Eastern Massasauga Rattlesnake, Sistrurus catenatus catenatus, ranges from central New York and southern Ontario to central Illinois and eastern Iowa. Historically, the snake’s range covered this same area, but within this large area the number of populations and numbers of snakes within populations have steadily shrunk. Generally, only small, isolated populations remain. The eastern massasauga is listed as endangered, threatened, or a species of concern in every state and province where it is found. It is unlikely a dog will encounter this snake unless it is roaming in wetland areas. Other subspecies of Sistrurus catenatus occur to the west. Its venom has caused human deaths.
The Dusky Pigmy Rattlesnake inhabits most of Florida, excluding the Florida Keys. Outside of Florida, it occurs north to North Carolina and west to eastern Texas and southern Missouri.It uses lowland pine flatwoods, prairies, and the edges of freshwater marshes and cypress swamps. It is a small rattlesnake with venom that is rarely fatal (but fatalities have been reported).