Breeding and care in captivity of the Santa Cruz Garter Snake (Part 3)

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

Steven Bol (Author…)


Adult female T.a.atratus (Captive bred; Taa 241) at an age of 2 years (65 cm total length).When the snakes are kept as described above it becomes obvious that the snakes are pregnant as early as April. The females are extremely voracious in this time of the year and they are sunning themselves all the time. Only in the last few weeks prior to parturition the appetite of the female starts to slow down although they usually never stop feeding completely.
Thamnophis atratus is oviparous just like all the other garter snake species. The young are born between end of June and end of July in my terrarium.
Table 1
shows an overview of the breeding results with 4 different females in the years 2000 – 2006.

In the wild average litter size is 7,8 and 8,4 according to Rossman, Ford & Siegel (1996).

Table 1

Table 1

In 2005 the 4 females gave birth to 56 young, of which 2 were dead. The average number of young in 2005 (fourteen) is above the average mentioned in literature, but my females are all fairly big (69 – 77,5 cm, see table 1) and well nourished. A 6 year old female of 84 cm gave birth of 26 (23 alive, 3 born dead)  young in July 2006.

In general larger, heavier and older females have larger litters then smaller females. Graph 4 shows the relation between the total length of the females and number of young per litter.

Graph 4

Graph 4

This graph 4 shows that length of female and litter size (including wax-eggs (the orange-coloured infertile eggs) and dead-born young) are strongly correlated.
The total length (measured right after birth) of the young of the 4 litters from 2005 (2 females gave birth at the same time in the same terrarium, so these young are treated as one litter) averaged 22,0 cm, 22,4 cm and 22,6 cm, which is larger the data from a female from Stanislaus Co., Ca. (18,7 – 20,9 cm): Rossman, Ford & Siegel (1996)The table in Rossman, Ford & Siegel (1996) mentioned a length which is very likely a mistake:  the snout-vent length for newborn males and females is stated as 99,1 and 100,4 mm .

Graph 3

Graph 3

The average snout-vent length of the 4 litters in 2005  mentioned above was 16,7 cm, 17,1 cm and 17,2 cm which is also longer then the data mentioned by  Rossman, Siegel & Ford (1996) in the species description: 12,6 to 16,6 cm. The smallest young in the 4 litters from 2005 measured 20,1 cm; the largest 27,3 cm (total length).

Graph 3 shows the correlation between the length of the female and the average length of the young.
These 2 parameters are not correlated as clearly as the length versus the number of young.
I think the temperature plays an important role in this (see the chapter “problems and diseases”).

Raising the young

After birth the young are separated from their parents and placed in smaller terrariums (52 x 35 x 30 cm or 32 x 27 x 30 cm) in groups of ideally not more then 10 snakes. Usually the young shed their skins directly after birth just like all other garter snakes, unlike the European Natricinae like the Viperine watersnake (Natrix maura) where this event takes place 7 – 10 days after birth.

In case the baby garter snakes have difficulties shedding their skins it is advised to place the snakes in a very moist container for a few hours. Then either try carefully to help the snakes with shedding their skin or place the snakes in their terrarium with sufficient rough surfaces likes rocks or pieces of wood so they can do it themselves. But usually this is not necessary and a sign of a lower fitness.

As far as temperature and decoration are concerned the terrarium for the young is identical to the one for the parents (see chapter “the terrarium”).

Normally I offer the babies food for the 1st time after a few days to a week. The diet consists of fish, just like the parents. Ideally the size of the fish is chosen so that the widest part of the fish is slightly wider then the head of the baby snakes (so they can eat it just barely at once).  Other wise I cut the fish in small pieces (including scales, intestine and bones). They are offered more food then they can eat within 12 hours, and normally the following day or morning the left over’s are removed.

Food is offered every 5 – 7 days.

In the last years raising the young has been without problems (see chapter “problems and diseases”).

Growth and age

Graph 1

Graph 1

Graph 1 shows the growth of some (offspring and wild caught) snakes born in 1999, 2000 en 2001.
The oldest female of known age is 7,5 years old (February 2007; female # 3) and measures 81 cm. The other females (female # 12 & 20) measured at the age of 5,5 years 84 cm and female # 12  measured  87 cm at the age of 6,5 years (January 2007).
The maximum length of Thamnophis atratus recorded  in the wild is 101,6 cm (Rossman, Ford & Siegel,1996). The largest female I have ever seen in California measured 78 cm .

Two males born in 2000 measured 71 and 68,2 cm at the age of 6,5 years. The largest males I have seen in California measured 78 cm.
The growth speed of males and females do not differ right after birth. Female 12 & 20 grew on average (in 3 years time) 6,7 cm per year  once they were 2,5 years old. Male 13 & 14 grew only  2,2 cm per year in the same period. Female 3 on the contrary grew more in line with the males (see graph 1)

Graph 2

Graph 2

Graph 2 shows  the growth of 2 litters born in 2005. These results show that growth speed can vary a lot. The litters of 2005 consisted of large and healthy young. This in combination with high quality food ( high quality Barbus spp. versus  smelt of sometimes questionable, dehydrated quality) and  a terrarium which is sufficiently warm can create an enormous growing speed.

It is never my goal to let baby snakes grow as fast as possible and I never feed the babies more then every 3 – 7 days. Despite of this the snakes of the 2005 litter grew fast: the  largest females measured appr. 60 cm and the largest males appr. 50 cm after one year (including a hibernation!). Graph 2 also shows that the growing speeds of the males and females do not differ much in the 1st year, although the growing speed of the females from litter 2 exceeded  both litters of males.

As I have described previously the oldest female (with known birth date) in my collection is currently over 8 years old (September 2007). A couple of Thamnophis atratus which must have been at least 3 years old in 2000 have celebrated their 10th anniversary this year in the summer of 2007 and both are still very healthy and vigorous and reproducing.

All three females of exactly known age in my collection gave birth to their 1st young at the age  of 3 years which means that they were sexually mature at the age of 2,5 years, directly after hibernation. At that time their length was 63, 64 and 64,7 cm.
When we compare this minimum length for sexual maturity with the females born in 2005 (graph 2) this may mean that some snakes can reach sexual maturity within 1,5 years. Those females could probably produce their 1st litters at the age of 2 years.

Rossman, Siegel & Ford (1996) recorded  as the smallest size for sexual maturity in females 38,6 cm snout-vent length (or 47 – 48 cm. total length).

The youngest age where I observed mating behaviour in a male was a little over 1,2 years (in the fall). The male measured at that moment 60,3 cm total length.

Problems and diseases.

Over the past 7 years of keeping Thamnophis atratus I have not had many problems.
Some things are worth mentioning though.

The first 2 years I kept the snakes in a large terrarium in which I tried to simulate the natural habitat. The snakes did not thrive very well, ate insufficient amounts of food and where rarely visible. Looking backwards I think that the terrarium was too cold in the spring and fall:  a combination of a large size (150 x 50 x 90 cm lxwxh), abundant ventilation and limited strength of the light bulbs. The poor circumstances may have increased the number of Flagellates, so I treated the snakes with FLAGYL (200 mg/ kg body mass, given oral twice with a ten day interval). After the snakes have moved too smaller and warmer terrariums limited appetite has not been an issue anymore and none of my snakes showed signs of mall nourishment.

The fact that my snake room is strongly influenced by outdoor temperatures makes simulating the temperatures as they are in spring in their natural habitat fairly easy: With strong light bulbs (since room temperatures are low early spring) the daytime temperatures rises sufficiently whereas the night temperatures drop down significantly. After the hibernation the behaviour of the snakes is observed closely: are they sunning themselves regularly, have they started mating and are they feeding well. If this was the case I usually did not measure the temperatures anymore in the past . And this created a potential problem!

The strong (60-75 watts) light bulbs, needed to heat up the terrarium early spring, were usually not replaced until they broke down or until I really noticed that temperatures got too high. I never measured the terrarium temperatures later in spring and summer so I do not have precise data. But over the years it slowly started to realise that I had a problem with temperatures rising too much inside the terrarium in the summer. Every now and then I did switch off the lights when high outside temperatures were expected, but there were several warm days were I forgot to do this. Or the temperatures rose unexpectedly, or I had not observed the weather forecast.

Table 1

Table 1

As I explained before the snakes moved to a smaller terrarium in 2002 after being in the large habitat terrarium for 2 years.

Table 1 shows that the breeding results of 2002, 2003 and 2004 were quit poor: 2002; 7 young born from 2 females, of which 5 were born dead (71 %), 2003; 22 young from 3 females of which 4 were born dead (18%) and in 2004; 44 young from 4 females of which 32 (72 %) were born dead. The results of 2004 were so obvious and disappointing that I realised something was wrong. I measured the temperatures at the coolest spot in the terrarium right after birth which was as high as 35 – 37 °C on some warmer days (room temperatures 31 °C).

A very stupid mistake! Over the years I had emphasised on higher temperatures in early spring to get the snakes started but forgot to slow down in late spring/early summer.

The high % of well developed but dead born young was not the only result I have observed due too high temperatures during the pregnancy of the females.

  • The young were relatively small (see table 1: 18,2 cm on average), a phenomena previously recorded in egg laying snakes with too high incubation temperatures.
  • A large number of young had a curly tail tip (similar to the tail of a pig).
  • A large number of snakes showed increased melanism.

The “pig-tails”, increased melanism and high number of still born young was also observed in Thamnophis sirtalis tetrataenia which was housed together with Thamnophis atratus.

Based on these facts I conclude that too high temperatures in the (in this case) last part of the pregnancy can lead to a high percentage of dead born young, smaller young, increased melanism and the occurrence of a “pig tail”.
As far as I know this has not been described previously in literature. 

I do realise that other factors can play a result since I have not done real trials to confirm my suspicions under controlled circumstances.
In order to try to prevent this from happening I placed a thermostat in my snake room early spring 2005 which automatically shuts off all light bulbs once the temperature reaches a certain maximum temperature. As a threshold I usually use 24 – 26 °C (depending on time of the year. In the summer I use bulbs with lower amount of Watts which lowers the difference between temperature inside and outside the terrarium)

Looking at the breeding results (table 1) the effects of a better temperature management seem obvious: in 2005; 56 young from 4 females of which 2 were born dead (3,5 %) and no “wax eggs”; in 2006; 57 young of which 3 were born dead (5,2 %) and no “wax-eggs”. The average length was 22,7 cm and not a single baby with a “pig tail”.

Concluding remarks

Thamnophis atratus is a very attractive species. They are diurnal and because of that they are easily visible in the terrarium every day. They have no problems feeding and accept a wide range of food, are relatively quiet and relatively easy to breed. Because of these facts it is a very nice garter snake species to keep and raise in captivity.  They are both interesting for the more experienced  hobbyist as for a new starter.

With this article I hope to make this unknown species more well known. When the suggestions and recommendations described in this article are followed I expect that everybody who acquires healthy specimens will enjoy this species a lot and will be able to reproduce them successfully.


Breeding and care in captivity of the Santa Cruz Gartersnake, Thamnophis atratus atratus (Kennicott, 1860).
In this article an unknown gartersnake is introduced: Thamnophis atratus atratus.
After a short description of the animals and their natural habitat the author discusses the husbandry of this species.
The requirements of the terrarium are described extensively.
The author considers hibernation essential for keeping this species true to nature and for systematically breeding these animals.
Also newly-born animals hibernate at an age of five months.
The active season following the hibernation and the reproduction is described and some data accumulated in the last six years are analyzed.
The data on growth of several individuals are given, as is the variation throughout the years.
Remarks are made concerning age and length when reaching sexual maturity.
Finally some notes are given to problems and diseases with this species.
An, until now in the literature never described, effect of keeping the animals too warm during pregnancy (percentage still-born, length of the juveniles, “pig-tails” and colour) is described.

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., 2004. Hibernating Garter Snakes: A must or an option. The garter snake 9 (2): 3-11
Rossman, D.A., N.B. Ford & R.A. Siegel, 1996. The Garter Snakes. Evolution and ecology. University of Oklahoma Press, Norman
Zwart, P., 1982. Thiaminase (antivitamine B1) in de slangenvoeding. Lacerta 40:96-97