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

SOME SNAKES ARE SHARP, SOME ARE DULL

This is most apparent if you look at the ends of their tails.

The Sharp-tailed Snake (Contia tenuis) epitomizes the sharp end of the spectrum. The tip of its tail, really the last scale on the tail, is quite sharply pointed. This small and secretive snake is usually found under logs or rocks, and it presumably comes out at night, when it hunts for its primary prey, slugs. Oddly, one of the most commonly observed prey species is an introduced slug, and one wonders what they ate before the introduction!

It may be that the sharply pointed tail tip is handy for subduing slimy prey, but it also has been speculated that it may be used against predators (a snake may press it into the hand of a human captor) or even as an aid in burrowing. All pure speculation, of course, but we assume there must be some adaptive function of this prickly tail.

It has also been suggested that the banded pattern on the snake’s underside, sometimes exposed, may mimic the banded pattern of several millipede species of the area. As the millipedes are toxic and distasteful, some Sharp-tailed Snakes may escape predation by this mimicry.

Few people see this interesting snake, as its range is very restricted in the Pacific Northwest, and it appears to be active only for a relatively short time in spring and fall, when it is warm enough for reptile activity yet cool and moist enough so this small species isn’t stressed by low humidity. April and September are good months to look for sharp-tails by looking under objects on the ground that may serve as hiding places. Be sure to replace them carefully.

Rubber Boas (Charina bottae) are at the other end of the spectrum, with an extremely blunt tail for a snake. One of the consequences of this is that it is difficult to distinguish the head end from the tail end, and this may be the whole point, as it could be an effective anti-predator strategy. A snake captured by the wrong end might be more able to escape, and, if inclined, might even bite the predator. The latter seems unlikely, as these snakes are extremely docile, at least when picked up by a human.

Rubber Boas are much more common and widespread in the Northwest, usually associated with open conifer woodland. They are active all summer and take a wide variety of prey, mostly small mammals but also other vertebrates. They are active at night during much of the summer, but on cooler days especially they may be seen out and about. Otherwise, you look under rocks and logs, just as you would to find Sharp-tailed Snakes. A fortunate naturalist might find both of them together!

Dennis Paulson

AMPHIBIAN DEFENSES

One reason that amphibians in general are in trouble (well, with the exception of Bullfrogs and Cane Toads) is that they have very porous skin, so they are more likely to pick up environmental contaminants than are other vertebrates. The chytrid fungus that is killing so many of them attacks their skin, perhaps interfering with dermal respiration or water balance.

Thin-skinned and small, it would seem that amphibians would be almost defenseless against the whole array of predators with which they share their world. But they’re not!

In part because of their sensitivity to drying out, most amphibians are nocturnal. But this also is a first line of defense against diurnal predators, among which birds are by far the most important. There are many hawks that relish amphibians, and in the tropics members of many different bird groups eat frogs. Of course, by being nocturnal, the frogs are subject to owl predation; you can’t win them all!

Many species, even though active at night, spend the day at least partially exposed, and they are usually very well camouflaged, green for the leaf-sitting frogs and brown for those on the forest floor.

Frogs are also escape artists. The great leap forward that a frog can take with its long legs allows it to capture prey very effectively, but the leap is probably even more important for predator avoidance. A Wood Frog (Rana sylvatica) at the edge of a pond heads for the water at the least disturbance, arcing through the air on the way there. Plunging into the water, it immediately makes for the bottom sediments, where it disappears.

Nocturnal life style, camouflage colors, and escape locomotion notwithstanding, amphibians are still captured. For many species, the next line of defense is provided by their skin toxins. Many of them secrete chemicals in the skin that are poisonous to other vertebrates. Sometimes these are concentrated in particular glands, often around the head (predators often grab their prey by the head to dispatch it most quickly). Note the big toxin-secreting parotid glands behind the eyes, presented to the potential predator by this Northwestern Salamander (Ambystoma gracile).

Many of these amphibians are nocturnal and cryptically colored. But others are either active in the daytime or can be found where they spend the day only partially hidden. Toad tadpoles are toxic, and instead of scattering out and hiding as do the tads of other frogs, they congregate into big, black, wiggly masses, and a predator that captures one and then spits out the bitter-tasting morsel can easily learn to avoid such groups.

These include many species of poisonous frogs, for example the Strawberry Poison-dart Frog (Dendrobates pumilio). Many of these species are conspicuously, even garishly, colored. This is warning coloration (also called aposematic coloration), and predators that learn not to bother with this prey presumably leave more descendants.

Rough-skinned Newts (Taricha granulosa) of the Pacific Northwest are cryptic brown when viewed from above, but when disturbed, they display their bright orange undersurface as a warning coloration. These newts are extremely poisonous and have killed people who swallowed them (just on a dare, can you believe it?). The tetrodotoxins in their skin are poisonous to just about anything that tries to eat them and in fact are among the deadliest poisons known to have evolved.

But some populations of Common Garter Snakes (Thamnophis sirtalis) have evolved resistance to this toxin and can eat the newts with no ill effects! This “evolutionary arms race” has been won by the snakes in this case, but not in all populations.

Dennis Paulson