When Rick Ostfeld gets bitten by a tick, he knows right away. After decades studying tick-borne diseases as an ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, Ostfeld has been bitten more than 100 times, and his body now reacts to tick saliva with an intense burning sensation. He’s an exception. Most people don’t even notice that they’ve been bitten until after the pest has had time to suck up a blood meal and transfer any infections it has circulating in its spit.