STEM Kills Flies, Mosquitoes and Gnats is a bug spray for home and outdoor use made with botanical extracts that are deadly for bugs. STEM plant-based active ingredient bug spray is formulated with botanical extracts to kill flies, mosquitoes and gnats. Our insect killer was tested by entomologists and is safe for use around pets and people when used as directed. It has no added dye, fragrance, or harsh chemical odors and is made for indoor and outdoor use.