With about 35 recognized species and subspecies, garter snakes are highly variable in appearance; generally, they have large round eyes with rounded pupils, a slender build, keeled scales (appearing ‘raised’), and a pattern of longitudinal stripes that may or may not include spots (although some have no stripes at all). Certain subspecies have stripes of blue, yellow, or red, mixed with black tops and beige-tan underbelly markings. They also vary significantly in total length, from 18 to 51 in (46 to 130 cm).
With no real consensus on the classification of the species of Thamnophis, disagreements between taxonomists and disputed sources (such as field guides) are common. One area of debate, for example, is whether or not two specific types of snake are separate species, or subspecies of the same. Garter snakes are closely related to the genus Nerodia (water snakes), with some species having been moved back and forth between genera.
Garter snakes have been found to be one of the few species of snakes in the world to be both venomous and poisonous. However both are so medically insignificant that it would be extremely unlikely to harm even a human baby. The poisonous aspect comes from their diet so if they are not eating poisonous frogs they are not in fact poisonous as an individual.
Taxonomy
The first garter snake to be scientifically described was the eastern garter snake (now Thamnophis sirtalis sirtalis), by zoologist and taxonomist Carl Linnaeus in 1758. The genus Thamnophis was described by Leopold Fitzinger in 1843 as the genus for the garter snakes and ribbon snakes.[2] Many snakes previously identified as their own genera or species have been reclassified as species or subspecies in Thamnophis. The Reptile Database currently recognised 37 species in the genus, some with several subspecies.[3]
Garter snakes are not originally native to the eastern Canadian island of Newfoundland, but have been breeding there in the wild and gradually spreading since at least 2010. It is unknown how they reached the island, probably accidentally via hay shipments or as escaped pets.[4][5]
Their wide distribution is due to their varied diets and adaptability to different habitats, with varying proximity to water. However, in the western part of North America these snakes are more aquatic than in the eastern portion. Garter snakes live in a variety of habitats, including forests, woodlands, fields, grasslands and lawns, but never far from water, often an adjacent wetland, stream or pond. This reflects the fact that amphibians are a large part of their diet. Garter snakes are often found near small ponds with tall weeds.
Behavior
The posterior tooth of a garter snake
Garter snakes have complex pheromonal communication systems. They can find other snakes by following their pheromone-scented trails. Male and female skin pheromones are so different as to be immediately distinguishable. However, male garter snakes sometimes produce both male and female pheromones. During the mating season, this ability fools other males into attempting to mate with them. This causes the transfer of heat to them in kleptothermy, which is an advantage immediately after hibernation, allowing them to become more active.[6] Male snakes giving off both male and female pheromones have been shown to garner more copulations than normal males in the mating balls that form at the den when females enter the mating melee. A snake hatch can include as many as 57 young.[7]
Garter snakes use the vomeronasal organ to communicate via pheromones through tongue flicking, which gathers chemical cues in the environment. Upon entering the lumen of the organ, the chemical molecules will come into contact with the sensory cells, which are attached to the neurosensory epithelium of the vomeronasal organ.[citation needed]
If disturbed, a garter snake may coil and strike, but it typically hides its head and flails its tail. These snakes will also discharge a malodorous, musky-scented secretion from a gland near the cloaca. This secretion from North American garter snakes contains seven highly odoriferous volatile components: acetic, propanoic, 2-methylpropanoic, butanoic, and 3-methylbutanoic acids; and trimethylamine, and 2-piperidone.[8] They often use these techniques to escape when ensnared by a predator. They will also slither into the water to escape a predator on land. Hawks, crows, egrets, herons, cranes, raccoons, otters and other snake species (such as coral snakes and kingsnakes) will eat garter snakes, with even shrews and frogs eating the juveniles.
Close up of the scales on the back of the common garter snake
Being heterothermic, like all reptiles, garter snakes bask in the sun to regulate their body temperature. During brumation (the reptile equivalent of hibernation), garter snakes typically occupy large communal sites called hibernacula. These snakes will migrate large distances to brumate.
Social behavior
A long-term study by the Ontario Ministry of Transportation has shed light on the social behavior of Butler's garter snakes. The study, conducted in a 250-hectare area near Windsor, Canada, tracked over 3,000 individual snakes over a 12-year period. The findings challenge previous assumptions about solitary snake behavior and suggest that these snakes form social groups and communities. The study revealed that Butler's garter snakes do not wander randomly but instead tend to associate with specific groups of snakes. These groups typically consist of three to four individuals, with some larger groups reaching up to 46 snakes.[9][10]
Diet
Eating a frog
Garter snakes, like all snakes, are carnivorous. Their diet consists of almost any creature they are capable of overpowering: slugs, earthworms (nightcrawlers, as redworms are toxic to garter snakes), leeches, lizards, amphibians (including frog eggs), minnows, and rodents. When living near water, they eat other aquatic animals. The ribbon snake (Thamnophis saurita) in particular favors frogs (including tadpoles), readily eating them despite their strong chemical defenses. Food is swallowed whole. Garter snakes often adapt to eating whatever they can find and whenever they can find it because food can be either scarce or abundant. Although they feed mostly on live animals they will sometimes eat eggs.[11]
Venom
Garter snakes were long thought to be non-venomous, but discoveries in the early 2000s revealed that they produce a neurotoxic venom.[12] Despite this, garter snakes cannot seriously injure or kill humans with the small amounts of comparatively mild venom they produce and they also lack an effective means of delivering it. In a few cases, some swelling and bruising has been reported.[13] They do have enlarged teeth in the back of their mouth[14] but their gums are significantly larger and the secretions of their Duvernoy's gland are only mildly toxic.[13][15]
Evidence suggests that garter snake and newt populations share an evolutionary link in their tetrodotoxin resistance levels, implying co-evolution between predator and prey.[16] Garter snakes feeding on toxic newts can also retain those toxins in their liver for weeks, making those snakes poisonous as well as venomous.[17]
Conservation status
A mating ballA young garter snake
Despite the decline in their population from collection as pets (especially in the more northerly regions, in which large groups are collected at hibernation),[18] pollution of aquatic areas, and the introduction of American bullfrogs as potential predators, garter snakes are still some of the most commonly found reptiles in much of their ranges. The San Francisco garter snake (Thamnophis sirtalis tetrataenia), however, has been on the endangered list since 1969. Predation by crayfish has also been responsible for the decline of the narrow-headed garter snake (Thamnophis rufipunctatus).[19] Many breeders have bred all species of garter snakes, making it a popular breed.
northwestern Ohio, northeastern Indiana, the eastern portion of the Lower Peninsula of Michigan, and the adjacent extreme southern tip of Ontario, Canada.
In the above list, a binomial authority or a trinomial authority in parentheses indicates that the species or subspecies was originally described in a genus other than Thamnophis.
List of snakes, overview of all snake families and genera
References
^Wright AH, Wright AA (1957). Handbook of Snakes of the United States and Canada. Ithaca and London: Comstock Publishing Associates, a division of Cornell University Press. 1,105 pp. (in 2 volumes). (Thamnophis, p. 755).
^Wood, William F.; Parker, Joshua M.; Weldon, Paul J. (1995). "Volatile Components in Scent Gland Secretions of Garter Snakes (Thamnophis sp.)". J. Chemical Ecology. 21 (2): 213–219. doi:10.1007/BF02036652. PMID24234020.
^ abSmith, Michael (September 2001). "Duverney's Glands and "Warm" Herping". Cross Timbers Herpetologist. Dallas-Fort Worth Herpetological Society – via Melissa Kaplan's Herp Care Collection.
^Wright, Debra L.; Kardong, Kenneth V.; Bentley, David L. (1979). "The Functional Anatomy of the Teeth of the Western Terrestrial Garter Snake, Thamnophis elegans". Herpetologica. 35 (3): 223–228. JSTOR3891690.
^de Queiroz, Alan (September 27, 2010). "Garter Snakes". Online Nevada Encyclopedia. Nevada Humanities. Archived from the original on February 18, 2017. Retrieved December 29, 2016.
^Williams, Becky L.; Brodie, Edmund D. Jr.; Brodie, Edmund D. III (2003). "Coevolution of Deadly Toxins and Predator Resistance: Self-Assessment of Resistance by Garter Snakes Leads to Behavioral Rejection of Toxic Newt Prey". Herpetologica. 59 (2): 155–163. doi:10.1655/0018-0831(2003)059[0155:codtap]2.0.co;2. S2CID18028592.
^Williams, Becky L.; Brodie, Edmund D. Jr.; Brodie, Edmund D. III (2004). "A resistant predator and its toxic prey: persistence of newt toxin leads to poisonous (not venomous) snakes". Journal of Chemical Ecology. 30 (10): 1901–1919. doi:10.1023/B:JOEC.0000045585.77875.09. PMID15609827. S2CID14274035.
^Zimmerman R (2013). "Thamnophis sirtalis ". Kids' Inquiry of Diverse Species. Animal Diversity Web. Retrieved November 5, 2016.
^Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN978-1-4214-0135-5. (Thamnophis godmani, p. 102).
Conant R (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Boston: Houghton Mifflin Company. xviii + 429 pp. + Plates 1-48. ISBN978-0-395-19979-4 (hardcover), ISBN978-0-395-19977-0 (paperback). (Genus Thamnophis, p. 157).
Fitzinger L (1843). Systema Reptilium, Fasciculus Primus, Amblyglossae. Vienna: Braumüller & Seidel. 106 pp. + indices. (Thamnophis, new genus, p. 26). (in Latin).
Goin, Coleman J., Goin, Olive B.; Zug, George R. (1978). Introduction to Herpetology, Third Edition. San Francisco: W.H. Freeman and Company. xi + 378 pp. ISBN978-0-7167-0020-3. (Thamnophis, pp. 132, 156, 326).
Powell R, Conant R, Collins JT (2016). Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiv + 494 pp., 47 plates, 207 figures. ISBN978-0-544-12997-9. (Genus Thamnophis, p. 426).
Ruthven AG (1908). "Variation and Genetic Relationships of the Garter-snakes". Bulletin of the United States National Museum61: 1–201, 82 figures.
Schmidt, Karl P.; Davis, D. Dwight (1941). Field Book of Snakes of the United States and Canada. New York: G.P. Putnam's Sons. 365 pp., 34 plates, 103 figures. (Genus Thamnophis, p. 236).
Stebbins RC (2003). A Field Guide to Western Reptiles and Amphibians, Third Edition. The Peterson Field Guide Series. Boston and New York: Houghton Mifflin Company. xiii + 533 pp., 56 plates. ISBN978-0-395-98272-3. (Genus Thamnophis, pp. 373–374).
Vandenburgh J, Slevin JR (1918). "The Garter-snakes of Western North America". Proceedings of the California Academy of Sciences, Fourth Series8: 181–270, 11 plates.
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