Cigarette butts are some of the most commonly littered items around the world. If you do a litter cleanup in your neighborhood, save used cigarette butts to create a free and easy DIY nicotine insecticide for your plants. Nicotine is toxic to harmful insects like aphids, gnats and leafhoppers, but is relatively harmless to good insects like bees and ladybugs. To make a nicotine insecticide, simply soak 1-cup cigarette butts in 1-gallon warm water with 1/4-teaspoon soap flakes for 30 minutes. Strain and put the mixture in a spray bottle and spray away.