Mosquitoes are annoying, but they make for an amazing source of income. Companies and individuals alike profit off the hatred that exists for mosquitoes, selling products that claim to repel or kill mosquitoes with efficiency and ease.

However, it can be hard to tell which of these products work and which ones merely act as a placebo of sorts, so shopping for the perfect solution to your mosquito problem can be more of a hassle than you bargained for.

With this article, I want to examine Summit’s trademarked Mosquito Dunks, a larvicide dedicated to killing off mosquito larvae before they can bite you.

What is Summit?

Located in Maryland, Summit Chemical Company has spent over 50 years in the manufacturing industry, though it wasn’t until the mid-70’s/early 80’s that the company truly hit their stride with the creation of their mosquito Dunk larvicides.

Summit offers many different forms of insecticides and larvicides, especially their Mosquito Bits product line, but for now let’s focus on their Dunks line and what that’s all about.

What are Mosquito Dunks?

Summit Chemical Co. invented the mosquito Dunk in the 1980s as a mosquito control solution that didn’t require the user spraying their whole house with a can of RAID or dealing with adult mosquitoes.

When it comes to appearance, a mosquito Dunk looks somewhat like a rotten Lifesaver candy. Having said that, you shouldn’t eat one, though if you or your pet does end up eating one, it’s ok; Summit claims mosquito Dunks are harmless to everything besides mosquito larvae.

Is this true? The short answer is yes, mosquito Dunks are completely harmless to people, pets, and any form of wildlife that isn’t a mosquito.  This claim is 100% guaranteed by the CDC, writing that a mosquito Dunk “is not toxic to people. It has not been shown to make people sick.” Additionally, The EPA has registered Mosquito Dunks for use in animal water troughs and fish habitats.

This safety is due to the main ingredient in Summit’s Dunks: a bacterium known as Bacillus thuringiensis israelensis, otherwise known as B.T.I. T

This one ingredient is the lifeblood of mosquito Dunks that guarantee success, but how?

What is B.T.I.?

Bacillus thuringiensis is a bacterium, with israelensis being the specific strain Dunks use to kill the larvae (Fun fact, the strain name is based off Israel, where the strain was discovered. This kills mosquito larvae and offers a pest control method that’s safe to use in your water garden.

B.T.I. is a popular bacterium for larvicides, with it being used in many states for aerial spraying, water spraying and various other forms of treatment. As of now, it remains one of the best methods of killing larvae, due to its non-toxic nature to people or wildlife.

How Do They Work?

Similar to how DEET makes commercial mosquito repellents effective, BTI guarantees the effectiveness of using a mosquito Dunk.

However, mosquito Dunks aren’t effective against adult mosquitoes; Dunks only work against mosquito larvae. This is due to the nature of B.T.I and the way mosquito Dunks are used.

See, female mosquitoes lay their eggs in water, shallow or deep. Mosquitoes don’t discriminate between bodies of water either, meaning your pool or pond run the risk of becoming the breeding ground of choice for mosquitoes.

If you’re unlucky enough to become a victim of mosquito breeding, mosquito Dunks remain a viable solution. When placed in a body of water, the Dunk will slowly release B.T.I over the course of 30 days. As mosquito larvae hatch and look seek out sources of food, they’ll consume the B.T.I., killing them, as B.T.I. is harmful to mosquito larvae and larvae only, which is why adult mosquitoes remain unharmed by the use of B.T.I.

How Do You Use Them?

Using a mosquito Dunk is as simple as the ABCs. Simply let the mosquito Dunk float in the body of standing water housing the mosquito larvae. After that, all you need to do is let the Dunk kill of the larvae, solving your infestation at the source. They target mosquito populations, fungus gnats, and other various subspecies, and are known to be very effective.

However, there are a few specifications that are important to the use of these Dunks, so let’s go over them real quick.

Where To Use Them

Just like mosquitoes, Dunks don’t discriminate between any body of water, the only requirement being that the body of water must be constant; it can’t dry up, as that would leave the Dunk ineffective. This makes them great for rain barrels, bird baths, flower pots, tree holes, or swimming pools.

That said, if the affected body of water tends to splash around or leak, you can anchor the Dunk to something like a stake. This ensures the Dunk stays in the body of water without breaking it up and limiting its effectiveness.

Also, Summit mosquito Dunks won’t be as effective in swamp waters, water found around dumpsters or any body of water filled to the brim with organic material. In these cases, mosquito Bits will work in place of Dunks.

When To Use Them

I want to reiterate the fact that mosquito Dunks only work against larvae. Grown mosquitoes will not be affected by a mosquito Dunk. So, use Dunks only when you are aware of nearby bodies of water being used as larvae breeding grounds.

Yes, you’ll still have to use repellents and traps for the adult mosquitoes that are around, but at least you won’t need to worry about more being born.

How Many To Use

Mosquito Dunks are sold in packs of two, six and twenty. However, you don’t need to use a whole Dunk per body of water. In the same vein, a whole Dunk may not be enough to cover the whole body of water effectively.

A good rule of thumb is to use ¼ of a Dunk for 5 square feet of water, ½ of a Dunk for 5 to 25 square feet, and a whole Dunk for 25+ square feet. Take note that a whole Dunk contains only enough B.T.I. to cover 100 square feet of water; if the affected body of water is over 100 square feet, you’ll need more than one Dunk. Lucky for you, Dunks don’t expire, so a pack of 20 can last you years.

Though if you need to clear a large body of water of mosquitoes, you’re better off using other products, such as Microbe-Lift BMC’s concentrated liquid formula, as that will cover a much bigger area than a Dunk will. However, there’s nothing preventing you from using multiple Dunks, just be sure you’re spreading them out in an even fashion.

Are They Effective?

Here’s the real question: are mosquito Dunks effective? Fortunately, yes!

B.T.I. does an excellent job killing off mosquito larvae over the 30-day period they take to expire, if not a bit too slow. By that, I’m referencing the fact that Dunks may be too slow-paced to kill larvae already on their way to becoming adults. However, for most larvae, the Dunks will work just fine.

Don’t believe me? Just take a look at a few of these reviews:

“Nice because it keeps working. Crumble them up the first time to kill quick at the start of summer, then add whole ones in a couple weeks, and once a month after that.”

“They say one for 100 square feet but just putting one in the middle doesn’t work as well. Break it up and put it in two or three places. Easier to break after it’s wet.”

“This is the only thing I could find that’s truly safe for my lily and fish pond. Still have fish, dragonflies, butterflies, frogs, turtles, all the other life, but no more mosquitoes.”

“They’re supposed to last 30 days but they don’t seem to last that long.”

“The neighbors didn’t empty their pool when they moved out. Noticed more mosquitoes in the backyards a few weeks later. Somehow two of these Dunks just happened to get tossed over the fence into it. Mosquito level slowly getting back to normal but wish we’d done it before the first batch hatched.”

“We use half a Dunk in each rain barrel. The water is for the garden, and I was hoping it would kill some of the garden pests too but I guess it’s just for mosquitoes. Still, the rain barrels are clear of larvae and it doesn’t seem to harm the worms that are good for the garden.”

“Doesn’t do anything for adult mosquitoes. Good for killing larvae, but you still need repellent or something for the adults that come in. Wish all the neighbors used them.”

Are They Worth Using?

When compared to other larvicides, Dunks are undoubtedly worth using, though it all depends on your situation. If the larvae are being bred in a small or medium-sized body of water that is at a standstill most of the time, a Dunk is one of the best products you can use.

However, as I mentioned earlier, you may want to use Summit’s Bits if the affected area is large or in a hard-to-reach place, such as in a bush or in the crevice of a tree.

How Long Do Dunks Take to Work?

Once put into the water, the Dunk will start releasing B.T.I. a few hours after initial application. From then on, the Dunks will continue to release the bacteria for 30 days. After the 30 days, you will either need to replace the Dunk or add a new type of larvicide; whichever you prefer.

Take note of the speed at which Dunks release the bacteria; since it is slower-paced, some larvae may be able to grow and escape before they’re killed, which is why adding Summit’s Bits two weeks out is recommended before adding Dunks.

Will the Dunks Expire?

There’s conflicting information when it comes to the expiration time of mosquito Dunks. Summit’s website claims that their Dunks lack an expiration date, as B.T.I is not a living bacteria, therefore there’s no way for it to expire. In these claims, they point out tests done by government associations that used 8-year old Dunks and theys till worked perfectly, however I was not able to locate these tests.

On the flip side, some sites say Dunks should be replaced every 2 years, though these claims are also unfounded. As of writing this, I find it better to side with what the company’s official FAQ says, so count on your Dunks lasting a minimum of 8 years.

How Expensive are Dunks?

Summit sells their Dunks in packages of 2, 6, 12 and 20. As with most products, the lowest count, in this case, the 2-count, will be more expensive per Dunk, and the highest count, the 20-count, will be the cheapest per Dunk. That said, we’ve already established that Dunks don’t expire, so don’t think you need to purchase more than you need.

A 20-pack of Dunks will set you back $20, a 2-count around $5, and the 6 and 12 counts will cost somewhere in the $10-$15 range, but this all depends on where you’re buying them from.

Rating Dunks

It’s time to put together all the information we have and rate Dunks on a grading scale akin to your old high school. Our rating will focus on 3 features:

  • Efficiency/Effectiveness = 35%
  • Price = 25%
  • Ease of Use = 25%
  • Safety = 15%

Efficiency/Effectiveness = 9.5/10

There’s no question about the effectiveness of a well-placed Dunk. In the field of larvicides, it’s one of the best options you have for you nasty mosquito problem.

Lasting a whole month before a new one is needed, Dunks spend that time well, killing off any larvae that may exist in your water. The only gripe I have is the ability for larvae to escape before the Dunk starts working. However, that’s less the fault of the product than it is poor timing.

All this said, the Dunk is worthy of a 9.5/10. It’s not perfect, but it’s close.

Price = 10/10

Though a 20-pack of Dunks may cost you $20, those Dunks will last you 20 months minimum, assuming you’re using one whole Dunk. However, since you can break up a Dunk into pieces, they can last much longer-years in fact.

The product is definitely worth the price, giving our Price rating an easy 10/10.

Ease of Use = 9.5/10

There’s little guesswork involved when using a Dunk. Sure, you may need to figure if you truly need to use a full Dunk, but that’s it. Once you’ve figured out how much you need to use, you break it apart and throw in the water.

From there, you don’t need to do anything else. Overall, Dunks are a 9.5/10 when it comes to ease of use.

Safety = 10/10

There’s not much to say here; Summit has succeeded in producing a 100% safe larvicide that poses no harm to you or your pets. Even tadpoles could end up eating the dunk and they’ll still grow up to be great frogs. Easily a 10/10.

Overall Grade = 97% (A+)


Q: What are mosquito Dunks made of?

A: Mosquito Dunks are a donut-shaped capsule filled with B.T.I., the active ingredient responsible for killing the mosquito larvae.

Q: Will my mosquito Dunks expire?

A: Summit Co. claims no expiration date for their Dunks due to B.T.I. not being able to expire (this because B.T.I is not a living bacteria). So no, your mosquito Dunks can last as long as you need them to.

Q: How long will one mosquito Dunk last once used?

A: Once put in water, the Dunk, or piece of, will last 30 days. After that, if not all the larvae are gone, you’ll need to put another Dunk in and wait another 30 days.

Q: What will happen if my pet eats one?

A: Absolutely nothing! B.T.I. is harmless to every living being except mosquito larvae, so your dog will only notice the extra protein it’s eaten.

Q: How do I store mosquito Dunks?

A: Summit recommends a well-ventilated storing area for their Dunks, though extreme cold will not reduce the product’s effectiveness. However, with B.T.I. being a bacteria and all, prolonged exposure to heat may hurt the product’s effectiveness.

Q: Where can I use mosquito Dunks?

A: You can use them in any body of water where larvae reside, as long as the body of water is not dirty or infested with other organic material; in this case, Bits will need to be used in place of Dunks.

Q: What if I need to cover a large body of water?

A: Summit actually makes another larvae killer called mosquito “Bits”, which are made to cover large bodies of water. However, one Dunk is only good for up to 100 square feet of water.

Q: How much are mosquito Dunks?

A: A 20-pack of mosquito Dunks will set you back by around $20, give or take one or two dollars. A 2-pack on the other hand will cost around $5, and the 6 and 12 packs will cost in between those two.

Q: What species will Dunks work against?

A: Summit claims their mosquito Dunks work against all 2,000 species of mosquito larvae, so there’s no need to worry about the Dunk’s effectiveness.

Q: Will Dunks kill adult mosquitoes?

A: As nice as that would be, Dunks unfortunately remain harmless against adult mosquitoes, as B.T.I. is harmless against everything but larvae.

Q: Where can I buy mosquito Dunks?

A: You can buy them from most stores and online retailers, such as Amazon or Home Depot.