Move over mosquitos. There's another blood-sucking biter Americans need to guard against because it can spread disease: the sand fly.Sand flies are tiny tan flies — about a quarter of the size of a mosquito — that live in warm, wet, rural and forested areas. In other parts of the world, they are known to transmit a parasite — a single-celled organism — that causes an infectious disease called leishmaniasis. They're most active at night, and they're so tiny they can slip through ordinary mosquito nets on tents or window screens. "Sometimes you don't even notice that you've been bitten,"...