Illinois Natural History Survey - University of Illinois

Gartersnakes

 

Jen Mui

 

Ask any child what kind of snake they’ve seen and more often than not, the answer will be a “garden” or “gardener” snake.  Most likely, they are referring to one of the species of gartersnake. 
    

Across North America, there are 16 species of gartersnakes in the genus Thamnophis and four of those are found in Illinois.  The Common and Plains Gartersnakes, and the Eastern and Western Ribbonsnakes, are typically dark with light stripes running the length of their bodies. 
      The Common Gartersnake, Thamnophis sirtalis, is found across much of North America, from the Pacific Ocean to the Atlantic Ocean and from Florida to Southern Alaska — it is absent from the desert southwest.  They are fairly cold tolerant and found further north than any other snake in North America.  Because of their tolerance for cold temperatures, they have a longer active period than other snakes.  In Illinois, gartersnakes have been seen basking during warm winter days, and are the first snakes to emerge each year and among the last to hibernate in fall.
     Gartersnakes will often return to the same den year after year, possibly using landmarks or following scent trails.  Most gartersnakes overwinter in dens individually or in small groups, but thousands of individuals overwinter in a communal den in Manitoba each year.  In Illinois, gartersnakes have been found overwintering in crayfish burrows with other species, including the endangered Eastern Massasauga Rattlesnake.
     Soon after emerging from their dens, gartersnakes mate, often forming “mating balls” in which one female is surrounded by multiple males.  Gartersnakes do not lay eggs, instead giving birth to up to 40 neonates in summer or early fall.  Gravid female gartersnakes will often gather together in summer just before giving birth.  Parental care ends at birth, with the neonates being on their own to find food and shelter before winter.
     Gartersnake prey include fish, invertebrates, amphibians, and occasionally small mammals. Snakes are able to unhinge their bottom jaws and open wide enough to swallow prey that are larger than their own heads.  As a group, gartersnakes are seen as active foragers, moving through their habitat searching for prey.  Gartersnakes “taste” the air, rapidly flicking their forked tongues, collecting chemicals that are identified in the vomeronasal system in the roof of the mouth.  The chemicals help identify potential mates, prey, or predators.  Gartersnakes also have very good vision, particularly underwater.
     Gartersnakes are technically venomous, producing a compound that breaks down proteins and causes hemorrhaging (excessive bleeding) in prey.  Gartersnakes do not pose a serious threat to humans because, unlike vipers, gartersnakes do not have long hollow fangs or the ability to store large amounts of venom.  Some people who have been bitten by gartersnakes have reported itchiness or slight swelling.
     The Common Gartersnake is found across Illinois in a variety of habitats — forests, edge habitats, and urban areas, often near water.  The closely related Plains Gartersnake, Thamnophis radix, is found in more open areas — old prairies, pastures, vacant lots, and marshes. 
     Despite their lack of arms and legs, gartersnakes are very mobile, both on land and in water.  Their skeletons are made up of hundreds of vertebrae locked together, each with a pair of ribs that can move forwards, backwards, and up and down, allowing the snake to bend and move with ease.  They often make long migrations between their overwintering dens and summer foraging habitats or between foraging habitats. As the habitats become more fragmented, snakes must cross more barriers including roads, where they are more vulnerable to predators and vehicles.
     Predators include hawks, jays, crows, mammals, larger snakes, large frogs, and large fish.  When threatened, gartersnakes may flee, strike, or void their cloacal scent glands and defecate.  The musk produced repels would-be predators, and is difficult to get rid of if it gets on you.
     As always, wild animals should be observed and respected, but not handled, for your safety and theirs.
     Learn more about Illinois habitats and species at
http://wwx.inhs.illinois.edu/animals-plants/

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