Bti is a sniper, not a bomb.

Bacterial larvicides like Bti work by producing a protein crystal that only poisons the gut of mosquito larvae when they eat it.

Bti stands for Bacillus thuringiensis israelensis, a naturally occurring soil bacterium. When you throw those little donuts or granules into standing water, the bacteria release a toxin that attacks the alkaline gut of mosquito and black fly larvae. The key is selectivity. The toxin binds to specific receptors in those insects’ guts that mammals, birds, fish, and even other bugs don’t have. So you’re not nuking the pond – you’re just hitting the mosquitoes.

The larvae stop feeding within minutes and die a day later. The bacteria itself degrades in sunlight and water pretty fast, usually within a couple of days, which means you have to reapply if you want sustained control. It’s not a one-and-done solution.

That specificity is why Bti is the go-to for mosquito control without collateral damage. No honeybees dying, no fish kills, no weird resistance issues if you rotate other methods now and then.

Only downside: you have to hit the water at the right time, when larvae are actively feeding. But for standing water you can’t drain, it’s the best tool.