Come summertime, some of us here at Shots are reminded, as we lounge on decks and venture into overgrown gardens, that we are irresistible to mosquitoes. As we gripe about our itchy, pocked limbs, we can't help but wonder just why they unfailingly devour us and pass over our friends and loved ones. And when it comes to repellent, it's hard to tell just what works best.

So we called up Dr. Roger Nasci, chief of the branch of the Centers for Disease Control and Prevention that tracks insect-borne viruses, to get some answers to our summertime mosquito quandaries.

Q: So why is it that backyard mosquitoes swarm and feast on some people, while others seem to be less palatable to them? Is there any truth to the claim that some blood is sweeter?

A: Well, first off, let's remember that here in the U.S. we have 175 species of mosquitoes, and a relatively small number of them feed on people. But they'll feed on anything that has blood.