Tuesday, June 19, 2012

GARTER SNAKES


No, they're not "gardner snakes" or "garden snakes." They are garter snakes, named after the striped garters that embellished many a lady's leg in the distant Twentieth Century. A snake that bites, thrashes around, and emits a foul-smelling fluid when handled probably wouldn't make a very good garter, however.

The first stage of predator avoidance is to flee, and snakes—notwithstanding their lack of legs—are superb at that. If not entirely out in the open, as for example when they cross roads, they quickly disappear into the vegetation when disturbed. If captured, the larger ones have no hesitation about biting to defend themselves. A bite from the many sharp teeth of just about any snake will bring out a series of four-letter Anglo-Saxon words such as "ouch" and "rats."

Whether they bite or not, some snakes are sure to wind their body around the captor (or the captor's arm, in the case of a human) and discharge a smelly fluid consisting of mixed feces and urine and a musk produced in the cloaca. If you must catch one, securing the tail is just as important as grabbing the head.

Most garter snakes have a middorsal pale stripe and a pale stripe low on either side. No other common northwestern snakes share that pattern. Although the scales on their underside are smooth, garter snakes have keeled dorsal scales, which gives them a rough appearance and feel. They are rarely more than three feet in length, and most are much smaller.

There are three common species of garter snakes in the Pacific Northwest, but there is sufficient variation in all of them that identification is not always easy.  The Common Garter Snake (Thamnophis sirtalis) occurs all across North America. The ground color is dark, with the typical light stripes. Our populations usually have red spots along the sides, but the darkest individuals can show very little red; look closely. In western Oregon and southwestern Washington, the head is largely reddish.

Western Terrestrial Garter Snakes (Thamnophis elegans), widespread in the West, never show any red markings. Populations in our region characteristically show a series of alternating dark spots in a checkerboard pattern on a lighter ground color, still with the normal three stripes. There are melanistic populations in the Puget Sound region, some individuals almost entirely black.

Northwestern Garter Snakes (Thamnophis ordinoides) are restricted to the Pacific Northwest, mostly west of the Cascades. They are smaller than the other two species, with a relatively smaller head. The head is somewhat lighter than the body, with a contrasting dark stripe through the eye. This species is very variable, from very dark with contrasty yellow stripes to a lighter color with dark markings not so different from those of a Western Terrestrial. Some individuals have a red dorsal stripe or are largely reddish above, unique to this species.

Common and Western Terrestrial Garter Snakes eat mostly vertebrate prey, especially fishes and amphibians, but both may take any other small animals that they come upon. Because of their primary diet, they are commonly found around water, even in it (notwithstanding "Terrestrial" in the name). Northwestern Garter Snakes are invertebrate feeders, capturing mostly slugs and earthworms. This correlates with their smaller head and mouth and entirely terrestrial existence.

Garter snakes are common throughout the warmer parts of the year. They disappear by October, sheltering underground where possible. Sometimes numerous individuals den together, perhaps conserving body heat by being tightly packed. They are often the first snakes to appear in spring, sunning themselves in exposed places near where they spent the winter in dormancy. Like all reptiles, they use the sun for thermoregulation.

Garter snakes are the only common snakes in the wetter parts of the Pacific Northwest, and they are often found in suburban parks with natural habitats remaining. Their continued presence is a great reason to preserve those habitats.

Dennis Paulson

8 comments:

elizebeth said...

I recently came across your blog and have been reading along. I thought I would leave my first comment. I don't know what to say except that I have enjoyed reading. Nice blog. I will keep visiting this blog very often.

Alena

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Slater Museum of Natural History said...

Thanks, Elena. There aren't a lot of comments, so I don't look for them most of the time, but any like this are appreciated.
Dennis

Dean Adamo said...

We have a garter snake living in a crack between our back cement steps and the house, near a rockery and some ground cover. The kids have named him "Sam the Snake"
The odd thing that I am curious about is that he actually hangs out and lives with a small salamander...I mean they really seem to be friends...it's the oddest thing I have seen. Is this normal?

Anonymous said...

I Need Some Help. I Have A Very Small Snake Living In My Semi Truck. I Don't Know The Kind Or If Poisons So Can You Help.It Is Green With Red Spots The Spots GO AcrossThe Body And Are Just Behind The Head To Its Tail.CAme With Truck

Jim Bergren said...

I recall the Reptile Man coming to our school for an assembly. He taught us how to identify non-venomous to venomous snakes by colour. He said, Yellow over black, he's an okay fellow. Red over black, you're dead, Jack. I live in Vancouver, Washington in the PNW and to my understanding we do not have any venomous snakes in this part of the region. Today on my walk I saw a (what I believe to be)red striped Garter Snake. Does the Reptile Man's saying apply here? Red over black, you're dead jack? Please advise. Jim

Amma said...

We were able to observe a garter snake devouring a slug in our yard today. It was fascinating and my oldest granddaughter was attentive to the event. My question is about the coloring of this particular snake. He was dark with dark tan stripes, really beautiful. Looking up different types, I couldn't find this particular coloring. Any ideas? We live in Enumclaw.

Anonymous said...

I grew up in West Vancouver, on Vancouver's North Shore in the 1960's. At that time we would regularly see Garter Snakes in our garden. I still live on the North Shore and never see them anymore. Does anyone know why they've disappeared?

Unknown said...

I used to live in Washington, grew up there, both sides of the mountains. I loved catching snakes. I was told at a young age that that snake you are describing was called a Red Racer, later learned it is just a dorsal striped Garder. They are not poisoness, just very aggresive with bigger teeth. That old color rhyme saying is a warning about the most venomous snake in America called the Coral Snake that can be confused with a couple types of Milk Snakes and King Snakes which are completely harmless and make great pets.