Thamnophis elegans terrestris: the Coast Garter Snake (red morph)


Coastal dunes in Marin County: typical habitat T.e.terrestris red morph.

The Western Terrestrial Garter Snake (Thamnophis elegans) occurs in western USA, in Western Canada and just a small area in Baja California, Mexico. It was not until 1979 that this species was recognized as a separate species. It is an intriguing species that sometimes wanders far away from water and can be quit terrestrial, hence the name Western Terrestrial Garter Snake.

Six subspecies are recognized by Rossman, Ford & Siegel(1996) but currently I only keep the Coast Garter Snakes (Thamnophis elegans terrestris).

Length and size of Thamnophis elegans terrestris

Adult male (nr.37, captive bred) 4 years old from mountain population San Mateo County.Maximum length of T.elegans according to literature (Rossman, Ford & Siegel, 1996) is 107,0 cm.
This length  is probably very exceptional and maybe this size is measured in another subspecies. Adult females Thamnophis elegans terrestris can reach 80 – 90 cm total length but the males are much smaller and thinner (60 – 80 cm total length). The maximum size I have seen are those in my own collection: a female of 87 cm and a male of 77 cm.

Especially the females are relatively heavy build and stoutbodied with large heads. The males are usually much thinner.

Description of Thamnophis elegans terrestris (“red morph”)

Adult female from mountain population San Mateo County.

Adult female from mountain population San Mateo County.

T.e.terrestris typically has three yellow stripes and the amount of red on the body and belly varies. The head normally has little red, although orange red spots may occur.

The vertebral stripe is often very bright yellow, almost like it is shining. The lateral stripes are often less conspicuous.

Often they are yellow, but in some populations they are completely orange-red colored. In between the stripes there is usually a double row of alternating spots that can vary in size. The ground color between the stripes varies from very pale light brown, dark brown, almost black, dull red to bright red.

Adult female from mountain population San Mateo County.In most specimens of T.e.terrestris I have observed in San Mateo County and Marin County there is some red or a lot of red visible between the stripes.
In general the red coloration is most conspicuous above the lateral stripe and it gets less towards the vertebral stripe.

The belly can be pale with a few red spots, but the red spots may be so dominant that it turns the belly practically completely red.
Adult male from mountain population San Mateo County.It is not very clear from literature if there are areas where T.e.terrestris is more red, more black or more brown or whether all color morphs occur  all over the range. My personal observations in San Mateo County and Marin County suggest that all terrestris from this area could be called “red morph” although it intensity varies a lot.

For instance in one population of T.e.terrestris where they occur together with T.s.tetrataenia the amount of red was very vivid and bright. They were competing with T.s.tetrataenia to be the most vividly colored snakes.


Adult male (nr.37, captive bred) 4 years old from mountain population San Mateo County exploring the area.Similar to the sympatric Thamnophis atratus atratus this diurnal snake is most of the time clearly visible in its terrarium showing its gorgeous red coloration.. Basking on a hot spot on a branch or on the ground.

Normally they are not problematic eaters and they can be quit voracious. Both fish and (baby) mice are readily accepted. Mice and even small birds (nestling) can be  a very normal prey of the adult snakes in the wild. As far as breeding and care in captivity is concerned the basics are provided in the article I wrote on Thamnophis atratus atratus (see Bol, 2007 under Publications).

Distribution and habitat of Thamnophis elegans terrestris

Map California Central Valley


T.e.terrestris occurs in a narrow coastal strip from the southern part of California up until southern Oregon.
Hence the common name “Coast garter Snake”.

I have found this subspecies always relatively close to small rivers, ponds, marshes or sloughs although literature states that they can live far away from water and be very terrestrial.


My Publication about Thamnophis atratus atratus (Bol,2007) can serve as a good guideline for keeping and breeding  the Coast Garter Snake.

Breeding group

Habitat of the mountain population of T.e.terrestris from San Mateo County; the lake in July.

Habitat of the mountain population of T.e.terrestris from San Mateo County; the lake in July.

My breeding Group consists of snakes originating from 2 different populations with different coloration and pattern.

One Group consists of snakes from a population that lives in the hills of San Mateo County. They can be found, together with T.a.atratus near the edges of a small lake at 610 meters above sea level. Most snakes from this population are quit dark with a very bright dorsal stripe. The belly tends to be strongly red colored and this red coloration is also profound on the side going up towards the dorsal stripe. This results in many specimens having a beautiful red or pinkish lateral stripe.

Some observations made in May 2000 on this population are described in Bol (2002).

Adult male (nr.37, captive bred) 4 years old from mountain population San Mateo County; underside belly.This population differs a lot from the more coastal population and in fact resemble T.s.sirtalis “flame” a lot in general appearance.Because of the southern latitude it can be quit warm in spring, summer and even fall,  but at the same time this habitat is strongly influenced by the cold waters of the pacific ocean. The coastal areas in California are often covered in fog (“marine layer”) and under these circumstances day temperatures Coastal strip is often shrouded in mist.sometimes do not rise above 16 ºC even in mid summer in a narrow coastal strip. A few kilometers away from the ocean the sun sometimes can burn away the fog and temperatures rise to 30 plus ºC. I expect that this population hibernates for at least 3 – 5 months. This is based on my observations done in February, March, April and May. I mostly found them less then 2 meter from the edge of the lake.

Coastal dunes in Marin County: typical habitat T.e.terrestris red morph.

Coastal dunes in Marin County: typical habitat T.e.terrestris red morph.

My second breeding groups originates from snakes from the coastal dunes of San Mateo County and Marin County. These marshy habitats are located just behind the beach. This habitat will even be more influenced by the Cold Pacific ocean then the population inhabiting the hills. Temperatures in June, July and August sometimes do not exceed the 12 – 16º C maximum for weeks in row (personal observation). In these marshes  the dominant Thamnophis elegans terrestris shares the habitat with Thamnophis atratus atratus , T.a. intergardes, T.sirtalis tetrataenia  and T.s.infernalis. Snakes from the coastal dunes are definitely not as dark as the snakes from the mountain population.

Baby snake 2 month old from mountain population San Mateo County; first signs of red on the sides.Normally all the stripes are clearly yellow without the red color invading. Between the stripes the snakes are red with normally 2 rows of back spots.
Some specimens are extremely red (except the double row of dark spots) between the stripes.

Nice detail, when the snakes are born they lack any trace of red. After a few months some red coloration starts to become visible and it takes at least 1-2 years before the snakes will have their final colors.

Bol, S., 2002. Observations on Thamnophis atratus atratus and Thamnophis elegans terrestris in San Mateo County, California. The garter snake 7 (2): 3-8.
Bol, S., 2007.  Verzorging en kweek van de Santa Cruz Kousebandslang Thamnophis atratus atratus. Lacerta 65(5): 200-217
Rossman, D.A., N.B.Ford & R.A.Siegel, 1996. The Garter Snakes. Evolution and ecology. University of Oklahoma Press, Norman
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