The eastern milk snake (Lampropeltis triangulum) is the only member in Chicago Wilderness of the group of constrictors called "king snakes." Constrictors kill their prey by asphyxiation. King snakes get their name because they often kill and eat other species of snakes, including venomous species such as rattlesnakes.

In Chicago Wilderness, the eastern milk snake may make a meal of DeKay's brown snakes (Storeria dekayi), red-bellied snakes (Storeria occipitomaculata), or eastern garter snakes (Thamnophis sirtalis). The eastern milk snake is the most widespread and variable species of king snake, ranging from southeast Canada, west to the Rocky Mountains, and south to northern and western parts of South America.

The eastern milk snake is a medium-sized species and grows to a length of about three feet. It has smooth, often shiny scales. In the Chicago region, individuals normally are tan in color, with reddish-brown blotches bordered by black. The belly is usually whitish with black spots, which form a rough checkerboard pattern.

Milk snakes mate in the spring. In summer, they lay up to about 20 eggs in decomposing vegetation, hollow logs, or similar humid, warm spots. The eggs hatch in about 60 days, and the hatchlings are usually around ten inches in length.

Appropriately, there is a dietary story behind the common name of our local king snake. Besides its occasional taste for reptilian prey — as well as frogs, fish, birds, and eggs — the milk snake avidly hunts small mammals such as mice and voles. After European settlement of North America, the milk snake's searches for these rodents soon brought it into close quarters with humans. Milk snakes were undoubtedly drawn to mice that foraged on waste grain, and there they found shelter in barns and other farm buildings. Humans who encountered milk snakes in their barns creatively imagined that these creatures came to milk the cows, hence the name "milk" snake. In the Chicago Wilderness region, milk snakes are still found in and around some remaining farm sites.

A look at the milk snake's local distribution and habitat suggests that while early farmers may have viewed it as a rogue cow milker intruding on their barns, the snake was actually hosting the farmers on its home turf. While Lampropeltis triangulum is not rare in our urbanizing region, most local herpetologists note a correlation between its scattered populations and remnant oak savanna groves, especially those on gravelly, morainal ridges. These open woodlots are transitional ecosystems lying between the open grasslands and the more closed-canopy forest. Milk snakes are rarely found on wet soils and seem to prefer the gravelly or rocky soil of these low but dry hills. They probably also use the mix of shade and sun found in savannas to regulate body temperature.

As our region was settled in the 19th century, farmers preferred to build their farmsteads on these same savannas, especially those on the drier ridges, while they converted the surrounding and often wet prairies into row crops or used them to graze cattle for the once-important dairy farms. The resident milk snakes simply capitalized on the nearby mix of cover and food that the new settlements provided. While many farmers probably loathed the presence of these reptiles, the snakes provided them an important service by regulating mouse populations on the farms.

Milk snakes are secretive and fairly difficult to find together in any number, even where sizable populations are known to occur. Many local conservation agencies have acquired savannas, often in the form of vacated farm sites, where milk snakes persist. In these preserves, visitors may encounter milk snakes under wood, tin, cattle tanks, or other debris left over from the farms. Milk snakes are non-venomous. While individuals may bite in defense when captured, they are harmless to humans.

The milk snake's close relationship with Chicago farms has greatly diminished over the last century. But as restoration efforts continue, these interesting animals should rightfully reclaim their original role as indicators of the savanna heritage of Chicago Wilderness.

— Michael Redmer