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Tuesday, April 9, 2013

Fork in the road

Finally, a real snake for the Year of the Snake!

This garter snake was basking in the warm sun on a gravelly road on Bodega Head today.  I was excited to get a few pictures including one showing the forked tongue (above).

Here's the whole snake.  It was over 2 feet long.

A close-up of the body shows the handsome color patterns and the keeled scales.  Note how each scale looks like it has a thin line running down its center — that's the keel.

Now here comes the tricky part.  I think at least two species of garter snakes have been recorded on Bodega Head.  One is known as a California Red-sided Garter Snake (Thamnophis sirtalis infernalis) — it's a subspecies of the Common Garter Snake.  The second is known as a Coast Garter Snake (Thamnophis elegans terrestris) it's a subspecies of the Western Terrestrial Garter Snake.

So is this a California Red-sided Garter Snake or a Coast Garter Snake?  One important feature to look for is the number of upper labial scales (labial = lip).  Red-sided Garter Snakes most often have 7, while Coast Garter Snakes most often have 8.

Here's a side view of the face so that you can count the labial scales.  Start with the one below the nostril and then count towards the tail until there's a dramatic change in scale size (all of sudden they become much smaller). 

What number did you get?

Don't worry if this is confusing at first.  I'm not always sure I've done this right, so here's an example of how I counted (the scales are numbered below).

Because it appears there are 8 labial scales, I checked to see if there were other features that might confirm this as a Coast Garter Snake.

Another helpful characteristic is the shape of the internasal scales.  This is just what it sounds like — internasal = between the nasal openings or nostrils.  In Coast Garter Snakes, the internasal scales tend to be wider than long, and rounded (not pointed) at the front end.  The next image shows the two internasal scales (see arrow).

It does appear that the internasal scales are broad and rounded.

I also read that Coast Garter Snakes often have red or orange flecks within the yellow side stripes and on the belly.  So I checked for that, too.

You can probably guess that I'm leaning towards this being a Coast Garter Snake.  But I'll also be the first to admit that I don't have much experience separating these two species, so let me know if you disagree!

1 comment:

Leth Benz said...

ha i get it fork in the road :)