Do flea collars kill fleas already on dogs? Flea and tick collars work similarly to how topical flea and tick treatments work in that they both directly administer the active ingredients onto the dog’s fur. What Is A Flea And Tick Collar And How Does It Work Dog Flea Treatment Fleas Flea Control For Dogs But some flea collars perform only one of. How do flea collars work on dogs . However, the fleas that stay from away from the collar can continue to bite. The only things flea will usually do is bite and run. If you’ve suddenly had a flea infestation, it may take a long time for all of the fleas in the environment to hatch and eventually be killed by the collar alone. Many dogs wear the seresto flea collar without issue, but there have been. The repellent is released in gas form from the collar. The second type of flea collar kills fleas after the flea has bitten your dog. Hence, the active ingredients must be spread over the regions where the flea is supposed to ...