Author: Jerry G. Walls Copyright: TFH Publications
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North American
garter snakes and ribbon snakes, genus Thamnophis, are widely kept in the
U.S. and Europe, but some species are much more available than others. Of the 30
species recognized as valid in the last review of the group by Rossman, Ford
& Seigel (1996, The Garter Snakes. Evolution and Ecology, Univ. Okla.
Press, Norman, OK), just over half (16) are found in the U.S., the other 14
being restricted to Mexico and Central America.
In the U.S. there are
concentrations of species in the Pacific Coast states, the Southwest, and the
eastern part of the country. Species from all these areas enter the pet shops
and frequently are found on dealer lists. In this article I'll restrict our
discussion to just four rather unusual species that are found in the U.S. only
from central Texas to the California border, at the northern edge of their
mostly Mexican ranges. Though a few other species of garter snakes enter this
area from the north (T. sirtalis, T. proximus, T. radix, most commonly),
the four species that catch our attention here are all distinctive enough to not
be easily confused with the more mundane
species.
Recognition Three of these southwestern specialty
garters are similar enough to be easily confused at first glance, while the
fourth is so different from any other snake in the U.S. that it is not likely
even to be recognized as a garter snake. Let's take the true oddball
first.
Thamnophis rufipunctatus, the Narrow-headed Garter Snake,
looks like a water snake, genus Nerodia, in lacking stripes and having a
strong belly pattern. This highly aquatic snake has a narrow head with a rather
long snout, two scales (preoculars) directly in front of the eye (one in the
other garter snakes covered here), and lacks all traces of middorsal and lateral
stripes. Instead, it is a pale to dark brown above with small rounded reddish
brown to dark brown spots in three to six rows across the back. The spots may be
distinct or connected into irregular brownish cross-bands.
On the belly
the whitish ventral scales have brown wedge-like smudges at their front edges on
each side and often either a brown bar or spots on each ventral. The similarity
to water snakes is increased by the presence in some populations of a divided
anal scale in up to 10 percent of specimens. (Thamnophis has a single or
undivided anal scale, while Nerodia has a split or divided anal scale;
there are few other differences between the garter and water snakes.) Adults
generally are about 16 to 20 inches long, with exceptional giants over 44 inches
in length. The very narrow head gives the snake a distinctive appearance,
especially when combined with the multiple rows of brown spots over the back,
and it is not likely to be confused with any other garter—or water—snake in the
country.
Also fairly distinctive is the Checkered Garter Snake,
Thamnophis marcianus, recognizable by its overall pale olive to tan
coloration with extremely narrow pale stripes. The middorsal stripe is yellow to
cream, while the lateral stripes are whitish to pale yellow and very narrow,
seldom more than one scale wide; the lateral stripes are on the second scale row
to the back of the body, the third row on the front part. Between the stripes on
each side are two rows of squarish black spots that alternate in a distinctly
checkered pattern and project into the pale stripes, given them obviously wavy
edges.
The top of the head is a bright grayish olive, with a pair of very
large deep black blotches on the neck, separated by the middorsal stripe. The
grayish olive from the top of the head extends down to cover the lips behind the
eye, isolating a narrow white to bright yellow crescent over the angle of the
jaws, an easily seen character. Adults usually are 18 to 24 inches long, with
outstanding giants of nearly 44 inches recorded.
Similar enough to be
easily confused and with overlapping ranges are the Black-necked Garter Snake,
Thamnophis cyrtopsis, and the Mexican Garter Snake, T. eques.
Technically the two species are easily distinguished by counting the number of
rows of dorsal scales at midbody: there are 21 or 23 rows in T. eques (a
count also found in T. marcianus) but only 19 in T. cyrtopsis.
Both are similar in general appearance, being brown to blackish with bright
stripes and usually weakly defined large dark spots on the sides between the
stripes. However, in T. cyrtopsis the lateral stripe is on scale rows two
and three, while it is on rows three and four in T. eques.
Both
have a large squarish black blotch behind the head on each side, and in T.
eques there may be a fairly distinct pale crescent in front of each blotch
over the angle of the jaws. In the Black-necked Garter Snake the middorsal
stripe often is bright orange at the back of the head, becoming yellow and then
whitish more posteriorly. Black-necks often have moderately distinct black spots
on the sides, especially on the neck, but these do not remain large and distinct
on the back half of the body as in the Checkered Garter Snake; the spots seldom
are strongly distinct the Mexican Garter Snake. Both species are 16 to 28 inches
long as adults, rarely reaching much over 40 inches.
Ranges and
Availability All four of these snakes occur in Mexico, with two (T.
cyrtopsis and T. marcianus) occurring well into Central America. None
ranges east of central Texas or north of roughly a line from southern Utah to
southern Kansas. Two of the species, T. marcianus and T.
cyrtopsis, have broad ranges in the U.S. and are relatively commonly
collected, while the other two species have small ranges even in Mexico and are
rare and spottily distributed in the U.S., being found only in Arizona and New
Mexico.
Narrow-headed Garter Snakes seem to occur in two separated areas,
with most of the range in northern central Mexico and a small remnant group of
populations in a band from central Arizona barely into western New Mexico. In
the U.S. it seldom is common and is protected by both the states where it
occurs. It should not be available legally without permits.
Though the
Mexican Garter Snake is found over much of central Mexico from the Arizona line
to Oaxaca in the south, it occurs in the U.S. only in southeastern Arizona (with
a seemingly isolated group of populations in the central part of the state) and
a few localities in southwestern New Mexico near the Arizona line. It seldom is
found in large numbers (and may be virtually extinct in New Mexico) and is
protected in the U.S. Three rather questionable subspecies are recognized, with
T. eques megalops occurring in the U.S.
Thamnophis
cyrtopsis is found in the lowlands of much of Mexico south into Guatemala
and then north into southern Utah and Colorado. In the U.S. it ranges from
western Arizona into western Texas plus the plateau region of central Texas. Two
subspecies are found in the U.S. (with a third restricted to Mexico and Central
America). T. c. cyrtopsis occurs from Arizona to western Texas, while
T. c. ocellatus is restricted to central Texas.
The two subspecies
are similar in all respects, but in ocellatus the pairs of black spots
are fused into single larger spots on the neck and take on a weakly triangular
form with the point extending into the lateral stripe; ocellatus often
also has short white stripes prominently developed in the dark area between
spots on the sides, these weak or absent in the often paler and less strongly
spotted T. c. cyrtopsis.
Checkered Garter Snakes certainly are the
most easily found southwestern garter snakes, with a nearly uniform range in the
U.S. from central Texas to southern Kansas and west across mostly southern New
Mexico and Arizona to the California border. It is found over the western
two-thirds of Texas and also widely over northeastern Mexico. Though the species
ranges south to Costa Rica, it is absent from virtually all of southern Mexico
and is known as only small, isolated populations representing two unique
subspecies from the Yucatan area into Central America. The subspecies in the
U.S. is T. marcianus marcianus.
Habits In many respects
the most "normal" garter snake discussed here is the Checkered Garter Snake,
which is found from lowlands well into the mountains. It is not especially
aquatic, though it may be most common near ponds, lakes, cattle tanks, and
streams; it has taken advantage of irrigation ditches and other manmade
structures to expand its range into areas that formerly were too dry for it. It
is a great prowler, often crossing roads at night during hot weather and being
found hunting for frogs, lizards, and other prey in the morning and evening
during cooler weather.
Black-necked and Mexican Garter Snakes are much
more aquatic, being almost restricted in the U.S. to the vicinity of mountain
streams and ponds, often at high altitudes. Black-necks often forage in moving
streams and can be found in the water more often than on land, while Mexican
Garters seem to prefer moist, grassy areas with lots of cover at the edges of
stock ponds. Both feed heavily on tadpoles and small frogs likely to be found in
their habitats, with T. eques also taking a variety of small fishes.
There is good evidence that both species, like other garter snakes, will take a
variety of prey, including lizards and earthworms, if their preferred prey is
sparse.
In keeping with its water-snake-like form and color pattern, the
Narrow-headed Garter Snake is found mostly in moving streams and rivers that
have large rocks and riffle areas. Though it basks on the shore and on
overhanging vegetation, it is more aquatic than the other garter snakes of the
area. It lives and hunts in the gaps between piles of rocks (from head-size to
boulders), using the tail to help anchor it in rapid water. The prey consist
mostly of small native minnows and other southwestern fishes, but it also will
take young sunfish and trout, both introduced into its range. Obviously its
habitat preferences are hard to match in the U.S., where the tendency is to
channelize anything that moves and replace rocks with shallow sandy or muddy
areas.
Keeping Hobbyists and scientists have had fair to
excellent luck keeping all but the Narrow-headed Garter Snake in the terrarium.
As with most other garters, the trick seems to be to ignore much of what is
known of their natural history and force the snakes to accept seemingly
unnatural tanks and diets. If the more aquatic garter snakes are kept in water,
they rapidly succumb to blister disease caused by Aeromonas and other
bacteria.
Instead, they are kept in simple, virtually dry surroundings.
Single specimens (beware of cannibalism, especially if specimens of two widely
different sizes are kept together) can be kept in a 10-gallon terrarium with a
layer of shredded aspen fibers or even on paper towels or indoor-outdoor
carpeting. A hidebox of the appropriate size is placed in the terrarium along
with a water bowl just large enough to allow the snake to submerge or to hunt
for tadpoles.
A low-wattage bulb (25W) over one corner of the tank will
provide basking light and warmth, and there should be a basking surface (rocks,
branches, etc.) as well. Ultraviolet light does not seem to be necessary, as
these snakes are not strong baskers and often are active (during hot weather)
mostly at night. Several keepers have reported that these garter snakes display
a better appetite and increased survival rate if given an undertank heater as
well as a basking light. All accept a wide range of temperatures, from 72° to
90°F (preferably 80° to 86°F), for normal activity.
Though the natural
diet of these garter snakes consists mostly of aquatic and semiaquatic lower
vertebrates, including tadpoles, small frogs of all types, salamander larvae,
and occasionally small fishes, in captivity they usually are trained to accept
mice as the staple diet. Young specimens may have to be started on tadpoles or
frogs, but they then should be given pinkie mice or pinkie parts until they
learn to accept this less smelly, easier to maintain food. Checkered Garter
Snakes have been known to take mice in nature, and even wild-caught adults
rapidly begin to take mice; this helps the species maintain its reputation as
one of the best garter snakes in captivity. Little has been reported on whether
these garter snakes need vitamin and mineral supplementation, but once adapted
to mice they should be receiving a calcium-rich diet. Feed a mouse diet once a
week, tadpoles and frogs twice a week.
Keeping the Narrow-headed Garter
Snake is a challenge because of the legal problems in obtaining specimens, the
rarity of the species in the U.S., and the highly aquatic nature of the species.
However, some specimens have successfully been kept much like the other garter
snakes in a nearly dry terrarium on a mouse diet. This may be exceptional,
though, as there are several reports of specimens that did well only when kept
in water (the species seems to be very resistant to blister disease) and fed on
fish. It seems to need lower temperatures than the less aquatic garter snakes to
become fully active, being comfortable at 80° to 84°F. Because of the many
problems with this species, it cannot be recommended for amateur
collections.
Breeding As far as known, all four of these snakes
are truly viviparous snakes, a placenta-like membrane forming between the
developing young and the mother's circulatory system, with some exchange of
nutritives and waste gases, much as in mammals. Additionally, garter snakes are
known to store sperm after mating, actual fertilization of the eggs occurring
days to months later. This makes it difficult to estimate gestation periods,
though four months seems to be a common guess.
Mating takes place after a
period of hibernation, which in the terrarium is simulated by dropping the
temperature to 50 to 60F for six to eight weeks while reducing or eliminating
feeding. Males and females usually are kept separately and then introduced to
each other in the spring, with natural mating most common from March to May.
There are many reports of these garter snakes mating in the late summer or
autumn before hibernation, actual fertilization being delayed (apparently) until
the following spring.
Gravid females soon become recognizable by their
heavier bodies and more persistent basking, as well as often a reduced appetite
until just before delivery of a brood of commonly 6 to 30 young that are 5 to 8
inches long and much like the parents except with brighter
coloration.
Garter snakes grow rapidly, usually tripling their length in
their first year if there is sufficient food and warmth. Sexual maturity
typically is reached by their second or at least third year of age, and (though
only the Checkered Garter Snake is truly well-known) they probably can live to
between six and ten years of age.
Checkers-the Best Garter
Snakes Unfortunately, few Black-necked, Mexican, or Narrow-headed Garter
Snakes have survived more than two or three years in captivity. Checkered Garter
Snakes, on the other hand, are excellent, long-lived terrarium pets, being
widely available as captive-bred specimens. Even wild-caught adults, once
rehydrated and vetted to reduce their parasite load, adapt well to many keeping
conditions and will take almost any food offered. Remember their susceptibility
to blister disease, however, and never keep them too wet.
Some lines have
been captive-bred for several generations by now and will breed with minimal
hibernation. They also are gentle snakes that learn to be handled in just a few
days, seldom biting or expelling their vent contents and anal glands as is
common in other garter snakes.
Almost all specimens, captive-bred or
wild-caught, are attractive, sometimes colorful, and the snakes remain a good
size for a small, simple terrarium. Additionally, Checkered Garter Snakes now
are being selectively bred for brighter contrast in coloration, and albinos are
common and affordable. Good size, good color, easy to keep and feed-what more
could a hobbyists desire?
Jerry G. Walls is a former
editor of Reptile Hobbyist. He is the author of TFH's Jewels of the
Rainforest, among many other books and magazine articles. He lives in
Trenton, NJ, with his wife, Maleta.