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Garter snake ‒ also called gardener snake ‒ is the common name given to harmless, small to medium-sized snakes belonging to the genus Thamnophis. Endemic to North America, they can be found from the Subarctic plains of Canada to Central America. The garter snake is the state reptile of Massachusetts.
With no real consensus on the classification of species of Thamnophis, disagreement among taxonomists and sources, such as field guides, over whether two types of snakes are separate species or subspecies of the same species is common. Garter snakes are closely related to the genus Nerodia (water snakes), with some species having been moved back and forth between genera.
Garter snakes are present throughout most of North America. They have a wide distribution 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 populate a variety of habitats, including forests, woodlands, fields, grasslands, and lawns. They almost exclusively inhabit areas with some form of water, often an adjacent wetland, stream, or pond. This reflects the fact that amphibians are a large part of their diet.
Despite the decline in their population from collection as pets (especially in the more northerly regions in which large groups are collected at hibernation), pollution of aquatic areas, and introduction of 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, is an endangered subspecies and has been on the endangered list since 1969. Predation by crawfish has also been responsible for the decline of the narrow-headed garter snake (Thamnophis rufipunctatus).
Garter snakes, like all snakes, are carnivorous. Their diets consist of almost any creature they are capable of overpowering: slugs, earthworms, leeches, lizards, amphibians, ants, crickets, frog eggs, toads, minnows, and rodents. When living near water, they will eat other aquatic animals. The ribbon snake (Thamnophis sauritus) 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, because food can be scarce or abundant. Although they feed mostly upon live animals, they will sometimes eat eggs.
Coevolution of garter snakes and toxic newts
Tetrodotoxin is generally a lethal toxin that many organisms cannot take into their systems. Taricha granulosa has used this toxin as an imperative antipredator mechanism against the few predators that have the ability to prey upon them; the main predator being Thamnophis sirtalis. Theories about the evolution of the toxin within the newts include that of geographic location and the pure amount of predators in the area. Several other species have generated their own personal TTX resistance as well. Pufferfish are resistant to the toxin, allowing for them to carry it with them as a defense mechanism against predators that are TTX sensitive. Having this resistance also allows for them to prey upon other species that also contain the toxin. However, there are no known predators of pufferfish. This shows that coevolution does not always exist and that it is a complex occasion in which there has to be coexisting species capable of competing. In order to see the genetic basis of TTX resistance in pufferfish, a species other than garter snakes, researchers sequenced the proteins of the skeletal muscle sodium channels. This showed that just like garter snakes, pufferfish have substitutions in the pore (P) loop regions of the four domains. Some substitutions in the P loop of domain one in the nonaromatic amino acid residues of cysteine and asparagine were found to be linked to TTX resistance. In garter snakes the reason behind the resistance lies within the mutations in the outer pore of domain four of the sodium channels.
One experiment found that there is indeed a clear link between the ecology of the newts and garter snakes. In one experiment, TTX extracts were taken from seventeen adult newts were collected from six separate sites. These samples were then filtrated and used to analyze the TTX levels per population. In this study, they found that some of the newt populations did not contain any traces of TTX while all of the others did. It also aided the theory of coevolution between these newts and garter snakes in that variation among these toxin levels per location is needed. The experiment also showed geographic variation of the populations that support the theory that as newts increase the production of TTX, garter snakes evolve to have greater resistance to the toxin. In the areas that the non-toxic newts were found, garter snakes lacked any resistance. However, in the areas where newts had high levels of tetrodotoxin, the garter snakes possessed a greater resistance to the toxin. Different levels of TTX production and resistance between populations follows the geographic mosaic perspective of coevolution since it varies between populations in different location.
In a separate experiment, scientists collected sixty-eight sets of data on a similar species of TTX resistant garter snakes (Thamnophis couchii). These specimens were then analyzed for their resistance to TTX through a bioassay of their overall performance. After injection they were analyzed based upon their initial baseline speed. The data collected from the analysis showed that this species of snake had a high resistance to TTX and there was a tradeoff between locomotive performance and resistance. The researchers found that the snakes that moved the slowest post-injection were the most resistant compared to the faster moving ones. A newt species (Taricha torosa) similar to that of the previous experiment were collected and tested for TTX levels. It was found that each of them contained various levels of the toxin based upon their size. As the newt grows larger, they are capable of having more of the toxin in their glands. Within the study, it was found that the species Thamnophis couchii would be able to ingest most adult Taricha torosa without becoming fully impaired, but if the species Thamnophis sirtalis were to eat the same newts, they would not have any locomotive functions. This displayed the theory that specific predator species within an environment will be resistant enough relative to the sympatric species of prey they are consuming. Not only does this occur, but it also fits hand in hand with the Red Queen hypothesis in the sense that there is always a footrace between the species of garter snakes and newts. It has been shown through this experiment and ones from years ago that these two species are coevolving. As the newts become more toxic, the garter snakes respond and evolve to be more resistant.
An experiment comparing the effects of interpopulation and interspecific variation in tetrodotoxin resistance discovered differences between them. This research included sympatric Thamnophis sirtalis that coexists with Taricha granulosa, allopatric Thamnophis sirtalis that does not coexist with Taricha granulosa, and sympatric Thamnophis ordinoides. It was discovered that no matter what the dosage of TTX, the sympatric Thamnophis sirtalis showed much less reduction in motor skills than the other populations. When given concentrations of 0.00015mg of TTX, this grouping showed little to no effects while the other two groupings were reduced to less than twenty percent of their baseline speed. This study showed that TTX resistance is not a trait of the genus Thamnophis or the species sirtalis, but it is adaptation of populations that coexist with the toxic prey. The main influence of the intake of the toxin and the exposure length of the snakes to the toxin is the snake’s ability to recognize its own resistance level. An unknown mechanism in which the snakes know how much toxin they can handle allows for them to either reject the newt or to ingest the newt.
Garter snakes have complex systems of pheromonal communication. 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 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. 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.
If disturbed, a garter snake may coil and strike, but typically it will hide its head and flail its tail. These snakes will also discharge a malodorous, musky-scented secretion from a gland near the cloaca. 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, raccoons, crayfish, and other snake species (such as the coral snake and king snake) will eat garter snakes, with even shrews and frogs eating the juveniles.
Being heterothermic, like all reptiles, garter snakes bask in the sun to regulate their body temperature. During hibernation, garter snakes typically occupy large, communal sites called hibernacula. These snakes will migrate large distances to brumate.
Garter snakes go into brumation before they mate. They stop eating for about two weeks beforehand to clear their stomachs of any food that would rot there otherwise. Garter snakes begin mating as soon as they emerge from brumation. During mating season, the males mate with several females. In chillier parts of their range, male common garter snakes awaken from brumation first, giving themselves enough time to prepare to mate with females when they finally appear. Males come out of their dens and, as soon as the females begin coming out, surround them. Female garter snakes produce a sex-specific pheromone that attracts male snakes in droves, sometimes leading to intense male to male competition and the formation of mating balls of up to 25 males per female. After copulation, a female leaves the den/mating area to find food and a place to give birth. Female garter snakes are able to store the male's sperm for years before fertilization. The young are incubated in the lower abdomen, at about the midpoint of the length of the female's body. Garter snakes are ovoviviparous, meaning they give birth to live young. However, this is different from being truly viviparous, which is seen in mammals. Gestation is two to three months in most species. As few as three or as many as 80 snakes are born in a single litter. The young are independent upon birth. On record, the greatest number of garter snakes reported to be born in a single litter is 98.
Garter snakes in captivity
T. sirtalis, T. marcianus and T. sauritus are the most popular species of garter snakes kept in captivity. Baby garter snakes shed their first skin almost immediately, and will begin eating soon after. Garter snakes just require a 10 gallon (38 liter) terrarium. The first shedding is very fine and often disintegrates in minutes under the slithering masses of new snakes. Feeding baby garter snakes can be tricky; earth worms (not compost worms), night crawlers (called dew worms in Canada), silversides (fish), or cut up pieces of pinky mice (thawed fully and waved before the snake on a pair of tongs or hemostats to avoid nipping fingers) will entice appetites. Up to 10 days may pass before a baby garter snake eats; it takes them some time to become accustomed to new settings.
Garter snakes were long thought to be nonvenomous, but recent discoveries have revealed they do, in fact, produce a mild neurotoxic venom. Garter snakes cannot kill humans with the small amounts of comparatively mild venom they produce, and they also lack an effective means of delivering it. They do have enlarged teeth in the back of their mouths, but their gums are significantly larger. The Duvernoy's gland of garters are posterior (to the rear) of the snake's eyes. The mild venom is spread into wounds through a chewing action.
Species and subspecies
- Longnose garter snake, T. angustirostris (Kennicott, 1860)
- Aquatic garter snake, T. atratus
- Shorthead garter snake, T. brachystoma (Cope, 1892)
- Butler's garter snake, T. butleri (Cope, 1889)
- Goldenhead garter snake, T. chrysocephalus (Cope, 1885)
- Western aquatic garter snake, T. couchii (Kennicott, 1859)
- Blackneck garter snake, T. cyrtopsis
- Western blackneck garter snake, T. c. cyrtopsis (Kennicott, 1860)
- Eastern garter snake, T. c. ocellatus (Cope, 1880)
- Tropical blackneck garter snake, T. c. collaris (Jan, 1863)
- Tepalcatepec Valley garter snake, T. c. postremus H.M. Smith, 1942
- Yellow-throated garter snake, T. c. pulchrilatus (Cope, 1885)
- Western terrestrial garter snake, T. elegans
- Arizona garter snake, T. e. arizonae V. Tanner & Lowe, 1989
- Mountain garter snake, T. e. elegans (Baird & Girard, 1853)
- Mexican wandering garter snake, T. e. errans H.M. Smith, 1942
- Coast garter snake, T. e. terrestris Fox, 1951
- Wandering garter snake, T. e. vagrans (Baird & Girard, 1853)
- Upper Basin garter snake, T. e. vascotanneri W. Tanner & Lowe, 1989
- Sierra San Pedro Mártir garter snake, T. e. hueyi Van Denburgh & Slevin, 1923
- Thamnophis eques
- Mexican garter snake, T. e. eques (Reuss, 1834)
- Laguna Totolcingo garter snake, T. e. carmenensis Conant, 2003
- T. e. cuitzeoensis Conant, 2003
- T. e. diluvialis Conant, 2003
- T. e. insperatus Conant, 2003
- Northern Mexican garter snake, T. e. megalops (Kennicott, 1860)
- T. e. obscurus Conant, 2003
- T. e. patzcuaroensis Conant, 2003
- T. e. scotti Conant, 2003
- T. e. virgatenuis Conant, 1963
- Montane garter snake, T. exsul Rossman, 1969
- Highland garter snake, T. fulvus (Bocourt, 1893)
- Giant garter snake, T. gigas Fitch, 1940
- Godman's garter snake, T. godmani (Günther, 1894)
- Two-striped garter snake, T. hammondii (Kennicott, 1860)
- Checkered garter snake, T. marcianus (Baird & Girard, 1853)
- T. m. marcianus (Baird & Girard, 1853)
- T. m. praeocularis (Bocourt, 1892)
- T. m. bovalli (Dunn, 1940)
- Blackbelly garter snake, T. melanogaster
- Tamaulipan montane garter snake, T. mendax Walker, 1955
- Northwestern garter snake, T. ordinoides (Baird & Girard, 1852)
- Western ribbon snake, T. proximus
- Chiapas Highland western ribbon snake, T. p. alpinus Rossman, 1963
- Arid land western ribbon snake, T. p. diabolicus Rossman, 1963
- Gulf Coast western ribbon snake, T. p. orarius Rossman, 1963
- Western ribbon snake, T. p. proximus (Say, 1823)
- Redstripe ribbon snake, T. p. rubrilineatus Rossman, 1963
- Mexican ribbon snake, T. p. rutiloris (Cope, 1885)
- Plains garter snake, T. radix (Baird & Girard, 1853)
- Rossman's garter snake, T. rossmani Conant, 2000
- Narrowhead garter snake, T. rufipunctatus
- Ribbon snake, T. sauritus
- Longtail Alpine garter snake, T. scalaris (Cope, 1861)
- Short-tail Alpine garter snake, T. scaliger (Jan, 1863)
- Common garter snake, T. sirtalis
- Red-spotted garter snake, T. s. concinnus (Hallowell, 1852)
- New Mexico garter snake, T. s. dorsalis (Baird & Girard, 1853)
- Valley garter snake, T. s. fitchi Fox, 1951
- California red-sided garter snake, T. s. infernalis (Blainville, 1835)
- T. s. lowei W. Tanner, 1988
- Maritime garter snake, T. s. pallidulus Allen, 1899
- Red-sided garter snake, T. s. parietalis (Say, 1823)
- Puget Sound garter snake, T. s. pickeringii (Baird & Girard, 1853)
- Bluestripe garter snake, T. s. similis Rossman, 1965
- Eastern garter snake, T. s. sirtalis (Linnaeus, 1758)
- Chicago garter snake, T. s. semifasciatus (Cope, 1892)
- San Francisco garter snake, T. s. tetrataenia (Cope, 1875)
- Sumichrast's garter snake, T. sumichrasti (Cope, 1866)
- West Coast garter snake, T. valida
- Mexican Pacific Lowlands garter snake, T. v. celaeno (Cope, 1860)
- T. v. isabellae Conant, 1953
- T. v. thamnophisoides Conant, 1961
- T. v. valida (Kennicott, 1860)
- Wright, A.H. & A.A. Wright. (1957). Handbook of Snakes of the United States and Canada. Comstock. Ithaca and London. p. 755.
- "Citizen Information Service: State Symbols". Massachusetts State (Secretary of the Commonwealth). Retrieved 2011-01-21.
The Garter Snake became the official reptile of the Commonwealth on January 3, 2007.
- Brodie, Edmund D., III, Chris R. Feldman, Charles T. Hanifin, Jeffrey E. Motychak, Daniel G. Mulcahy, Becky L. Williams, and Edmund D. Brodie, Jr. (2005). Parallel Arms Races between Garter Snakes and Newts Involving Tetrodotoxin as the Phenotypic Interface of Coevolution. Journal of Chemical Ecology 31: 343-356.
- Soong, Tuck W., and Byrappa Venkatesh (2006). Adaptive Evolution of Tetrodotoxin Resistance in Animals. ScienceDirect. 22(11): 621-626.
- Venkatesh, Byrappa, Song Qing Lu, Nidhi Dandona, Shean Long See, Sydney Brenner, and Tuck Wah Soong. (2005). Genetic Basis of Tetrodotoxin Resistance in Pufferfishes. Current Biology' 15(22):2069-2072.
- Brodie, Edmund D., III, and Edmund D. Brodie, Jr. (2008). Tetrodotoxin Resistance in Garter Snakes: An Evolutionary Response of Predators to Dangerous Prey. Society for the Study of Evolution 44: 651-659.
- Williams, Becky L., Edmund D. Brodie, Jr., and Edmund D. Brodie, 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.
- Shine R, Phillips B, Waye H, LeMaster M, Mason RT. (2001). Benefits of female mimicry to snakes. Nature 414:267. doi:10.1038/35104687
- "Garter Snake Care Sheet". Thamnophis.com.
- Zimmer, Carl (April 5, 2005). "Open Wide: Decoding the Secrets of Venom". The New York Times.
- Beolens B, Watkins M, Grayson M. 2011. The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN 978-1-4214-0135-5. (Thamnophis godmani, p. 102).