A Guide to the Amphibians
and Reptiles of California
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Intergrades of Subspecies of
Aquatic Gartersnake -Thamnophis atratus
Gray: Range of Aquatic Gartersnakes formerly recognized asthe subspecies Thamnophis atratus aquaticus,
now recognized as an area of intergradation
between the three recognized subspecies.
Range of Thamnophis atratus subspecies in California:
Red: Thamnophis atratus atratus - Santa Cruz Gartersnake
Orange: Thamnophis atratus hydrophilus - Oregon Gartersnake
Light Blue: Thamnophis atratus zaxanthus -
Diablo Range Gartersnake
Click on the map for a topographical view
Map with California County Names
| North of the San Francisco Bay, there is a very large range of intergradation between three subspecies of Thamnophis atratus: Thamnophis atratus atratus - Santa Cruz Gartersnake Thamnophis atratus hydrophilus - Oregon Gartersnake Thamnophis atratus zaxanthus - Diablo Range Gartersnake The snakes in this area were formerly classified as Thamnophis atratus aquaticus (or Thamnophis couchii aquaticus.) This subspecies is no longer recognized. South of the SF Bay there is a small area of intergradation between Thamnophis atratus atratus - Santa Cruz Gartersnake and Thamnophis atratus zaxanthus - Diablo Range Gartersnake. |
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| Adult, Marin County | ||
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| Adult, Marin County, left, with sympatric T. e. terrestris on right. | Adult, Solano County | |
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| Adult, Marin County | Adult, Marin County | Adult from Marin County Headlands, just northwest of the Golden Gate Bridge © Zach Lim |
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| This aquatic gartersnake found in Marin County lacks the distinct pattern and the lower lateral stripe typically found on the Oregon Gartersnake and on the northern intergrades, which gives it the appearance of a Santa Cruz Gartersnake. © Andre Giraldi | Possible T. a. atratus x T. a. zaxanthus intergrade adult, Santa Clara County © Jared Heald |
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An adult Western Yellow-bellied Racer was observed trying to swallow an Aquatic Gartersnake on a lawn in Sonoma County, but the observers apparently spooked the racer, which dropped the gartersnake then climbed a rose bush. © Don KcKee |
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| Sympatric Gartersnakes | ||
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| Two Marin County snakes: Coast Gartersnake on top; Aquatic Gartersnake on bottom. |
Two Marin County snakes: Aquatic Gartersnake on left; Coast Gartersnake on right. |
Three species found at the same Marin County location, including Thamnophis atratus, and Thamnophis elegans. © Luke Talltree |
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| Two species of gartersnakes found at the same Marin County location: Left - Thamnophis atratus Right - Thamnophis elegans |
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| Habitat | ||
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| Habitat, Marin County |
Habitat, Solono County | Habitat, Marin County |
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