I know I might not be back for a month at a time.

Both are effective, but for different situations.

Where should I use Mosquito Bits and Dunks?

Stagnant water.  Mosquitoes really dislike oxygenated water, which means that running water that is collecting oxygen along the way (think of a mountain stream with rapids and whitewater) is not the problem.  Rather, the problem is slow-moving or stagnant water that is not moving.  That water tends to have very low oxygen, which is exactly what mosquitoes want.

This means that ponds, swamps, certain landscape water features, and other areas with water that won’t move around much is where you need to target.  Of course, if you can get rid of the water first (such as dumping out an old bucket full of water, or used tires collecting rainwater) do it.  For the water you can’t get rid of, you then use the Bits and Dunks.

I personally have an old farm where I often only visit every 4-5 weeks. In the times I am away, old tires and used oil drums tend to fill up with rain water. I leave a dunk in these likely water catchments while I am away, and definitely notice that the mosquito populations are lower when I visit the next time.  You can even throw one in a big puddle, the kind of puddle that might not dry up for 2 weeks, and it will make a dent in your skeeter population.

Is it true that they work on gnats and fungus gnats?

fungus gnat dunk bit
The fungus gnat

While dunks and bits are designed for mosquito control, we have heard of people having good success using them for fungus gnats.  These are the gnats that annoy people all over the country, mainly in the summer months.  If you find a breeding ground for the gnats, likely anywhere there is fungus as their name implies.  They typically thrive in moist soil that is rich in organic matter and tends to not drain quickly.  Because you don’t have a puddle or pond to throw the dunks in to, we’ve heard that it works to dilute the dunk in a bucket of water, and then lightly spray or pour the treated water on the problem soil.

Where do I get them?

Dunks and Bits are available at many hardware and home improvement stores, but we have access to them at great prices from Amazon.  They come in several sizes.  As with anything, the more you purchase, the lower your per-unit cost becomes.

Our Mosquito Dunks Field Test

We field tested the Dunks in a backyard pond that we always felt was a mosquito breeding ground.  This pond would be deepest in Spring, and usually dry up by August.  Those two or three months were plenty long to host several mosquito hatches.

The Dunks themselves were very easy to administer.  Take them out of the package, and put them in the water so they float.  We noticed that by setting them on the water’s edge, they tended to get caught in mud and weeds, so we tossed them a few feet into the middle of the water.  Wind will no doubt move them around, but as long as the Dunks were in contact with the main body of water, we felt they were doing their job.

The hard part is knowing exactly what the effect was, because this was not a controlled experiment for a few reasons:

  1. We were using the Dunks, but our neighbors were not. Mosquitoes do not respect property lines, so we could control our mosquitoes but that didn’t mean our neighbors’ mosquitoes didn’t just take their place.
  2. It is impossible to know what to compare a mosquito population to. Some years are better and worse than others.  Just because there were still some mosquitoes, we had no scientific way of knowing if we had fewer than we would have without the dunks.
  3. We are generally pretty good about keeping our area mosquito-unfriendly, by keeping the grass down, eliminating standing water, and taking other measures to control mosquitoes.

With all that said, we think this is a very good product, and one that should be used more for homeowner mosquito control.  It is easy to administer for a homeowner, without any advanced skill in the pest-control area.  It sure seems safe as advertised.  It is much easier than trying to drain a pond, something that isn’t really feasible in our case.  We think that there was a positive impact from the Dunks, and we think if several homeowners in a neighborhood used them during the same season, the impact could be quite noticeable.

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