Tuesday, June 19, 2012


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

Friday, June 15, 2012


We have lizards in the Pacific Northwest, but like all other reptile groups, they become more common and diverse as you travel lower in latitude. In the southwestern deserts, lizards often dominate the landscape, if you exclude the ever-present and noisy birds.

Lizards seem among the most heat tolerant of any vertebrates. You walk around in the desert when it's so hot you really shouldn't be out there, and you find lizards running ahead of you across the burning sand. Most of them are long-legged, and they hold their body above the substrate as they move. The really fast Zebra-tailed Lizard (Callisaurus draconoides) can run bipedally, using only its hind legs for a slightly greater speed. They have been clocked at four meters per second, and they seem to blur as they run. As your eyes follow them, you may not see that they stop.

The long legs and toes, especially the hind ones, are what furnish the combination of speed and sand traction that these lizards need to move about. All of their needs are met by high speed: predator escape, prey capture, and quick moves from shade to shade. Try chasing one down. None of the lizards shown here does much climbing except the Lesser Earless Lizard (Holbrookia maculata), which moves around on rock faces or up in low shrubs.

One adaptation shared by all these lizards to avoid the hot desert sand is to contact it as little as possible. One way of doing this is to rest on their heels and flex their toes upward. Perhaps their toes are especially heat-sensitive. And if you keep watch, you'll see that these lizards usually head for shade in the middle of the day. They're not that heat tolerant!

Earless lizards are unique in lacking external ear openings, perhaps an adaptation to keep sand out of the ear. Oddly, the closely related Zebra-tailed Lizard and fringe-toed lizards (Uma) have ear openings, yet they spend even more time on the sand. Maybe earless lizards just like silence!

The heads of the Zebra-tailed and Lesser Earless lizards are somewhat scoop-shaped, widest at the mouth. They push their head into the sand and, by digging with alternate strokes of the legs, bury themselves very quickly to avoid predators or spend the night.

Most of the lizards of the desert eat arthropods, with two rather different modes of foraging for them. The common mode is as a sit-and-wait predator. The lizard remains in one spot and watches around it. If it sees an insect or spider, it runs and grabs it. The Leopard Lizard (Gambelia wislizenii) is large enough to take other lizards as prey.

The other mode is as an active searcher. This characterizes the whiptail lizards of the genus Aspidoscelis (formerly Cnemidophorus). They move slowly along, digging in the soil with alternate front legs, and scare up or unearth their prey. They are just as fast on the go as the other types, though. The striped pattern helps them disappear when they move into dense cover. As in striped snakes, the animal doesn't seem to move when you see only part of it.

One of the lizards shown here, the Desert Iguana (Dipsosaurus dorsalis), is a herbivore. Typically it takes leaves, flowers and fruits of the low shrubs that are common in its arid habitat. Note its blunt head, not so different from the big green iguanas of the tropics.

Check out the southwestern desert in summer, the lizard season, but be sure to bring water!

Dennis Paulson