The Giant garter snake (Thamnophis gigas ) is the largest species of garter snake. Relatively rare, it is a semi-aquatic venomous snake with a limited distribution in the wetlands of central California.
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DiurnalDiurnal animals are active during the daytime, with a period of sleeping or other inactivity at night. The timing of activity by an animal depends ...
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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PrecocialPrecocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. Precocial species are normall...
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SemiaquaticSemiaquatic animals are those that are primarily or partly terrestrial but that spend a large amount of time swimming or otherwise occupied in wate...
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BrumationBrumation is a lethargic state that some ectothermic animals, such as many reptiles, assume during cold conditions. Reptiles generally begin brumat...
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OvoviviparousOvoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous an...
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PredatorPredators are animals that kill and eat other organisms, their prey. Predators may actively search for or pursue prey or wait for it, often conceal...
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VenomousVenom is a type of poison, especially one secreted by an animal. It is delivered in a bite, sting, or similar action. Venom has evolved in terrestr...
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withAs with many snakes, the female Giant garter snakes tend to be longer and larger than the males. These snakes have keeled scales, with a yellow dorsal stripe against a black or dark grey background, and two additional yellow stripes on either side that run the length of their body. Although, some unstriped checkered patterns have been observed.
Giant garter snakes are found in Central California. Their historic range extends through much of Central California's Sacramento and San Joaquin valleys but has been reduced to a few fragmented areas in the Sacramento Valley. Due to their semiaquatic nature, these snakes are rarely found more than a few meters from water during the active season. They historically inhabited wetland habitats, particularly tule marshes, but due to the destruction of these habitats, they are now predominantly found in artificial wetlands associated with rice agriculture. Giant garter snakes prefer stagnant or slow-moving water bodies with emergent vegetation; they use water to thermoregulate and deep and fast-moving water bodies are too cold, while emergent vegetation protects them from predators.
Giant garter snakes are active during the day from spring to late fall. Highly aquatic, they are active when water temperatures are at 68 °F (20 °C) or more. Despite their dependence on water, Giant garter snakes spend most of their time on land during the active season and all their time in brumation on land during the winter. When not underground, they seek litter or vegetation (particularly tules) to use as cover from predators and environmental extremes, and they avoid rocky or otherwise open areas. Like other garter snakes, the Giant garter snake can release a foul-smelling musk from its cloaca if it feels threatened or disturbed. Although these snakes are venomous, they are harmless to humans; they have a very mild neurotoxic venom that helps subdue their prey. A bite to a human will at most give a red itchy rash around the area of the bite.
Giant garter snakes are carnivores and hunt aquatic prey such as fish, frogs, and tadpoles. Adult snakes commonly eat bullfrog juveniles and tadpoles.
From March to mid-May, male giant garter snakes emerge from hibernation searching for a female to mate with. Because Giant garter snakes hibernation dens are typically more spread out compared to other garter snakes, males must expend more energy to find a potential mate. These snakes are ovoviviparous, meaning they carry eggs internally but give live birth. Following the spring mating season, birthing occurs from mid-July to early October with an average litter size of 17 young. The snakelets are born fully developed and are able to feed and survive independently. Young females become reproductively mature at 5 years of age, while males are ready to breed when they are 3 years old.
The main threat to the Giant garter snake is the destruction of its native habitat. The species has been extirpated from 98% of the former San Joaquin habitat. In addition to habitat loss and fragmentation, introduced predators such as the American bullfrog and the Northern water snake may also threaten the Giant garter snake.
The IUCN Red List and other sources don’t provide the number of the Giant garter snake total population size. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List, and its numbers today are decreasing.
