Common Garter Snake

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Common Garter Snake
Thamnophis sirtalis sirtalis Wooster.jpg
Thamnophis sirtalis sirtalis
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Colubridae
Subfamily: Natricinae
Genus: Thamnophis
Species: T. sirtalis
Binomial name
Thamnophis sirtalis
(Linnaeus, 1758)

13 sspp., see text

  • Coluber sirtalis Linnaeus, 1758
  • Tropidonotus sirtalis Holbrook, 1842
  • Tropidonotus ordinatus
    Holbrook, 1842
  • Eutainia sirtalis Baird & Girard, 1853
  • Eutænia sirtalis Cope, 1875
  • Thamnophis sirtalis Garman, 1892

The Common Garter Snake (Thamnophis sirtalis) is an indigenous North American snake found widely across the continent. Most garter snakes have a pattern of yellow stripes on a brown or green background and their average length is about 55 cm (22 in), with a maximum length of about 137 cm (54 in).[1][2] The average body mass is 150 g (5.3 oz).[3]


Current scientific classification recognizes thirteen subspecies (ordered by date):[4]


Garter snakes are very thin snakes. None grow over about 4 feet long and most stay smaller. Most have longitudinal stripes in many different colors. Garters come in a wide range of colors including: green, blue, yellow, gold, red, orange, brown, and black

Life history[edit]

The Common Garter Snake is a diurnal snake. In summer, it is most active in the morning and late afternoon; in cooler seasons or climates, it restricts its activity to the warm afternoons.

In warmer southern areas, the snake is active year-round; otherwise, it sleeps in common dens, sometimes in great numbers. On warm winter afternoons, some snakes have been observed emerging from their hibernacula to bask in the sun.


The saliva of a garter snake may be toxic to amphibians and other small animals. For humans, a bite is not dangerous, though it may cause slight itching, burning, and/or swelling. Most garter snakes also secrete a foul-smelling fluid from postanal glands when handled or harmed.

Garter Snakes are resistant to most naturally found poisons such as that of the American Toad and Rough-Skinned Newt, the latter of which can kill a human if ingested. Garter snakes have the ability to absorb the toxin from the newts into their body making them poisonous, which can deter potential predators.[5]


In the early part of spring, when snakes are coming out of hibernation the males generally emerge first to be ready when the females wake up. Some males will assume the role of a female and lead other males away from the burrow, luring them with a fake female pheromone. After such a male has led rivals away, he "turns" back into a male and races back to the den, just as the females emerge. He is then the first to mate with all the females he can catch. There are generally far more males than females and that is why, during mating season, they form "mating balls," where one or two females will be completely swamped by ten or more males. Sometimes a male snake will mate with a female before hibernation and the female will store the sperm internally until spring, when she will allow her eggs to be fertilized. If she mates again in the spring, the fall sperm will degenerate, and the spring sperm will fertilize her eggs. The females may give birth ovoviviparously to 12 to 40 young from July through October.


The habitat of the garter snake ranges from forests, fields, and prairies to streams, wetlands, meadows, marshes, and ponds, and it is often found near water. It is found at altitudes from sea level to mountain locations. Their diet consists mainly of amphibians and earthworms, but also fish, small birds, and rodents. Garter snakes are effective at catching fast-moving creatures like fish and tadpoles. Animals that eat the Common Garter Snake include large fish (such as bass and catfish), bullfrogs, snapping turtles, larger snakes, hawks, raccoons, foxes, wild turkeys and domestic cats and dogs.


Water contamination, urban expansion, and residential and industrial development are all threats to the garter snake. The San Francisco Garter Snake (T. s. tetrataenia), which is extremely scarce and occurs only in the vicinity of ponds and reservoirs in San Mateo County, California, has been listed as an endangered species by the U.S. Fish and Wildlife Service since 1967.

Anti-predatory displays[edit]

Garter snakes exhibit many different anti-predatory behaviors, or behaviors that ward off predators. Morphology refers to the shape that the snake’s body makes in response to the environment, predatory defense, mating, etc. The term body geometry may also be used to describe the shape a snake's body makes. Garter snakes exhibit a higher variation of morphology when compared to other snakes. Predation has been such an intense selection pressure throughout evolution; these snakes have developed body geometries that are highly variable and heritable.[6] These morphologies have been concluded to be highly variable even within a single population.[7] Different geometries indicate whether the snake is preparing to flee, fight, or protect itself. Since the traits are heritable, there must be some evolutionary benefit such as warding off predators. Additional research also shows that different biological factors such as body temperature and sex influence whether the snake will exhibit certain anti-predatory behaviors.[8]

Studies show that the warmer the temperature of a Garter snake, the more likely the snake is to flee a predator. While a snake with a cooler body temperature remains stationary or attacks. Male garter snakes are also more likely to flee.[9] Garter Snakes that exhibit more aggressive anti-predatory displays tend to also be fast and have high stamina. However the cause for correlation is unknown.[10]

Aposematism, or warning coloration, is another factor that influences anti-predator behavior. For example, the coral snake exhibits aposematic coloration that can be mimicked.[11] While garter snakes do not exhibit mimicry or aposematic coloration, it has been found that garter snakes with striped patterns are more likely to slowly, successively crawl away, while spotted and not striped snakes were more likely to deceptively flee from predators.[12]

The decision of a juvenile garter snake to attack a predator can be affected by whether the snake has just eaten or not.[13] Snakes that have just eaten are more likely to strike a predator or stimuli than snakes that do not have a full stomach. Snakes are more likely to flee a threatening situation if their stomachs are empty.[14] Snakes that have just eaten a large animal are less mobile. Feeding positively affects endurance as opposed to speed.[15]

Another factor that controls the anti-predatory response of the garter snake is where the snake attacked. Many birds and mammals prefer to attack the head of the snake.[16] In a research study, it was found that garter snakes are more likely to hide their head and move their tail back and forth when being attacked close to the head.[17] The same study concluded that snakes that were attacked in the middle of their body were more likely to flee or exhibit open-mouthed warning reactions.[18]

Time may be another factor that contributes to anti-predatory responses. Garter snakes are affected by maturation time.[19] As snakes mature, the length of time at which garter snakes can display physical activity at 25°C increases. Juvenile snakes can only be physically active for three to five minutes. Adult snakes can be physically active for up to 25 minutes.[20] This is mostly due to aerobic energy production; pulmonary aeration increases up to three times in adult garter snakes when compared to juveniles.[21] The quick fatigue of the juveniles most certainly limits the habitats they can live in as well as their food source.[22] It absolutely affects the anti-predator response of both juvenile and adult garter snakes; without sufficient energy production the snake cannot exhibit any anti-predatory response.

Female garter snakes produce a specific pheromone. Studies show that some males of various species of garter snake exhibit female behavior as well as morphology.[23] This type of mimicry is primarily found in the red-sided garter snake. A portion of the males that exhibit female mimicry also secrete the sex-specific hormone to attract other males.[24] In a study these “she-males” mated with females significantly more often than males that did not exhibit this mimicry.[25] A male pretending to be a female around other males increases his chances of reproduction as well as protects against stronger, more aggressive males.

See also[edit]


  1. ^ Conant, Roger. 1975. A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Houghton Mifflin. Boston.
  2. ^ [1]
  3. ^ [2]
  4. ^ Thamnophis sirtalis , Reptile Database
  5. ^ Williams BL, Brodie ED Jr,Brodie ED 3rd. (2004). A resistant predator and its toxic prey: Persistence of newt toxin leads to poisonous (not venomous) snakes. J Chem Ecol 30(10):1901-19.
  6. ^ Garland, 1988. pp. 335-350.
  7. ^ Garland, 1988. pp. 335-350.
  8. ^ Shine, 1999. pp. 239-245.
  9. ^ Shine, 1999. pp. 239-245.
  10. ^ Brodie, 1992. pp. 1284-1298.
  11. ^ Greene, 1981. pp. 1207-1212.
  12. ^ Arnold, 1984. pp. 1108-1118.
  13. ^ Herzog, 1987. pp. 387-389.
  14. ^ Herzog, 1987. pp. 387-389.
  15. ^ Herzog, 1987. pp. 387-389.
  16. ^ Langkilde, 2004. pp. 937-947.
  17. ^ Langkilde, 2004. pp. 937-947.
  18. ^ Langkilde, 2004. pp. 937-947.
  19. ^ Pough, 1977. pp. 337-345.
  20. ^ Pough, 1977. pp. 337-345.
  21. ^ Pough, 1977. pp. 337-345.
  22. ^ Pough, 1977. pp. 337-345.
  23. ^ Mason, 1985. pp. 59-60.
  24. ^ Mason, 1985. pp. 59-60.
  25. ^ Mason, 1985. pp. 59-60.
  • "Thamnophis sirtalis". Integrated Taxonomic Information System. Retrieved 6 February 2006. 
  • Care of Garter Snakes
  • Garter Snake Information
  • Caring for Your Garter Snake
  • "IUCN Red List of Threatened Species". Retrieved 2008-09-06. 
  • Shine, R., M.M. Olsson, M.P. Lesmaster, I.T. Moore and R.T. Mason. (1999). Effects of Sex, Body, Size, Temperature & Location on the Antipredator Tactics of Free-Ranging Gartner Snakes (Thamnophis sirtalis, Colubridae). Oxford Journal 11 (3), 239 -245
  • Garland, T. (1988). Genetic Basis of Activity Metabolism. I. Inheritance of Speed, Stamina & Antipredator Display in the Garter Snake, Thamnophis sirtalis. Evolution 42(2), 335-350
  • Brodie III, E.D. (1992). Correlational Selection For Color Pattern & Antipredator Behavior In The Garter Snake. Evolution 46(5), 1284-1298.
  • Greene, H.W. and R.W. McDiarmid. (1981). Coral Snake Mimicry: Does It Occur? Science 213, 1207-1212.
  • Arnold, S.J., & A.F Bennett. (1984). Behavioural Variation in Natural Population III: Antipredator Display in the Garter Snake Thamnophis Radix. Animal Behavior 32, 1108-1118.
  • Mason, Robert T., and David Crews. "Female Mimicry in Garter Snakes." Nature 316 (1985): 59-60.
  • Herzog, Harold A., Jr., and Bonnie D. Bailey. "Development of Antipredator Responses in Snakes: II. Effects." Journal of Comparative Psychology 101 (1987): 387-389. Web.
  • Herzog, H. A., Bowers, B. B., & Burghardt, G. M. (1989). Stimulus control of antipredator behavior in newborn and juvenile garter snakes (thamnophis). Journal of Comparative Psychology, 103(3), 233-242.
  • Langkilde, Tracy, Richard Shine, and Robert T. Mason. "Predatory Attacks to the Head vs. Body Modify Behavioral Responses of Garter Snakes." Ethology 110.12 (2004): 937-947.
  • Pough, F. Harvey. "Ontogenetic Change in Blood Oxygen Capacity and Maximum Activity in Garter Snakes (Thamnophis Sirtalis)." Journal of Comparative Physiology 116.3 (1977): 337-345.

External links[edit]