Comfortis is the best. It's the only thing that gives our dogs relief once those darn fleas move in for the summer!Comfortis is also great for fleas. It's a pill for the dogs that you get from the vet. Kills all of the fleas on them in 24 hours, then protects for 30 days. DE would also work well for fleas. Might be cheaper than nematodes. I do want to try nematodes one of these days. They're also supposed to work great on ants.