Breeding and care in captivity of the Santa Cruz Garter Snake (Part 1)

Breeding and care in captivity of the Santa Cruz Garter Snake, Thamnophis atratus atratus (Kennicott, 1860).

Steven Bol (Author…)


T.a.atratus, adult female of about 80 cm, San Mateo County, Ca.Garter snakes are very attractive and active snakes. This North American genus has many species (30 according to Rossman, Ford & Siegel, 1996) that occur from Canada to the middle of America (Honduras, El Salvador).  The variation in pattern, colour, build and ecology are enormous.

The most well known, most held and imported species is the Common or Eastern garter snake Thamnophis sirtalis, of which the very rare subspecies that occurs in a very small area around San Francisco (Thamnophis sirtalis tetrataenia) is world-famous. Less known but also very attractive are two species that occur more or less sympatric with the San Francisco Garter Snake (T.s.tetrataenia) in San Mateo County in CaliforniaThamnophis elegans terrestris, the West Coast Garter Snake and Thamnophis atratus atratus, the Santa Cruz Garter Snake.

T.elegans terrestis from San Mateo County, Ca.It is almost incredible that in the same area three such beautiful species of garter snakes occur simultaneously.  In this article, I want to describe my experiences with the care in captivity and the breeding of the Santa Cruz Garter Snake.

This species flourishes very well in captivity and is therefore very suitable for as well the beginning as the more experienced hobbyist.  I hope that this article will make more people enthusiastic about this rarely kept species of garter snake and that it can serve as a guideline how to keep this species successful in captivity and how to breed it.

Keeping records of measurements of the adults, timing of birth, clutch and number size etc. can generate valuable data (see the request for additional data in Rossman, Ford & Siegel, 1996) on the reproductive biology of garter snakes. In this way hobbyists can help herpetologists to interpret the data collected in the wild. In this article data on the reproductive biology of Thamnophis atratus atratus collected over the past 6 years are presented and analysed.


Big pregnant female T.a.atratus of 85 cm, beautiful orange-yellow spinal, San Mateo County, Ca.Thamnophis atratus is a relatively large species of garter snake, that reaches a maximum length of 101.6 cm (Rossman, Ford & Siegel, 1996), but the average length of the adult snakes is approximately 60 – 80 cm.  It was only in 1987 that Thamnophis atratus was recognized as a separate species. In older literature this species, together with other west coast species, was treated as a subspecies or synonym of the “catchall taxa” Thamnophis elegans, ordinoides or couchii (Rossman, Ford & Siegel, 1996). There is quit a lot of variation in pattern and colour within this species. Rossman, Ford & Siegel (1996) distinguish 2 subspecies: Thamnophis atratus atratus and T. a. hydrophilus. My animals belong to the subspecies T. a. atratus and originate from a population of which the ground colour is quite dark (nearly black) with 1 beautiful and very contrasting yellow (pale  yellow to warm orange yellow) middorsal stripe and a yellow throat.  Some specimens of Thamnophis atratus have 3 stripes.  Recently a new subspecies has been described:  T.a.zaxanthus ( Thamnophis atratus atratus is quite heavily build and especially the adult women can become large. For an extensive description, I refer to the magnificent book of Rossman, Ford & Siegel (1996) and the website mentioned above.

Habitat and distribution

Biotope of T.a.atratus and T.elegans terrestris in San Mateo County, California.Rossman, Ford & Siegel (1996) give the following description of the habitat of Thamnophis atratus: shallow, rocky creaks and swift-flowing streams in dense-canopy oak woodlands woods and grassy woodland ecotones. When they occur in ponds with muddy bottom there are generally rocky outcrops in the vicinity. Open basking areas along the river banks are very important. The species occurs along the coastal area of southern Oregon in the north to the middle of California (Santa Barbara County) in the south. Personal observations on this highly aquatische species in their natural habitat have been described in Bol (2002).

The terrarium

As a minimum requirement for the size of the terrarium to keep 1 or 2 adult couples of this species I recommend 65 x 50 x 50 cm (L x W x H). I have kept these snakes in both all-glass as wooden (with a glass front) terrarium.

For the proper care of this species some things need extra attention.

  • The terrarium must be well ventilated, the land part must be completely dry and the right temperature range must be created.
  • For ventilation I use generous strips of wire mesh in the lid (asymmetrical) with a maximum of  20% of the surface.
  • Although the snakes are highly aquatic they should certainly not be kept in a damp and moist environment. The bottom surface is usually filled with beech woodchips. The water bowl consists normally of less then 1/6 of the bottom surface. The land part of the terrarium must be kept completely dry. Spraying water to mimic rainfall will certainly be no problem, although I rarely do so. Keeping the snakes in a too damp cage can easily cause skin problems. The water part consists of an earthenware or plastic bin, so that the land and water area is completely separated
  • In order to make the interior of the terrarium more attractive and natural I use stumps, branches to climb, boulders etc. I give the snakes always the possibility to hide themselves. In a corner of the terrarium I put some leaf litter or pruned conifers branches from the garden for an extra natural effect and hiding place. Plants I do not use (anymore).
  • The terrarium gets cleaned and disinfected at least 1 – 2 per year. This species will probably thrive in a natural habitat terrarium with a large water bowl in which one offer can live fish.
  • For heating and illuminating the terrarium I use a light bulb (normal or reflected) of 15 – 75 Watt depending on the snake room temperature. The bulb is placed in a corner of the terrarium and some branches allow the snakes to bask right under the bulb. I always try to create a temperature range with a warm corner of at least 30 – 35 °C and a cool corner of 20 – 24 °C  during daytime. The combination of ample ventilation (asymmetrical), sufficient terrarium volume (not too small or too low) and a light bulb high in the least ventilated corner of the terrarium automatically creates a temperature range!
  • Noteworthy is the fact that all of my terrariums are placed in a not-heated attic room.  In the winter months the temperature in this room fluctuates from 8 – 12 °C during night time and to 10 – 15 °C during daytime. When outside temperatures rise the snake room temperatures rise as well. During summertime temperatures can rise up to at least 30 °C and higher.
  • In the beginning of 2005 I started to use a thermostat that shuts down the bulbs (and the heating inside the terrariums) as soon as the room temperature rises above a particular threshold. As threshold I mostly use 24 – 26 °C, in order to prevent that the temperature in the terrarium rises too far. Before 2005 this was regulated by “gut feeling”; when warm summer days were expected I shut down all lighting/heating early morning (see “problems and illnesses”).
  • Except during the hibernation period (see hibernation) the bulbs are switched on from 8 AM until 9 PM with little variation of the “day length” during the season. At nights all lights (heating) are shut off which causes the terrarium temperature to drop to the snake room temperature:  10 – 12 °C in the early spring (February/March /April) to 18 – 25 °C during the warmer months of the year.

Adult male T.a.atratus of 73 cm, beautiful orange-yellow spinal, San Mateo County, Ca.Preferred body temperatures of most garter snakes are estimated somewhere between 26 – 32 °C (Rossman, Ford & Siegel, 1996), and a temperature range allows snakes to regulate their own body temperature just like in the wild.
Observing the behaviour of the snakes also can gives you indications whether you have created the right temperature range: when T.a.atratus does not bask on the warm spot and hides itself is the whole day then the temperature is most likely too cold (and they sort of expand the hibernation period in the heated terrarium) or too hot (so they look for the coolest place in the terrarium which is most likely ion the coolest corner under rocks or debris).
The ideal behaviour I like to observe is that within 1 – 2 hours after the bulbs are switched on the snakes will start basking on the warm spot and later during the day they will continue basking a little further away from the hot spot or even totally hide themselves. This observation combined with regular feeding behaviour of the snakes and a cool spot which not warmer than 25 – 28 °C maximum (colder is not problem)gives me the conviction that I have created the right temperature range. In my experience T. a. atratus is a species that likes relative high temperatures and I have the impression that their preferred body temperature may even be slightly higher then 32 °C.
I have seen the snakes, especially in early spring, basking on the hottest spot in the terrarium and it was not until the temperature rose locally above the 35 °C that the snakes started to bask slightly further from the hottest spot.

 Part 2