Do Mosquito Bits and Dunks Work? Are They Safe? A Review

It’s the first nice day of the season. You’re sitting down for a meal outside with the family.

Suddenly that annoying buzzing around your ears. Then, a pin prick. Your hand swats wildly *SMACK*, but nope. The skeeter beat you. You look down and there it is: a giant, red, itchy welt.

The fresh joy of being outside basking in the Spring sun just became tainted. It’s mosquito season.

There´s something else this incident informs you about.

You are too late.

Late with taking precautions. Preparing your yard to reduce mosquito infestation.

Founding Father Benjamin Franklin already said it, “An ounce of prevention is worth a pound of cure.”

Which certainly goes for those vicious bloodsucking gits.

You have heard about Mosquito Bits and Dunks before. While scratching your welt you wonder,

Do they work?

This is a legit question. If you have a really large yard you will be spending about 30 bucks a month so it better be worth it and work. Of course, for medium or small sized yards costs are much lower.

Does this larvicide really have to ability to kill mosquito larvae?

To keep it plain and simple, yes, Bits and Dunks really work.

EPA has this to say:

“Killing mosquito larvae with microbial larvicides before they emerge as adults can reduce or eliminate the need for ground or aerial application of pesticides to kill adult mosquitoes.

It should be noted that how long and well they work depends mainly on “the mosquito species, the environmental conditions, the formulation of the product, and water quality”.

What exactly are mosquito dunks and bits?

Mosquito Dunks and Mosquito Bits are made from naturally occurring soil bacteria called Bacillus thuringiensis strain israelensis (for the rest of us: Bti).

They are one of the most effective products on the market today.

You may be familiar with Bt products as a common form of pest control originating in the early 1900s. Bt biocontrol products are often used on agricultural and garden pests, such as

  • Btk on caterpillars and
  • Btt on beetles.
  • Bti is simply a different strain of Bt that only affects mosquitoes and black flies. (it’s very specific in its larvicidal activity)

Since Bti occurs naturally in the environment, it is considered an all-natural biological control product. Dunks and bits are produced by harvesting Bti from soil, then inactivating the bacteria with enzymes.

The inactivated bacteria is added to fillers and packed neatly into dry briquettes or pellets. By the time it is sold to the consumer, it is no longer a living bacteria, however it is still just as effective in killing mosquito larvae.

How do they work?

When eaten by a mosquito larvae, “toxic crystals” form which travel to the stomach and enter the stomach cells. The crystals cause the stomach cells to explode, forcing the mosquito larva to stop feeding until it starves to death.

It can take several days for all of the mosquito larvae to die, so if you see no immediate results, don’t be alarmed.

Don’t fret if there still appear mosquitoes upon treatment

Older mosquito larvae tend to stop eating as they approach the next life stage, therefore Bti may not be as effective on older larvae and some adult mosquitoes may emerge after the initial Bti treatment.

Bti vs Bs – Bacillus thuringiensis israelensis vs Bacillus sphaericus

A similar product to Bti is Bacillus sphaericus (Bs) which is another bacterial biological control product.

The difference between Bti and Bs is that Bti products contain dead bacteria, whereas Bs products contain live bacteria.

Bs downsides:

  • Bs may not be as effective on certain species of mosquitoes.
  • Another disadvantage, there has been some recent concern about Bs insecticide resistance in populations of disease-carrying mosquitoes.

Studies indicate it appears to be less effective in killing the Aedes species

Most mosquito control products purchased by homeowners contain Bti, however Bs is an additional mosquito control option.

Dunks vs. Bits, when to use which?

Bti products come in several formulations, including donuts and briquettes (collectively known as dunks), and granules or pellets (bits).

Main difference:

  • Dunks last longer. They dissolve slowly and have a time-release feature.
  • Bits work more work quickly. Need to be applied more often but offer quick results.

Mosquito Dunks

Dunks contain slow-release formulas, meaning they will last approximately 30 days in the water.

Dunks float on top of the water, and as the mosquito larvae naturally feed, the Bti is consumed.

  • These are useful in open bodies of water such as vacant pools, and can be broken up to treat smaller surface areas.

Mosquito Bits

Bits are, in Bti coated, corn cob granules. Bits are a quick-release formula, and therefore only last approximately 7-14 days based on the formulation.

Unlike dunks, bits will sink to the bottom of the water once waterlogged.

  • Bit formulations are more useful for smaller, hard to reach locations such as tree holes, or large bodies of standing water, such as flooded crop fields and marshes.
  • In areas with aquatic vegetation, such as water gardens, marshes, or flooded orchards, the bit formulation may be more useful since their smaller size can penetrate in between and underneath vegetation.
  • In addition, they can be dispersed more evenly in water with little movement. They can also be added to dry ground if large amounts of rain are expected and the area doesn’t drain well.
  • However UV sunlight will degrade Bti quickly, so leaving them exposed to sunlight for periods of time will decrease their effectiveness.
  • When using bits in ponds, it is important to remember that fish and turtles love to consume anything pellet-like, including your mosquito bits.

While bits are completely safe for wildlife, eaten bits mean less Bti for the mosquitoes to consume. There is another product called mosquito plunks which are simply bits packed into a water soluble bag.

Update: “The Mosquito Beater WSP (formerly Plunks) is a water soluble packet containing BTI granules, essentially identical to Mosquito Bits”.

The bag prevents munching from pond inhabitants, but should be tied down as bags tend to float around, sometimes causing uneven dispersal of the Bti. Alternately, you can make your own Plunks/ Mosquito Beaters by adding Bits to a stocking.

Are Mosquito Bits & Dunks Safe?

The best part about Bti products (aside from no mosquitoes, of course) is their environmental safety. They are deemed organic by the USEPA.

The Bti bacteria affect mosquitoes and black flies only, both of which are vicious biters.

When used properly, these products are safe to use around homes with children, pets, and wildlife. They can safely be used in fish ponds and horse troughs. They are even safe for other beneficial critters such as honey bees, dragonflies, and tadpoles.

We get it, you can’t be careful enough. Therefore we have consulted experts for their opinion on specific safety issues. Here are the most common FAQ;

  • Q: Do mosquito bits / dunks kill tadpoles?
  • A: No they will not hurt tadpoles. The Bt in mosquito dunks and bits kills mosquitoes and a few related insects only.
  • Q: Do mosquito bits / dunks  kill fungus gnats?
  • A: Recent government requirements for reporting info on insecticides by manufacturers conclude that BTi affects mosquito larva, fungus gnat larva and blackfly larva. It may have an effect on daphne but numbers are too low to be included in the data.
  • Q: Do mosquito bits / dunks kill dragonflies?
  • A: There are no indications dragonfly larvae are affected.
  • Q: Do mosquito bits / dunks harm bees?
  • A: Bacillus thuringiensis subspecies Israelensis strain EG2215 does not harm bees. It is designed to kill mosquitoes and a limited amount of  related, aquatic insects only. These include fly larvae and midges.
  • What if my cat or dog eats from the Bits or Dunks? Does that harm them?
  • No, according to the manufacturers they are completely harmless, “If an animal eats a Mosquito Dunk or drinks water treated with a Mosquito Dunk, it essentially gets a large dose of protein and calcium.” 

Keep an eye out though because your dog may like to eat them, rendering your pest-control efforts fruitless. Crumble the Bti product well or place it out of reach of pets, squirrels and raccoons.

Also important, Bti is harmless to mosquito predators too.

Concluding: The only ones who aren’t safe are the mosquito larvae and you if you don’t take action and use Bti to control the pest around your living area.

Note: Although the israelensis strain anti pest activity is  very limited,  certain types of non-biting midges, which serve as food for fish and wildlife,  may be affected.

How long do they work?

Many Bti products last up to 30 days in the water, but always read the label to determine when to re-treat.

As mentioned previously, fish and turtles love to eat anything shaped like a pellet, so if using bits in ponds, be sure to secure the bits in a water-permeable stocking or purchase mosquito plunks.

Mosquito Bits and Dunks Reviews

“We live among muddy and constantly swampy areas and Mosquito Bits worked like a charm. We broadcasted the product in still water and over the mud (we found the dunks too compacted to work).  Because it’s easier to cover large areas, Bits turned out far less expensive to use.”

Dunks are a lifesaver, we have almost no mosquitoes and it’s completely safe for our lily and fish pond. Our fish, butterflies, dragonflies, turtles, and frogs flourish and we can enjoy them without the flying pests”

“Tossed it in and the day after I could skim off all the dead larvae.”

How to use Mosquito Bits and Dunks

In order to optimize mosquito prevention, we must first understand the mosquito life cycle.

Mosquitoes start their life in water, which begins when a female lays her eggs on the water. The eggs hatch into mosquito larvae, which feed and grow for several days.

At the end of the larval stage, mosquitoes pupate (much like a butterfly) before they hatch and fly away as the annoying needles with wings.

Different types of mosquitoes prefer different water conditions, but those that live and bite around homes usually prefer small amounts of stinky, stagnant water.

  • Some of the most common skeeter breeding habitats are unfiltered bird baths, clogged gutters, flower pot saucers, French drains, wheelbarrows, etc.

Most breeding spots can be remedied by simply dumping out water once a week, however sometimes conditions ask for more thorough measures in the form of “biological control”.

If it holds water, it will breed mosquitoes.


Where to use Bits and Dunks

Certain spots such as bird baths or the rain barrel are obvious. Pay special attention to the following areas:

  • Muddy areas after rain. Anywhere that gets mushy or swampy. In deeper garden beds, in some areas of soil that don’t drain as quickly in the yard/garden.
  • Water gardens, flower pots, old automobile tires, rain gutters, decorative ponds, ditches, roof gutters, drainage gulley, Koi ponds, hydroponic systems, animal water troughs,  livestock water, rain barrels.
  • Under hostas, earth boxes, in tree holes, evergreens, in ivy, pachysandra, in the patio drain, by the fence line.
  • Generally, mosquitoes tend to breed under wet, shady tree and foliage areas. They may even be located near mosquito repelling plants.
  • Shady areas, depressions in the grass, tree stumps and tree crotches, grass, mulch, planters or garden tools and wherever else water accumulates.
  • Make sure to use them indoors as well (if necessary). Treat flower vases, flooded basements, building foundations, indoor fountains and other areas as well. Mosquitoes will breed there just as happily.

Tip: If you use Bits, using a canister with a shake top lets you walk around the premises while the canister bangs against your leg spreading the stuff effortlessly.

“Our neighbors moved out but didn’t empty their pool. Mosquito mayhem in the backyard was the result the following weeks. We threw a few dunks over the fence into the pool. This helped diminish the skeeter plague within a few weeks.”

Quick and dirty tips for successful use

The war on the flying bugs requires the scorched earth strategy. Or the mosquito version actually. Leave no area untreated, give them no chance to breed nor hatch.

  • 1. Start treating in time. Larvae start growing early so depending on where you live, start using the dunks in April, early March or even February

If you know rain is expected, or you know of areas that consistently hold water, apply Bti before mosquitoes become a problem.

No mosquito larvae = no mosquito bites (or at least much less). Treatment before or just after eggs are laid will yield the most success.

  • 2. Reapply as needed. Dunks last approximately 30 days, but bits only last 7-14 days. Reapplying at correct intervals will ensure no mosquitoes develop in between applications.
  • 3. Apply according to label instructions. One dunk will treat approximately 3 square meters of surface area (about the size of a hot tub), but bits will be applied differently depending on the environment. It is important to treat enough so that mosquitoes don’t develop, but over-treating can be a waste of resources and money.
  • 4. Think outside the box. Birdbaths, vacant pools, and gutters are all obvious mosquito breeding habitats. However, there may be a frisbee hidden under a bush, a broken sprinkler head hidden in the garden, or a low lying area underneath your flower beds. Make sure to examine your environment with a fine tooth comb and treat every possible breeding location. Mosquitoes will lay eggs in as little as 1 tablespoon of water.
  • 5. Involve your neighbors. Your yard can be as dry as the desert, but if your neighbor is breeding mosquitoes, you are still on the dinner menu. Share your new found mosquito knowledge with your neighbors, or group together and purchase in bulk so everyone can treat. (you could buy some extra and give it to you direct neigbors, they may or may not use it and even reimburse you but chances are you will enhance mosquito control in near your home).

“Doesn’t kill flying mosquitoes. Adults still come flying in (although less). Would be great if the whole neighborhood used this.”

Treating with dunks and bits is only one step in personal mosquito protection. For the best results, follow the 4D’s of mosquito prevention:

  • Drain standing water,
  • Dress in long sleeves and pants to prevent skin exposure, and
  • Defend yourself with an EPA-approved mosquito repellent.
  • Destroy the pesky bugs, their larvae, and their breeding grounds

Typical measures to protect against mosquitoes include nets, traps, personal repellents, fogging, and so fort. Especially since Bits and Dunks do not kill adult skeeters.

Mosquito dunks and bits, however, are an integral part of such a multi-modal approach.

How much Bits, Dunks, or Plunks do I need?


Just like Dunks, Plunks need to be replaced every 2 weeks. Add one Plunk per 50 square feet of water surface.


You will need about 1 Dunk for every 100 square feet. To spread them evenly and thus maximize their effect, throw Dunks 10 feet from each other.

Break Dunks up for smaller areas. The manufacturer recommends:

  • 1/4 Dunk – up to 5 square feet of water
  • 1/2 Dunk – 5 to 25 square feet
  • 1 Dunk – 25 to 100 square feet

Tip: Buy in bulk. Twenty packs are much cheaper per unit than two-packs. They stay effective for at least 8 years to come so the next few mosquito seasons you are well-prepared.


  • One teaspoon of Bits is recommended for every 25 square feet.
  • Or use one tablespoon for every 75 square feet.
  • Use a half cup for every 600 square feet.

Bits are available in 8 ounce and 30 ounce packages.

  • The 8-ounce container is good for roughly 2,178 square feet (contains about 87 teaspoons or 29 tablespoons).
  • The 30-ounce container has enough bits for over 8000 square feet (contains over 300 teaspoons or 100 tablespoons).

The same principle goes here, larger packages are much cheaper. The 30 ounce package will save you about half the costs.

Which brand to choose?

Several brands exist, however a couple of the most popular brands are Mosquito Dunks® and Mosquito Bits® by Summit Chemical.

Other brands are Plunks,  Gnatrol, Vactimos, Bonide’s Mosquito Beater WSP (Water Soluble Pouch).

Some liquid ready-to-use formulations are now also on the market, such as:

  • Liquid BMC. Vectobac is a liquid formulation commonly used in commercial mosquito control operations.
  • Microbe-Lift BMC (Biological Mosquito Control) is another liquid formula.

Liquid products may require dilution and a sprayer, which makes them not generally recommended for homeowner use.

Microbe Lift BMC is an exception though. This product is very easily applicable.

“I swear by Microbe Lift BMC. I use the measuring cup for large bodies of water and an eyedropper for the birdbath, the dog’s wading pool and so on. “

“Liquid Bti is discrete since it doesn’t show. Dunks and Bits ruin my view, floating in the pool and ornamental water garden. Great for puddles and ditches but when esthetics are important, I use Lift BMC”

No matter what formulation you choose, it is important to remember that all treatment options should be registered and approved by the EPA. Using a non-EPA approved product carries the risk of hurting the environment and the user.

Labels will always tell you what your active ingredient is (look for Bti), how much to use, how to properly apply, and when to re-treat the area.

Plunks reviews

“Basically Dunks in a pouch. Work quickly in killing larvae but don’t last as long as Dunks. Plunks are pre-measured in a dissolvable pouch you just throw in the middle of the pond”

“Great stuff, highly recommended. There’s no annoying scent, no nasty fog, no buzzing UV light traps with heaps of dead insects, just toss them in the water and you’re set for two weeks.”

Where to buy?

Now you may be thinking, “These sound great, but where do I buy some?” You are right, they are effective means to control a mosquito problem and you should get some.

Bti products are available at most big box stores and online.

  • You can buy dunks in small 2-packs, or purchase them wholesale with up to 20 dunks per pack. Or order them online. Get a Summit 20 pack Mosquito Dunks to cover 2000 square feet.

By using these mosquito control products as instructed and regularly you will be able to reduce the nuisance and protect your health.

You may still have to use DEET or a bug zapper for complete safety but Bits, Dunks, Plunks and Microbe Lift BMC go a long way in taking back your yard.

Happy mosquito hunting!


Source: Williamson County and Cities Health District.

24 thoughts on “Do Mosquito Bits and Dunks Work? Are They Safe? A Review

  1. Is it safe to use on vegetable seedlings/sprouts that humans will eventually eat?? I have a fungus gnat problem with my indoor plants!

    1. I just found this in the Summit Mosquito Dunks FAQs as I was trying to find this answer, too:

      Are Mosquito Dunks® safe to use around fish,
      birds, wildlife, pets and children?

      Yes. B.t.i., the active ingredient in Mosquito Dunks®, is very
      target specific for mosquitoes and does not adversely affect other
      organisms in the water. Mosquito Dunks® are also safe for use
      around birds, wildlife, children and pets. The EPA has registered
      Mosquito Dunks® for use in animal watering troughs and fish
      habitats. More recently the Dunks® have been approved for use
      Organic Production and Gardening, under the National Organic
      Program guidelines.

    2. Hi, did anyone answer that question from Carolyn? I also want to use it on herbs with fungus gnat infestation but not sure if this is safe???

  2. The Mosquito Dunks and “Plunks” a name that is discontinued due to it infringement on the trademarked Dunks, are not equal products. The Dunks last up to thirty days and sometimes longer depending on environmental conditions. The Mosquito Beater WSP (fromerly Plunks) is a water soluble packet containing BTI granules, essentially identical to Mosquito Bits. So your answer equating the Dunks and other product is technically incorrect.
    Thanks for all your great info and please let Summit know if you have any questions,
    Zach Cohen
    Vice President
    Summit Chemical Company

  3. I used thextensively bits on areas around my house and it did seem to kill mosquito larvae. But it seems to feed thesee horrendous looking worms in the water. Not sure if they are hookworms of something. They’re scary looking from there massive swarm I Nguyen over the bits. They aren’t phased by the bits and not only love them but seem to be growing. I don’t have a clue what theyou are. But I’ve been taking video every day or two. So I don’t know which is worse, mosquitos, or whatever the heck those are and what possible danger they may hold to pets, children, and ourselves. If you would like to see videos post and I’ll YouTube them

  4. I bought this product to try and it is great. We have been getting a lot of rain in Southeast Texas lately. I had a 5 gallon bucket about 3/4 full. It was full of mosquito larvae. I added about a teaspoon in the bucket and they died instantly. I watched them cover the bottom of the bucket and within seconds they squiggled to the top of the bucket. By the time they got to the top they were dead. I added to the trays under my outside potted plants and instant death. What I didn’t know was the dogs were going out and drinking the standing water in them. When my wife told me they liked drinking outside more than out of their water bowl I panicked. But to my surprise it did not phase them at all. So now I don’t worry about it and it still has not affected them. They have annual tests at the vets and they were found in perfect health. Blood test came back normal. For what it cost which isn’t much for how it works I will continue using it.

  5. Is there a shelf-life or expiration date for the Bits? I.e., if I purchase a large container for economy and don’t use it all this season, will the product still be effective next Spring? I would store it in my basement over the Winter. Thanks.

    1. Copy-pasted from Summit Chemical: “Mosquito Dunks® can be stored indefinitely because, technically
      speaking, the dried B.t.i. in Mosquito Dunks® is not living, viable
      bacteria.” And: “As long as the product is stored under 100 degrees and out of direct sunlight the product will be effective for years. Over long periods of time, 3+ years, the product may lose some efficacy, but will still be safe.”

  6. Can you use these in an above ground pool that is active? Will it hurt or injure humans if exposed? If yes how long should someone wait to go swimming after use?

    1. I’m amazed at how many products contain this disclaimer and I sometimes wonder if it’s just some kind of lawyer catch all in case there’s some kind of allergic reaction. Although, I don’t truly know the answer to your question.

    1. Shouldn’t be a problem. Would probably help control any fungus gnats by killing any of their larvae in the soil. I crumble dunks into potted plant soil to help control larvae when they ingest it.

  7. I have BMC liquid. I’m not sure whether it is two years or three years old. Is it still effective or should I replace it?

  8. what can be used for houseplants that have a self-watering water well to keep plants
    watered for a longer time to keep the mosquitos from breeding and not harm the plants?

  9. The package states that it has 10.31% “insecticidal toxins” listed on the first two lines of ingredients. The back of the package then warns that this product is hazardous, do not place near potable water for humans, to wash thoroughly after you touch it and don’t ingest accidentally, blah blah blah. Can anyone attest to the safety of these “toxins”? I thought Dunks and Bits were just a biological ingredient, a dead spore, in an inert delivery system. Nowhere did any of the online, commendatory literature indicate that there were “toxins”. I discovered this after I made the purchase.

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