Hydrogen peroxide will kill many kinds of insects, including fleas. I fill a spray bottle with water and add several tablespoons of hydrogen peroxide with another teaspoon or so of dish detergent. Flies and other insects will die within seconds if you spray them. I use this every summer when flies get in my house. I use it on the windows and windowsills only and clean up right away. Works in the yard, too, in a hose-end sprayer, with proportions greatly increased for the size of the yard. Doesn't hurt the grass or most plants, but be careful around roses. Keep the mixture away from the leaves of roses or wash thoroughly afterward. Hydrogen peroxide alone can be used on outside plants and the yard, as it is essentially non-toxic.
