Biting insects can be bothersome during warm weather. Parasitic deer ticks (which are known to carry Lyme disease) are a hazard. The trail passes through black bear habitat (especially the northern portions), although problems with bears are rare. More likely are problematic encounters with feral and domestic dogs. Skunks, raccoons, and porcupines are common and active after dark. Venomous snakes are considered extinct along most of the route, with the possible exception of the warm, dry microclimates on the Metacomet Ridge. Poison ivy is native to the M&M Trail ecosystems, but it occurs with less frequency north of the Holyoke Range, and does not thrive on Mount Monadnock at all.