Reptilia · Squamata
Thamnophis atratusKennicott, 1860
Santa Cruz Garter Snake
Photograph by Roger Raiche, CC BY, via iNaturalist
A water-living, day-active, meat-eating snake from the Nearctic region, reaching 107 cm nose to tail.
Also called Pacific Coast Aquatic Garter Snake.
Reptilia › Squamata › Colubridae › Thamnophis
- Grows to
- 1070mm
- greatest recorded
- Eats
- Carnivorous
- Active
- Diurnal
- Lives up to
- 7.8years
Longer than 74% of all colubrid snakes anyone has measured.
The bar is the rank itself: its length is the share of the family this animal exceeds. The chart below is the family’s real spread, on a logarithmic scale because body length here runs from 98 to 3,800 mm. The solid rule is this animal. Every bar is a count of real species, and nothing on this figure is estimated.
What is known
36 sourced facts, each taken from a named scientific dataset. How to read these.
Cited from a dataset unless a row is marked otherwise.
Standing in the world
- Still living
- Extant
- Conservation status
- Least Concern
- Status assessed · the year the Red List last looked
- 2007
- Population trend
- Stable
The animal itself
- Limbs
- None
- Pupil
- Round
- Venomous
- Yes
- Fangs
- At the back of the mouth
- Longest recorded life
- 7.8years
- Body temperature when active · measured in the wild
- 15.16°C59 °F
- Body temp in the wild · mean, when active
- 9–35°C48–95 °F
mean body temperature of active individuals in nature
body temperature of active animals in nature
Size
- Length nose to tail · greatest recorded
- 1070mm3 ft 6 in
- Hatchling length · snout to vent
- 99.75mm4 in
- Body mass · greatestcomputed
- 298.6g10.5 oz
- Body mass at hatchingmeasured
- 1.58g0.06 oz
snakes only in this source
1070 mm total length (Feldman et al. 2016), Rossman et al. 1996 (neonate SVL 99.1-100.4 mm)
computed from length by a family-level allometric equation, not weighed
How it lives
- Dietcomputed
- Carnivorous
- How it hunts
- Active foraging
- Active
- Diurnal
- Where it lives
- Aquatic
- Habitat
- Forest, Grassland, Shrubland
- Biome
- Temperate Coniferous Forests
- Region
- Nearctic
- Mainland or island
- Mainland
- Highest it lives · above sea level
- 1920m
- Range size
- 115,513km²
no actual data but can be imputed as carnivorous like all snakes
Active (Feldman 2015)
Feldman 2015
(Feldman 2015), Semi-Aquatic (Deepak et al. 2022)
0-1920 (Feldman 2015)
Breeding
- Reproduction
- Viviparous
- Average clutch
- 8.5eggs
- Eggs or young per clutch
- 7–9eggs
- Mean clutch
- 7.8–8.5eggs
Feldman et al. 2015
mean 8.5 (Meiri et al. 2019), means 7.8-8.4 (Rossman et al. 1996)
Naming and history
- Suborder
- Serpentes
- Infraorder
- Alethinophidia
- Subspecies
- Thamnophis atratus atratus (KENNICOTT 1860) Thamnophis atratus hydrophilus FITCH 1936 Thamnophis atratus zaxanthus BOUNDY 1999
- Described by
- Kennicott
- Moved to another genus · since it was first described
- No
- Described in
- 1860
- Type locality
- USA
Keeping one
3 ft 6 in × 21 in × 2 ft 8 in(107 × 54 × 80 cm)
Minimum length × width × height, for one animal. Bigger is always better.
The standard sizes snakes as a fraction of total length: 1 × 0.5 × 0.75.
Spends time in water, so a water area is part of the enclosure rather than a dish.
Mindestanforderungen an die Haltung von Reptilien (Sachverständigengutachten), German Federal Ministry for Nutrition, Agriculture and Forestry, Animal Welfare Division, 10 January 1997. The standard states these floor areas are recommendations rather than binding limits.
From this animal’s own total length of 3 ft 6 in (1070 mm), at 1 × 0.5 × 0.75 times it, following the German federal welfare standard — how this is worked out.
Active animals measured in the wild averaged 59 °F (15.2 °C).
Mean body temperature of active individuals measured in nature. A measurement of the animal, not a setting for a thermostat.
Feeding
A prey item should be between the same width as the widest part of the snake's body and about 1.5 times that width.
Widely used across snake husbandry references. An alternative formulation gives prey at 10-15% of the snake's body mass. This is established practice, not a measurement.
31kJ per day
Worked out for an animal of 299 g, the heaviest recorded for Santa Cruz Garter Snake — so it is the top of the range, not a figure for a particular animal. Weigh yours and the number will be lower.
An upper estimate, not a feeding target, and not veterinary advice. The equation covers only what an animal burns staying alive, so a growing, gravid or recovering animal needs more — and it was measured on wild animals, which move far more than one in an enclosure. Body condition and a vet who knows the species are what a feeding decision should rest on. Where this comes from.
What nobody knows
These are not gaps in our research. No scientific dataset records them for this species — and saying so is information you cannot get from a reference that simply leaves a field out.
- — Length snout to vent · greatest recorded
- — Length snout to vent · adult female mean
- — Length snout to vent · adult male mean
- — Length snout to vent · adult mean
- — Female length · mean, nose to tail
- — Length nose to tail · adult male mean
- — Length nose to tail · adult mean
- — Largest female · snout to vent
- — Largest male · snout to vent
- — Largest female · shell length
- — Largest male · shell length
- — Hatchling length · nose to tail
- — Largest juvenile · snout to vent
- — Largest juvenile · shell length
- — Egg length
- — Egg width
- — Body mass · a typical adult
- — Body mass · adult female, mean
- — Preferred body temperature · chosen in a laboratory gradient
- — Eats arthropods
- — Eats vertebrates
- — Eats plant matter
- — How the young develop
- — Gestation or incubation
- — Clutches in a year
- — Clutches a year · fewest
- — Clutches a year · most
- — First breeds from · youngest recorded
- — First breeds by · oldest recorded
- — Hatchling length · smallest recorded
- — Hatchling length · largest recorded
- — Age at first breeding · female
- — Mature from · youngest recorded
- — Mature by · oldest recorded
- — Size at maturity · smallest recorded
- — Size at maturity · largest recorded
- — Colour on the back
- — Pattern on the back
- — Sex decided by
- — Red List criteria
- — Active season · shortest recorded
- — Active season · longest recorded
- — Density · lowest recorded
- — Density · highest recorded
- — Home range · largest recorded
- — Active in
- — Lowest it lives · above sea level
Others in Colubridae
Take this data
Everything on this page is available as data under CC BY 4.0 — use it freely, credit it, no permission needed.
This species as JSON · the whole dataset
Cite this page
The Reptile & Amphibian Encyclopedia (2026). Thamnophis atratus. Retrieved 2026-09-08, from https://www.allanglescreatures.com/species/thamnophis-atratus
@misc{thamnophis_atratus_2026,
title = {Thamnophis atratus},
author = {{The Reptile & Amphibian Encyclopedia}},
year = {2026},
url = {https://www.allanglescreatures.com/species/thamnophis-atratus}
}Sources
- Meiri, S. (2024). SquamBase — a database of squamate (Reptilia: Squamata) traits. Global Ecology and Biogeography. Public domain (CC0).
- Oskyrko, O. et al. (2024). ReptTraits: a comprehensive dataset of ecological traits in reptiles. Scientific Data. Used under CC BY 4.0.
- Catalogue of Life (dataset 3LR), used under CC BY.