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Aquatic Gartersnake (Intergrade)

Thamnophis atratus atratus X zaxanthus X hydrophilus


This subspecies has been determined to be an intergradation of these subspecies of aquatic Gartersnakes in a range of the north bay area:
Thamnophis atratus atratus - Santa Cruz Gartersnake
Thamnophis atratus hydrophilus - Oregon Gartersnake
Thamnophis atratus zaxanthus - Diablo Range Gartersnake
This resembles mostly the Diablo Range subspecies with the center being more light colored instead of orange. And it has the wide light color underneath that comes up the sides more then the others. This snake has no visible red. This was a medium to large Garter.
It was first believed that Gartersnakes were nonvenomous. Turns out they found that they do have venom but in low levels that is only toxic to it's prey and not to humans or large animals.


Spotted at a golf course. It had come out of the landscaping.


I spotted this snake just after it captured a Vole. I heard the squeaking as both rolled down hill. The jaws of the snake were still separating and trying to hold onto the vole. The location lists Intergrade species all being aquatics with a diet mainly on amphibians and fish. Drought may have changed the diet on these aquatic species.

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Jellis 7 years ago

Yes Hema. Any oil spill is bad news for birds and more.

Jellis 7 years ago

Thank you Mark

Mark Ridgway
Mark Ridgway 7 years ago

Great spotting Jellis.

Hema 7 years ago

what a bad timing for the Galveston oil spill. t is so heartbreaking!!

Jellis 7 years ago

yes but the levels are too low to effect humans. It only effects it's prey.

Hema 7 years ago

that is sad indeed. These are venomous?

Jellis 7 years ago

Thank you Hema.
And the sad part is it may not have eaten it. These are aquatic Garters. Their diet is frogs, newts and fish. Because of the drought it's diet changes,but their jaws may not be able to open wide enough for something this big. I didn't stick around to see

Hema 7 years ago

nice spot! poor cute vole though!

Jellis 7 years ago

Thank you Tiz. I didn't know the location I found it would be the overlap of three species and over time came interbreeding.

Tiz 7 years ago

What an interesting spotting, and great timing! Good to read that it is not toxic to humans, as well as the rest of the information you added :)

Jellis 7 years ago

They figured it could be a intergrade but they still didn't think so because of the vole. Intergrades diet was mostly frogs, newts and fish.

Jeff Dreier
Jeff Dreier 7 years ago

A few years ago during a survey for another species, I found a very similar gartersnake in a drainage pond created by a landslide just east of your sighting (and northeast of the quarry). At the time, I concluded it was an intergrade aquatic gartersnake. I will try to find the photo and post it.

Spotted by

Vallejo, California, USA

Spotted on Mar 16, 2014
Submitted on Mar 18, 2014

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