Bti kills mosquitoes, not everything else

Bti kills mosquito larvae by releasing a toxin that shuts down their gut — and it leaves fish, frogs, and beneficial insects alone.

This is the biological control everyone should be using in standing water. Bacillus thuringiensis israelensis is a naturally occurring soil bacterium that produces a protein crystal. When mosquito larvae eat it, that crystal dissolves in their alkaline gut and punches holes in their stomach lining. They stop feeding and die within a day or two.

The important part: the toxin only activates in the specific pH and enzyme conditions of mosquitoes, black flies, and a few close relatives. It doesn’t affect dragonfly nymphs, beetles, fish, amphibians, birds, or mammals. You can toss a Bti donut in a pond and forget about it for a month.

It’s not a cure-all. Bti kills larvae, not adult mosquitoes. You need to treat water before they emerge. And it degrades in sunlight and heat, so you have to reapply. But it’s about as targeted and safe as pest control gets.

Don’t overthink it. Buy a box of mosquito dunks, toss one in your pond, and move on.