Whether they like them or fear them, people find snakes fascinating. Despite being legless, snakes inhabit most environments on Earth that are ice free for at least part of the year. Deserts, oceans, forests, grasslands, lakes, rivers, marshes, mountains, farms, and cities - all are homes to some of the 2400 known species of snakes. Only 17 species are found in Michigan, but they are an important and conspicuous part of our state's fauna.
Adaptation and History
Snakes, along with the lizards, turtles, crocodiles, and alligators, are reptiles. This means that they are lung breathing, back boned animals covered by dry horny scales. Their young, hatched from shelled eggs or born alive, are essentially miniature versions of their parents. Reptiles depend on the outside environment for body heat, unlike birds and mammals which can produce heat internally. Snakes differ from other reptiles in being legless and in lacking both eyelids and external ear openings. Their eyes are covered by a protective transparent scale, and they hear by picking up vibrations through their skull and jaw bones. The constantly flicking forked tongue is used to augment the sense of smell. Odor particles are picked up and deposited on a special organ in the roof of the snake's mouth which then sends information to the brain. This sense of smell assists the snake in finding food and identifying potential mates or enemies. The tongue of a snake is never a "stinger" or weapon.
Snakes evolved from lizard ancestors about 100 million years ago, late in the Mesozoic Era (the "age of dinosaurs"). Some lizard groups today are still in the process of becoming legless, and certain primitive snakes, like boas, still have remnants of hind limb and hip bones in their bodies. Leglessness may be beneficial in some environments, as when burrowing underground or moving through thick vegetation. Snakes move with great agility, using from 200 to 400 pairs of ribs connected in turn to muscles and the large belly scales. The specialized backbones (vertebrae) allow free lateral movement, but restrict vertical movement, and some tree climbing species can "lock" their vertebrae to assist in bridging between branches. The internal organs are arranged to accommodate the elongated body shape, and most snakes have only one fully-developed lung, the other being small and degenerate.
All snakes are predators. The smaller Michigan snakes feed on invertebrates such as worms, slugs, or insects. The larger species take larger prey, such as frogs, rodents, birds, or other reptiles. (Preferred foods for each species are noted in the individual accounts above.) Snakes must swallow their food whole. This is possible due to flexible connections between many of their skull and jaw bones and stretchable skin, allowing them to swallow prey items larger than their heads.
Non venomous snakes have tiny, recurved teeth that are useful for holding and swallowing prey. Venomous species have these recurved teeth, as well as enlarged teeth for injecting poison. A rattlesnake's fangs are hollow and function like hypodermic needles to conduct venom from special glands into the body of its prey. Rattlesnake venom is a specialized form of saliva that not only kills small food animals but also begins the digestive process. The amount of venom injected in a bite varies, depending on the angle and force of the strike and the supply of venom available. About 30% of rattler bites are "dry", which may account for the reported successes of folk remedies and miracle "cures." Any bite from Michigan's one poisonous species, the Eastern massasauga, should get prompt medical attention.
Conversely, a bite from a non venomous snake can normally be treated as one would a scratch or puncture wound, with ample precaution against infection. (Simply leaving snakes alone and using care when walking in natural areas will prevent nearly all bites - these creatures do not seek confrontation with humans and accidental bites are rare.)
Like nearly all reptiles, snakes adjust their body temperature by moving in and out of warm or cool places. In Michigan, most snakes probably prefer a body temperature of about 75 to 85 degrees F. Extended exposure to freezing conditions would be fatal, and they pass the winter in a dormant state in underground rodent burrows or other natural frost free shelters. Accessible basements and houses with cracked foundations may also attract shelter seeking snakes, often to the dismay of homeowners! The dry, scaly skin covering of snakes has no insulating properties, but does protect them as they move over rough or prickly terrain. The outer skin covering is shed and replaced several times during the year, and shed skins are good clues to the presence of secretive snakes.
Snakes usually mate in early spring, with males finding females by following their scent trails. Sometimes several males may court one female, and males of some species may fight "push and shove" battles over a female. Fertilization is internal. Although the majority of reptiles reproduce by laying shelled eggs, many snakes give birth to babies that develop inside the mother's body. Of Michigan's 17 snake species, 10 are live-bearing and 7 lay eggs. (Breeding habits for each snake are noted in the species descriptions, above.)
Egg-laying usually occurs in early summer, with the eggs deposited in an empty rodent burrow, in moist sand or soil, or under a log or stump. Most snakes abandon their nests soon after the eggs are laid, but females sometimes coil about the eggs for varying time periods. Hatching occurs in late summer or fall, the baby snakes cutting their way through the leathery egg shell using a special "egg tooth". Live-bearing snakes give birth about the same time in late summer. The babies often emerge enclosed in a thin membrane which soon ruptures. There is no parental care of the young, though they may remain near the female for several hours.
Snakes are undoubtedly the most misunderstood and feared of all animals in the state. This prejudice begins in our early childhood as we watch television programs and read stories that portray the snake as an evil and dangerous adversary, to be routinely avoided or destroyed. These fears are reinforced by watching a parent or friend react to a snake by either running from it or killing it. Fortunately the negative attitudes are beginning to change as people are exposed to environmental science programs at schools, nature centers, museums, and camps, and favorable publicity in the media.
More people now accept snakes for what they are - fascinating members of Michigan's wildlife community that, if given the chance, will avoid contact with humans. The vast majority are harmless, and the venomous species can be identified with minimal training and avoided with simple precautions when visiting natural areas. Some species that consume rodent or insect pests are beneficial to agriculture. All snakes play a role in the natural environment by contributing to ecological systems as predators and prey. They can best be conserved for the future by providing for their habitat needs and then simply leaving them alone.
The State of Michigan has enacted legislation to provide for the protection and regulation of native reptiles and Michigan recently amphibians. Rare and declining species are now protected from persecution and exploitation, and all species are affected by limits on numbers that can be taken or removed from the wild. Shooting of snakes and other reptiles is prohibited. Anyone wishing to take or study reptiles or amphibians (frogs, toads, salamanders) in Michigan should contact the Department of Natural Resources Fisheries Division for details and licensing requirements.