Pet owner Joe Kaiser knows firsthand how important it is to protect his two dogs. He's a volunteer with the local humane society. "I see too many animals with heartworm coming in with fleas and ticks and I see this and I feel so sorry for them because they are suffering." Angie Hicks with Angie's List adds, "Especially during these summer months preventative care for your pets is important when it comes to parasites because it's very easy for them to pick up fleas, for example. The treatment is much more expensive than the preventative maintenance is."Of those three common parasites, fleas are the most common. Dr. Greg Magnusson, a veterinarian, says, "They can make pets who are allergic to fleas very sick as far as their skin is concerned. Flea allergy dermatitis is one of our most common presenting signs in the spring and summer."