these medicines aren't preventative, they're also used to cure existing infections. although they gave him all the serious shots, my dog still came home from the shelter with tapeworm and fleas. the grain-free organic-chicken based dog food i feed him isn't going to help with that. neither is letting him out into a field to kill some furry things (and believe me he loves to do that, he's a terrier).

also, dogs don't usually get worms and fleas from killing small animals, they get them from other dogs. just like people, if you live in the city (with dog daycare, dog parks, lots of other dogs playing on walks) it's a bigger problem than if you live in the suburbs or countryside and you have a mini-pack of your own dogs on your home property.

also, nobody ever said fleas or worms will kill your dog, it just makes life absolutely miserable for both the dog and the owner.