Hartz? UltraGuard Plus? Flea & Tick Collar for Dogs kills and repels both fleas and ticks for 7 months plus it kills and prevents flea eggs for up to 7 months thereby stopping the flea life cycle and preventing re-infestation. Water resistant. For use on puppies 6 weeks of age and older. READ ENTIRE LABEL BEFORE EACH USE. USE ONLY ON DOGS.