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Intergrades of Subspecies of
Aquatic Gartersnake -Thamnophis atratus

 






Aquatic Gartersnake California Range MapGray = North: Aquatic Gartersnakes formerly recognized as
the subspecies Thamnophis atratus aquaticus,
now recognized as an area of intergradation
between the three recognized subspecies.
South: T. a. atratus x T. a. zaxanthus intergrades.


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 the map for a topographical view








observation link

 

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.


Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade
  Adult, Marin County  
Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade
Adult, Marin County, left, with sympatric T. e. terrestris on right. Adult, Solano County
Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade Aquatic Gartersnake Intergrade
Adult, Marin County Adult, Marin County Adult from Marin County Headlands, just northwest of the Golden Gate Bridge
© Zach Lim
Aquatic Gartersnake Intergrade Santa Cruz Gartersnake  
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
 
western yellow-bellied racer western yellow-bellied racer

 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

     
Sympatric Gartersnakes
Gartersnakes Gartersnakes Valley Gartersnake
Two Marin County snakes:
Coast Gartersnake on top;
Aquatic Gartersnake on bottom.
Two Marin County snakes:
Aquatic Gartersnake on left;
Coast Gartersnake on bottom.
Three species found at the same Marin County location, including Thamnophis atratus, and Thamnophis elegans.
© Luke Talltree
     
Habitat
Aquatic Gartersnake Intergrade Habitat Aquatic Gartersnake Intergrade Habitat Aquatic Gartersnake Intergrade Habitat
Habitat, Marin County








Habitat, Solono County Habitat, Marin County

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