Three days after a 9-year-old Connecticut boy started to hear a strange buzzing sound in his ear, his parents took him to a doctor at Yale New Haven Children’s Hospital. The boy reported that he had no pain in his ear, no hearing loss, and no ringing or signs of tinnitus. He said he’d been playing outdoors recently on school days. Then the doctor, Erik Waldman, looked into the boy’s ear and saw a true vision of horror—a brown arachnid burrowing into the epidermal layer of the eardrum and feasting on the child’s blood. The tick couldn’t be removed at...