Breeding and care in captivity of the Santa Cruz Garter Snake (Part 2)

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

Steven Bol (Author…)


Biotope of T.a.atratus and T.e.terrestis in San Mateo County, Californië. Sun shines in July from 7:30 hour on the banks where the snakes take a sunbath.The Californian Coast is climatically strongly influenced by the Pacific Ocean. Due to the southern latitude de radiation of the sun is very intense, but during wintertime their will be long periods with rainy/cloudy/foggy weather during which it will be too cold for the Santa Cruz Garter Snakes to remain active. In literature is written that snakes can be seen on mild winter days, but that does not exclude a hibernation period.
Especially the coastal strip of California is foggy and cloudy.

Middle March 2003 I visited the natural habitat of this species in California: The weather was rainy and foggy and temperatures were around the 10°C. Between noon and 2 PM when the sun tried to peak through the clouds limited activity of Thamnophis atratus could be noted. Two snakes were sunning themselves. It was clearly mating season for the amphibians (Tree frogs, Hyla spp. and Taricha torosa, The Californian Newt) and the first willow trees just started to turn green. These observations so “late” in spring gave me the impression that this species does hibernate during wintertime.
I hibernate my snakes for approximately 3,5 month (15 weeks) starting early November and ending end of February.  I do this for the following reasons:  keeping the snakes in a way that closely resembles the natural situation and breeding them according a planned method. For more details about the material and methods of the hibernation please read Bol (2004).

Minimal 1,5 – 2 weeks before the start of the hibernation (early November) the snakes are offered food for the last time  but  I keep the terrarium well heated  so that it no undigested food remnants stay behind in the intestine channel.
Then I switch off the lamps/heating. The animals remain then in the unheated snakes room by temperatures that in this time roughly fluctuate between 8 – 12°C. 

During periods with severe frost the temperature can get as low as  2 to 4°C, and on soft sunny days the temperature may occasionally rise up to 14 to 16°C (only for a few hour in the afternoon). After a short period in the unheated terrarium (at most four weeks, mostly shorter), I place the snakes in a hibernation box. I use for this metal (old cake drum) or plastic containers (relative small: content approximately 3 – 5 liter) with limited ventilation capacity created by some  holes in the lid.  This is of essential, since garter snakes are prone to dehydration during the hibernation, especially in the fridge. The containers are  filled for two third with a mixture of sawdust and damp leaf (normally from the garden, no need for disinfection ), and I make sure the substrate is slightly humid by sprinkling water over it.  As long as the insides of the lid contains some water droplets due to condensation I consider the substrate to be damp enough, otherwise I sprinkle some extra water.

In this way the snakes hibernate, without water tanks, in the containers in the unheated snake room.
I check approximately once per month to see if the snakes are OK. Often the animals lie on the substrate or they have crawled away in the substrate. After opening the box the snakes react by tasting the air with their tongues or possibly slowly crawling around.

My experience is that as long as the substrate is damp enough the snakes survive this hibernation period of 3.5 month easily, hardly lose any weight (maximum 3 – 5% weights loss, average in 2006 was 0,8%) and they still are in perfect shape after the hibernation period. I have never seen any problems with a substrate which was too damp, aside from a small spot on the skin (blister) that was slightly inflamed. But after the snakes have shed their skins for the first times these blisters normally vanish. Over the past six year that I have hibernated this species in this way not a single one died.

Also young snakes, which usually are a few months old in November, hibernate in the same way as the adult animals (in the wild these young snakes also do not receive a special treatment). The only difference is that the duration is shorter: a minimum of eight, at most eleven weeks.


The snakes are placed back after the hibernation, mostly around end of February, in the heated terrarium. A transitions period is not created and from the first day onwards I try to create a warm spot locally of 30 – 35°C. Usually the snakes react by sunning themselves almost the whole day directly underneath the lamp.

In the nature these transitions also do not occur gradually. ROSSMAN, FORD & SIEGEL (1996) give an excellent example of the daily fluctuations in the body temperature of a Thamnophis elegans in California in April. During a cold night the snake has a body temperature of 8°C (from  6 o’clock in the evening until 9 o’clock in the morning), after which it rises rapidly, under the influence of the powerful sun, to a maximum of 25°C around 12 o’clock at noon. Around 3 o’clock in the afternoon the body temperature is still 20°C after which it drops gradually to 8°C. Mating behavior starts almost immediately after ending the hibernation (when the terrarium warm is enough) and during the first weeks the males hardly leave the side of the female.

Mating behavior can sometimes be observed for days or weeks in a row (until end of March).  The male lies on top of the female and attempts to curl his tail underneath and around the tail of the female.  Heavy shocks run through the body of the male. I do not separate the sexes during the year; males and females live year-round in the same cage. Keeping the snakes separate in order to stimulate mating behavior is absolutely not necessary in my opinion. The only disadvantage of keeping the snakes together is that it diminishes the chance of witnessing a real mating so you are never 100 % sure whether the snakes have mated successfully.  I have observed successful mating of this species within 10 – 21 days after the hibernation (long before the first shedding).

Mating behavior in fall and after giving birth is very common. This is in contradiction with  Rossman, Ford & Siegel (1996) who mention a case of  fall mating as an exceptional observation. Observing this in the wild may be exceptional, and this is an example how keeping snakes in captivity can contribute to the knowledge about the biology of a species.

Within 1-2 weeks after hibernation the Santa Cruz Garter Snake can start to feed in captivity. When the terrarium is (too) cool the snakes may refuse to eat for several weeks.  The first meals may be moderate. But soon the snakes (especially the females which are pregnant) become very hungry. Early to middle April the females are noticeably pregnant, and the skin between the scales remains clearly visible even several days after feeding.

In captivity the Santa Cruz Garter Snake shed it’s skin  relatively late: the first shedding usually occurs 7,5-11 weeks after the hibernation has ended. This is mostly around end of April-beginning of May, much later then some other species of Garter Snakes like Thamnophis sirtalis spp. This is why I consider a method which is often used to stimulate mating unsuitable: putting the snakes together after the snakes have shed their skins for the 1st time. Normally the snakes are noticeably pregnant around this time.


The snakes are offered a diet of almost exclusively fish. Smelt, Barbus spp. and other (mostly freshwater) fish species. Only in 2004 I offered quit a lot of mice (dead, thawed), because the limited availability of smelt from Holland. But I the snakes received the mice always together with fish. Thamnophis atratus accepts mice quit easily specially when scented with fish.

The snakes are fed every five to seven days and they can eat a s much as they want. The (thawed) fish are offered on a small plate in the terrarium mostly in the evening. I remove the fish the following day. Because the Santa Cruz Garter Snakes (especially pregnant females early spring time) react quit hungry and aggressively to fish it is wise to remain present while they are eating to prevent that 2 snakes start eating the same fish. The much smaller male (including fish) could easily end up in the stomach of the much bigger female. Especially when you keep a group of 10 -20 young snakes in the same cage this can happen easily.

To prevent a deficiency of Thiamine (Vitamin B1; see Zwart 1982) I add several droplets of vitamin B1 every time if feed them. Multivitamins (mostly Nekton Rep) I add only once every 1 – 2 month.
Since the snakes are fed with whole fish including bones, intestines and scales adding calcium is absolutely unnecessary and I have never done it.

Thamnophis atratus is a heavily built and large Garter Snake which can get fat quit easily. Do not feed them too often, especially when they receive a lot of mice.

Life fish are hardly given, but that is more because of practical constraints. Sometimes I give the young snakes life fish to stimulate them to start feeding. They respond very well to it.

In the wild the diet consists beside fish of amphibians like frogs, toads and newts (Rossman, Ford & Siegel, 1996). But I never give them amphibians (sine they are protected in Holland). In literature worms and slugs are not mentioned as part of their diet. In their natural habitat in early spring worms are abundant (personal observation) and I do expect they will eat worms.

Part 3