Seresto, 27.5" Adjustable, Large Dog Flea & Tick Collar, For 8 Month Protection Against Fleas & Ticks For Puppies 7 Weeks Of Age & Older & Dogs Weighing Over 18 LB, Starts To Repel & Kill Fleas Within 24 Hours Of Initial Application & Re-Infesting Fleas Within 2 Hours, Repels & Kills Ticks Within 48 Hours Of Initial Application & Re-Infesting Ticks Within In 6 Hours, Works On Contact, Odorless & Non-Greasy, Quick Release Feature & Visibility Reflectors Provide Extra Safety, Water Resistant Formula Continues Working For Up To Eight Months, Even After Bathing, Swimming & Sun Exposure.