Thamnophis
HumboldtHerps.com
Thamnophis (3) I.D. Comparisons
Thamnophis (3) I.D. Comparisons
Information regarding scalation cross-referenced using:
1. Pages 665, 511, 669, and 674, The Audubon Society Fiel Guide to North American Reptiles and
Amphibians. c. 1979.
2. Pages 68-69, 210, 216, 220, and 226, Reptiles of the Northwest. c. 2002.
3. Pages 375, 378, 384, and 386, Western Reptiles and Amphibians (3rd ed.). c. 2003.
Web7. http://www.californiaherps.com/identification/snakesid/gartersnakeskey.html. (3 pages)
Web8. http://www.spiritone.com/~brucem/garter.htm ("The Plexus")
1. Pages 665, 511, 669, and 674, The Audubon Society Fiel Guide to North American Reptiles and
Amphibians. c. 1979.
2. Pages 68-69, 210, 216, 220, and 226, Reptiles of the Northwest. c. 2002.
3. Pages 375, 378, 384, and 386, Western Reptiles and Amphibians (3rd ed.). c. 2003.
Web7. http://www.californiaherps.com/identification/snakesid/gartersnakeskey.html. (3 pages)
Web8. http://www.spiritone.com/~brucem/garter.htm ("The Plexus")
Complete
Identifying species of garter snakes is often best done by determining differences in scalation. Distinctive sympatric
features usually exist in the upper and lower labial scales, internasal scales, chin shields, and mid-body scale rows.
Identifying the anal plate is not necessary, as it is single in all Thamnophis except the Mexican Garter Snake (T. eques).
_______________________________________________________________________________________________
Upper and Lower Labials
The Common Garter Snake (Thamnophis sirtalis)
10 lower labials
7 upper labial scales (occasionally 8, rarely 6 or 9)
The Northwestern Garter Snake (Thamnophis ordinoides)
7 labial scales (occasionally 8, rarely 6) 8-9 lower labials (rarely 7 or 10)
The Western Terrestrial Garter Snake (Thamnophis elegans)
8 labial scales (occasionally 7; 6th and 7th are 10 lower labials
enlarged, higher than wide)
The Pacific Coast Aquatic Garter Snake (Thamnophis atratus)
8 upper labials (6th and 7th less enlarged) usually 10 lower labials_____________________
Internasals
The Common Garter Snake - no specifics
The Northwestern Garter Snake - internasals shorter than prefontals
The Western Terrestrial Garter Snake - internasals usually wider than long, and not pointed in front
The Pacific Coast Aquatic Garter Snake - internasals usually longer than wide, and usually pointed in front
_______________________________________________________________________________________________
Chin Shields
The Common Garter Snake - rear longer than front
The Northwestern Garter Snake - no specifics
The Western Terrestrial Garter Snake - front equal rear in length
The Pacific Coast Aquatic garter Snake - rear longer than front
_______________________________________________________________________________________________
Scale Rows
Scale rows are usually counted at mid-body, because the numbers often differ at the neck and tail. We will not picture any
examples here as the only accurate way to do so would be to photograph a skin shed or a stretched skin. Since we do not
keep any garter snakes in captivity, shed skins of different species are difficult to attain; and we do not kill garter snakes!
The Common Garter Snake - 19 scale rows
The Northwestern Garter Snake - 17 (rarely 15 or 19)
The Western Terrestrial Garter Snake - 21 (rarely 19)
The Pacific Coast Aquatic Garter Snake - 19 or 21
_______________________________________________________________________________________________
Head Shape
A less accurate means of identifying our local garters is by head shape. Sympatric examples of the different species do
display some unique head characteristics. Please do not rely on these, for the plethora of hybrids and intergrades living in
this area may drive you insane! (Not to mention the many varieties that often exist within a single sub-species!)
The Common Garter Snake - no specifics (one could call this the typical or "common" garter head shape)
The Northwestern Garter Snake - over-all head size somewhat smaller (typical shape)
The Western Terrestrial Garter Snake - typical head shape, but often appears somewhat snub-nosed
The Pacific Coast Aquatic Garter Snake - elongated head and somewhat pointed
_______________________________________________________________________________________________
Good Luck !
As you become familiar with the described colors, patterns, and scalation of each species and sub-species you will also
need to ascertain any one group's geographical boundaries and preferred terrains [see Thamnophis (4)]. This may help
clarify some of the questions you might have about possible hybrids. For instance: Here in NC Humboldt County ( both
west of McKinleyville and east of Trinidad), we have found snakes that have all the features of a Northwestern Garter as
well as its range and preferred terrain; moving slightly further southeast, near the Mad River pump stations we found a few
specimens that appear to have the characteristics of both the Northwestern and the California Red-sided Garters; at first
we also considered that the Coast Garter could be involved (due to the similar red or orange dorso-lateral and ventral
flecking as well as its presence on the map), but after counting labial scales (unfortunately did not count scale rows) we
were more inclined to think otherwise; all had 7 upper labials (normal for both the Northwestern and the Common Garter);
using our guides as well as the "gartmodl" expert system GARTER key provided by Bruce G. Marcot's "The Plexus" (see
reference below) we deduced that at less than 10 labial scales (9!) we were indeed dealing with Northwestern traits;
however, some of the specimens had typically unflecked uniform light gray bellies, red heads, white lower labials, as well
as the clean lateral red spots on a black ground color - typical of the California Red-sided; we think this area is an
inter-specific hybrid zone and possibly the extent of the Northwestern's southern boundary; please refer to the SIGHTINGS
page(s) for more details.
We believe it is possible to make educated guesses as to the origins of some of these melting pots. Of course, the only
tried and true method these days, and with this genus in particular, is DNA forensics. Still, one should not take the fun out
of science by simply reducing everything to gene sequences, statistics and the likes. For the herper in the field there exists
the wondereful world of imagining the possibilities: "What will I find and what exactly will it look like? Northwestern X
Coast X California Red-sided X Mountain X Valley? Does the Western Aquatic ever join this medley? When 9 lower
labials cross with 10 lower labials, who wins? Is there a dominant tendency of one over the other? Or is everything
randomn?"
While mitochondria may help us ascertain the truth regarding origins, it does not show our eyes the beauty that is
revealed by the snake itself. On that note we say, "Happy herping! Hope you find a gem!"
features usually exist in the upper and lower labial scales, internasal scales, chin shields, and mid-body scale rows.
Identifying the anal plate is not necessary, as it is single in all Thamnophis except the Mexican Garter Snake (T. eques).
_______________________________________________________________________________________________
Upper and Lower Labials
The Common Garter Snake (Thamnophis sirtalis)
10 lower labials
7 upper labial scales (occasionally 8, rarely 6 or 9)
The Northwestern Garter Snake (Thamnophis ordinoides)
7 labial scales (occasionally 8, rarely 6) 8-9 lower labials (rarely 7 or 10)
The Western Terrestrial Garter Snake (Thamnophis elegans)
8 labial scales (occasionally 7; 6th and 7th are 10 lower labials
enlarged, higher than wide)
The Pacific Coast Aquatic Garter Snake (Thamnophis atratus)
8 upper labials (6th and 7th less enlarged) usually 10 lower labials_____________________
Internasals
The Common Garter Snake - no specifics
The Northwestern Garter Snake - internasals shorter than prefontals
The Western Terrestrial Garter Snake - internasals usually wider than long, and not pointed in front
The Pacific Coast Aquatic Garter Snake - internasals usually longer than wide, and usually pointed in front
_______________________________________________________________________________________________
Chin Shields
The Common Garter Snake - rear longer than front
The Northwestern Garter Snake - no specifics
The Western Terrestrial Garter Snake - front equal rear in length
The Pacific Coast Aquatic garter Snake - rear longer than front
_______________________________________________________________________________________________
Scale Rows
Scale rows are usually counted at mid-body, because the numbers often differ at the neck and tail. We will not picture any
examples here as the only accurate way to do so would be to photograph a skin shed or a stretched skin. Since we do not
keep any garter snakes in captivity, shed skins of different species are difficult to attain; and we do not kill garter snakes!
The Common Garter Snake - 19 scale rows
The Northwestern Garter Snake - 17 (rarely 15 or 19)
The Western Terrestrial Garter Snake - 21 (rarely 19)
The Pacific Coast Aquatic Garter Snake - 19 or 21
_______________________________________________________________________________________________
Head Shape
A less accurate means of identifying our local garters is by head shape. Sympatric examples of the different species do
display some unique head characteristics. Please do not rely on these, for the plethora of hybrids and intergrades living in
this area may drive you insane! (Not to mention the many varieties that often exist within a single sub-species!)
The Common Garter Snake - no specifics (one could call this the typical or "common" garter head shape)
The Northwestern Garter Snake - over-all head size somewhat smaller (typical shape)
The Western Terrestrial Garter Snake - typical head shape, but often appears somewhat snub-nosed
The Pacific Coast Aquatic Garter Snake - elongated head and somewhat pointed
_______________________________________________________________________________________________
Good Luck !
As you become familiar with the described colors, patterns, and scalation of each species and sub-species you will also
need to ascertain any one group's geographical boundaries and preferred terrains [see Thamnophis (4)]. This may help
clarify some of the questions you might have about possible hybrids. For instance: Here in NC Humboldt County ( both
west of McKinleyville and east of Trinidad), we have found snakes that have all the features of a Northwestern Garter as
well as its range and preferred terrain; moving slightly further southeast, near the Mad River pump stations we found a few
specimens that appear to have the characteristics of both the Northwestern and the California Red-sided Garters; at first
we also considered that the Coast Garter could be involved (due to the similar red or orange dorso-lateral and ventral
flecking as well as its presence on the map), but after counting labial scales (unfortunately did not count scale rows) we
were more inclined to think otherwise; all had 7 upper labials (normal for both the Northwestern and the Common Garter);
using our guides as well as the "gartmodl" expert system GARTER key provided by Bruce G. Marcot's "The Plexus" (see
reference below) we deduced that at less than 10 labial scales (9!) we were indeed dealing with Northwestern traits;
however, some of the specimens had typically unflecked uniform light gray bellies, red heads, white lower labials, as well
as the clean lateral red spots on a black ground color - typical of the California Red-sided; we think this area is an
inter-specific hybrid zone and possibly the extent of the Northwestern's southern boundary; please refer to the SIGHTINGS
page(s) for more details.
We believe it is possible to make educated guesses as to the origins of some of these melting pots. Of course, the only
tried and true method these days, and with this genus in particular, is DNA forensics. Still, one should not take the fun out
of science by simply reducing everything to gene sequences, statistics and the likes. For the herper in the field there exists
the wondereful world of imagining the possibilities: "What will I find and what exactly will it look like? Northwestern X
Coast X California Red-sided X Mountain X Valley? Does the Western Aquatic ever join this medley? When 9 lower
labials cross with 10 lower labials, who wins? Is there a dominant tendency of one over the other? Or is everything
randomn?"
While mitochondria may help us ascertain the truth regarding origins, it does not show our eyes the beauty that is
revealed by the snake itself. On that note we say, "Happy herping! Hope you find a gem!"
| Thamnophis Main Page |
| Thamnophis (2) I.D. Comparisons |
| Thamnophis (4) Ranges, Terrain, etc... |
| Scalation |
Front = Rear
Rear longer
pending
pending
