A hemorrhagic virus carried by biting gnats has taken hold among white-tailed deer in four Michigan counties, confronting hunters and wildlife managers with the particular grief of watching a population die not by harvest but by disease. EHD — epizootic hemorrhagic disease — poses no threat to humans, yet its arrival speaks to a broader pattern of ecological disruption that has grown more frequent and more geographically ambitious in recent years. As Michigan moves toward its fall hunting season, the state finds itself asking its most attentive outdoor citizens to become, in effect, sentinels