PYthon II MAGNUM is a sustained-release, plastic ear tag containing a synergized formulation of zetacypermethrin, a potent, enriched S-isomer pyrethroid compound. This insecticide has excellent activity against many pests, including horn flies that are resistant to certain other insecticides. PYthon II MAGNUM’s larger net weight of 0.54 oz. (15.4 grams) per tag provides greater insecticide release for maximum effectiveness against horn flies and other ectoparasites.