Seresto collars contain two active ingredients: Imidacloprid and Flumethrin. Imidacloprid is an insecticide that works by interfering with the nervous system of the fleas and ticks, ultimately killing them. It is a synthetic version of a naturally-occurring chemical found in plants such as tobacco and garlic. Flumethrin is a pyrethroid insecticide that works by disrupting… Continue reading What ingredients are in Seresto collars