Mosquito Bits are small granules containing a naturally occurring bacterium that kills mosquito larvae and fungus gnat larvae within 24 hours of exposure. You sprinkle them directly into standing water outdoors or steep them into a “tea” for watering houseplants. The method depends on what you’re treating, and getting the ratio and timing right makes the difference between a quick fix and a persistent problem.
How Mosquito Bits Actually Work
The active ingredient is a soil bacterium called BTI (Bacillus thuringiensis israelensis). When larvae eat the granules or drink water containing BTI, the toxin destroys their gut lining. It’s highly specific: the toxin only activates in the alkaline digestive systems of mosquito and fungus gnat larvae, which is why it doesn’t harm most other organisms.
BTI has been registered with the EPA since 1961 and is exempt from the pesticide tolerance requirements that apply to most other products because of its low toxicity. It’s practically nontoxic to birds, fish, mammals, and bees. Studies on trout, bluegill sunfish, and other species found no harmful effects. Pets can drink treated water without risk, and you can safely use it in rain barrels, birdbaths, and fish ponds.
Using Mosquito Bits in Standing Water Outdoors
For small areas of standing water like birdbaths, plant saucers, tree holes, and rain gutters, sprinkle 1 teaspoon of Mosquito Bits per 25 square feet of water surface. If the water is relatively clean and you’re treating a larger area, use 4 ounces per 1,000 square feet. For water that’s murky, deep, or has a lot of organic debris, double that to 8 ounces per 1,000 square feet.
Just scatter the granules evenly across the water surface. They float initially, releasing BTI into the water as they absorb moisture. Larvae begin dying within 24 hours. You don’t need to remove the spent granules afterward.
When to Reapply
Reapplication depends on conditions. In heavily infested or dirty water, reapply every 7 days. In cleaner water with fewer larvae, every 14 days is sufficient. BTI breaks down in sunlight and doesn’t persist in the environment, so consistent retreatment is what keeps new generations of larvae from taking hold.
Making “Mosquito Bit Tea” for Houseplants
Fungus gnats, those tiny flies hovering around your potted plants, lay their eggs in moist soil. Their larvae feed on root hairs and organic matter in potting mix, and Mosquito Bits kill them the same way they kill mosquito larvae. The trick is getting the BTI into the soil where the larvae live, which means steeping the bits into water first.
Add 4 tablespoons of Mosquito Bits to a gallon of warm water. Placing the bits in a disposable paper tea bag or cheesecloth makes cleanup easier, but it’s not required. Let them soak for 30 minutes to 1 hour. Remove the bits (or tea bag), then use the water to water your plants as you normally would. The BTI-infused water soaks into the soil and kills larvae on contact.
Timing matters here. A single treatment won’t solve the problem because fungus gnats reproduce fast. At 75°F, a fungus gnat goes from egg to adult in about 17 days. Eggs hatch in 3 days, larvae develop over 10 days, and adults emerge after another 4 days as pupae. BTI doesn’t reproduce or persist in potting soil, so you need repeated applications. Use the Mosquito Bit tea for 2 to 3 consecutive waterings, or every 5 days if the infestation is heavy. This ensures you’re catching each new wave of larvae before they mature into flying adults.
Common Spots People Miss
Mosquitoes only need a bottle cap’s worth of water to breed. Walk around your yard and check every place water collects and sits for more than a few days: clogged gutters, old tires, the saucers under outdoor pots, wheelbarrows, tarps with pooled rainwater, and even the corrugated downspout extensions that hold water in their ridges. Treat anything you can’t dump out.
For fungus gnats indoors, the biggest missed opportunity is inconsistency. People treat once, see fewer gnats, and stop. But any eggs already in the soil will hatch days later and restart the cycle. Commit to at least three rounds of Mosquito Bit tea before calling it done. Letting the top inch of soil dry out between waterings also helps, since fungus gnat eggs and young larvae need constant moisture to survive.
Storage and Shelf Life
Mosquito Bits last up to 3 years when stored in a cool, dry place away from direct sunlight. Heat and moisture degrade the BTI over time, so keeping them in a sealed container in a garage or closet is ideal. Don’t store them near food or animal feed. If your bag has been sitting in a hot shed for a couple of summers, the bits may still work but will be less potent, meaning you’d need to apply a heavier rate or replace them.
Mosquito Bits vs. Mosquito Dunks
Both products use the same active ingredient, BTI, but they’re designed for different release speeds. Mosquito Bits are small corn cob granules that release BTI quickly, killing larvae within 24 hours. They’re best for a fast knockdown when you already see larvae wriggling in the water. Mosquito Dunks are larger donut-shaped discs that dissolve slowly over about 30 days, providing sustained prevention.
Many people use both: Bits first for the immediate kill, then a Dunk for ongoing protection in permanent water features like ponds, rain barrels, or drainage ditches. For houseplant fungus gnats, the Bits are the better choice because you need the BTI released quickly into soil, not slowly over weeks.