 Harmful to mosquito larvae, harmless to everything else. So birds can drink it, dogs can drink it, horse can drink it, any kind of container holding water. We sell an awful lot to ranchers and farmers. They have stock tanks. They need for their livestock to drink, but that's a prime area for mosquitoes. So they throw a dunk or a piece of dunk in that every 30 days or so, and that keeps the mosquitoes from breeding there.