In western Manitoba, creek and river valley marshes provide summer habitat with major den sites in eroding shale outcrops. Snakes reach the northernmost extent of their range near Flin Flon. P opulation densities are greatest in the Interlake where a proliferation of marshes, shallow lakes and poor drainage offer ideal summer habitat and breaks in the limestone bedrock provide denning sites. Some dens are on islands where rock outcrops or pressure ridges provide access to suitable wintering habitat. Snakes grow throughout life, their length being related to food availability and lifespan.
Females are typically larger than males of all year classes.
Undisturbed snake dens contain many sizes of snakes, indicating that a number of year classes are present. Dens that have been disturbed or where harvest has occurred typically contain high percentages of small animals. Nearly all snakes more than 90cm long are females over 10 years old while males reach a maximum length of 75cm. The chances of a snake reaching 12 years of age are less than 1 in 5,000. A parasitic fluke often causes wild snakes to lose the ends of their tails and may be responsible for breeding failures.