 So these mosquito dunks should last about 30 days in our rain barrel here, and they will help prevent mosquito larvae from hatching. From what I've read and seen on the internet, including various bird and plant websites, these are not harmful to humans, pets, plants, bees, birds. They are safe to use in bird baths, ponds, and anywhere where there might be some stagnant water sitting that mosquito larvae will set up in. According to the directions, it takes about 48 hours for this to kick in and as I said, it should be good for about 30 days before you need to change it out. Another thing I like to use the mosquito dunks for is our compost pail. We have this just sitting outside our door into the garage that we dump our coffee grinds and all our compost vegetables and stuff, and it gets very infested with fruit flies. So what I've started doing here, as you can see when I open it, no fruit flies coming out. There usually is hundreds flying out of here. So every time I have to go dump my pail into my compost pile, I have a jar here of some of these mosquito dunks that's half dissolved in this jar. Just pour a little splash in every once in a while. And it really seems to keep the fruit flies at bay.