Hibernation, diet, habitats, dimorphism and mating

Garter snakes are colubrids, (member of Colubridae, a widespread and non-venomous group of snakes) and are found throughout North America. They belong to the genus Thamnophis, and there are 28 different species of garter snakes, and even more sub-species. The common garter snake is Thamnophis sirtaris - it is found in as north as Alaska and as south as New Mexico. Usually, garter snakes reach a length of 2 to 5 feet. They have a brown «background color» and longitudinal stripes in different color: red, yellow, blue, orange, or white. They also have rows of blotches in between the stripes. The name Garter snake comes from the fact that the stripes resembles a garter.

Garter snakes are diurnal and very active during day time. That make them particular interesting as pets, as they can be watched most times during the day. Also, they are very alert and curious.

The key to finding garter snakes is the water source. If you are looking for Garter snakes the best thing is to look around ponds, turn rocks etc. to see if there are any snakes beneath them.

In the wild, garter snakes can carry parasites and worms, which they can manage that in the wild where they have lot of sunlight, and perhaps a more varied diet.

In captivity they are more subjectible to stress and most wild caught garter snakes are difficult to keep.

                                                                        

The frog is caught at 1:08



It starts biting after 30 seconds



Garter snakes emerging from den

Diet

Depending on geographic location, prey availability and sub-species in question, the diet of garter snakes is quite varied. However, some have pointed out that they do prefer frogs (anurans, tail-less amphibians) to such an extent that it is notable.

They also eat eathworms, and fish. The great versatility in prey choice explains why Garter snakes have been so successful in occupying many different habitats and why they are found all over ”the United States.

The chart below depicts data from an article by Tuttle & Gregory (2009)1 where the stomach content of 548 garter snakes was investigated. The investigation took place in Alberta, Northern Canada, in a period from 1995-2006, and the only snake investigated was Thamnophis radix (Plains Garter snake). Although garter snakes in southern states may have a more varied diet, frogs are very popular among garter snakes, especially in Canada, where there are many frogs. In captivity, Garter snakes are mostly fed with rodents, which works out fine. For garter snakes hairless mice are preferred.

A chart with the composition of prey in a Canadian Garter snake population

Fig 1. A population in Canada with a very uniform diet.

However, it is widely accepted that Garter snakes are generalists (Drummond, 1983)2. In the study by Drummond it was shown that generalist species such as T. sirtalis had a diet consisting of more than 5% earthworms, mammals, salamanders, anurans, tadpoles, fish, leeches, and birds while T. elegans, also a generalist, had a diet of more than 5% slugs, mammals, anurans, tadpoles, fish, leeches, and earthworms (ibid). A specialist aquatic Garter snake, such as T. melanogaster ate mainly fish, tadpoles, and leeches, another study showed.

Toads are a favorite of the Garter snake
Although the toad is much bigger than the garter snake, the garter snake has no problem in eating a toad much larger than itself.

Due to dangers involved in subduing larger mammals, there were not many adult rodents among the prey items in both studies. In contrast, some garter snakes seem not to be affected by some types of toxins at all. Three different species of garter snakes (see short facts column) are immune to TTX, a toxin from newts (Feldman et al., 2009) and in California, T. hammondii has no problem eating an introduced toxic frog (Foster & Mullin, 2008)4.

Hibernation

In some places, at high northern altitudes, Garter snakes doesn't eat in a prolonged period from October to May. Further south, e.g. in Florida, they doesn' hibernate at all. During hibernation Garter snakes haven't access to food, and in these periods the absorbed relatively more water in those periods5. In a period before hibernation they tend to spend most of their time near the den, and are in the den whenever it is cloudy weather or particularly cold.

For some unknown reason, Garter snakes older and younger than on year doesn't hibernate together. It's a mystery why not. This phenomenon is also referred to as the lost year.

Up to 12,000 to 15,000 Garter snake may hibernate together (se video). In climates where temperatures might reach -40oC (-40oF) it is apparantly vital that many individuals hibernate together.

Habitat

Garter snakes are semi-aquatic, and prefers habitats that are close to water. Garter snakes can be found as far north as Alaska which makes it one of the most northermost species in the world. In more habitable areas, the Garter snake will just live where ever ih has water and prey nearby.

Sexual dimorphism

In garter snakes females are larger than males. There may be several reasons for this. Theories related to sexual dimorphism explain the phenomenon as being due to either i) differential utilisation of niches between males and females and or ii) the advantage of having larger females with better reproductive capabilities (Krause & Burghardt, 2006)6.

Mating

There are far more males than female Garter snakes. Therefore, males will try and mate any female any time. After hibernation males will form a so called mating ball around a female - all of the trying to be the one to mate the female. The average litter is 15-20, but it varies a lot from numbers as low as 2 to as much as 40 baby Garter snakes in a litter. They are born live.

Resources

General Exotics
Thamnophis - community

References

1 Tuttle, K.N. & Gregory, P.T. Food Habits of the Plains Garter Snake (Thamnophis radix) at the Northern Limit of Its Range Journal of Herpetology 43(1) pp. 63-73, (2009).
2 Drummond, H. Aquatic Foraging in Garter Snakes: A Comparison of Specialists and Generalists Behaviour, 86(1/2), pp. 1-30 (1983)
3 Feldman C.R., Brodie E.D., Pfrender M.E.The evolutionary origins of beneficial alleles during the repeated adaptation of garter snakes to deadly prey Proc. of the National academy of sciences of the United States of America 106(32) pp. 13415-13420, (2009).
4 Foster C.D. & Mullin S.J. Speed and endurance of Thamnophis hammondii are not affected by consuming the toxic frog Xenopus laevisSOUTHWESTERN NATURALIST 53(3) pp. 370-373 (2008).
5 Aleksiuk, M. & Stewart, K. Seasonal Changes in the Body Composition of the Garter Snake (Thamnophis Sirtalis Parieltalis) at Northern Lattitudes Ecology, 52(3) pp. 485-490 (1971)
6 Krause M.A. & Burghardt, G.M. Sexual dimorphism of body and relative head sizes in neonatal common garter snakes Journal of Zoology 272 pp. 156-164 (2007)

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