“I see a garter snake in my yard once in a while,” an editor once complained to me, “but it’s never doing anything.” It’s true that snakes live about as privately as sizable above-ground, day-active animals can live, and most people pass a lifetime – many contentedly – without witnessing any of the really interesting stuff.
Sex, for example. Love-making for most snake species is a calm and dignified affair, but garter snakes have a better way. Males leave the communal winter dens – anything from rodent burrows and anthills to rock fissures and old farm wells – in early spring and simply hang out. Females emerge later, a few at a time, and immediately become the object of multiple attentions. The resulting “mating ball,” a writhing mass of 10 or 20 or more intertwined and feverishly preoccupied snakes, creeps blindly forward like a slow-motion rugby scrum.
It’s a miracle that pregnancy ever occurs, given that the unique snake anatomy makes sex almost impossible. And it isn’t just the lack of limbs. Male snakes are saddled with a primitive double copulatory organ – the hemipenes – which, under normal circumstances, lies inside of the vent through which it must protrude for mating, and pointed the wrong way! The garter snake solves this anatomical fix with breathtaking ingenuity. Through a combination of propulsor and retractor muscles attached to each hemipenis, one or the other achieves protrusion via eversion: the organ literally turns itself inside out in order to leave the body and connect with a female.
Like some mammals during rut, garter snakes do little or no feeding during the extended spring revelries, nor do they when they gather again near the winter dens in fall. Summer, on the other hand, is all about eating, and garters – unlike sit-and-wait opportunists such as rattlesnakes – are active foragers. I have shadowed garters on these hunting forays. An animal’s strategy is simply to meander about the landscape at half-speed – the head raised and swinging from side to side, steely eyes alert, tongue flicking – the animal insinuating itself through (and over, and under) grass clump and duff and blowdown and rock pile in that uncanny serpentine silence. Garters use both conventional smell and the chemoreceptor-rich roof-of-the-mouth Jacobson’s organ to trail prey, but mostly they score by simply bumping into a victim. And they nearly have to bump into it: a snake hears little of use on the hunt, nor is its eyesight acute. It may well fail to notice a motionless frog a foot away.
While some of North America’s 13 species of garter snakes hunt a particular habitat for particular prey, the common garter, among others, is a generalist. It explores streams, marshes, woods damp and dry, mountain slopes, fields and meadows, parks and residential areas, where, in addition to the staples (usually worms and amphibians), it feeds opportunistically on fish, leeches, small birds and rodents, and insects. Garters don’t always get much to eat, but since they slow their metabolic rate when inactive, they don’t require much. Indeed, physiologists have determined that during the active season a Vermont snake needs only about one-twentieth as much food as a same-weight mammalian predator.
Most people think of the Thamnophis as small snakes, and several species are. But most of our garters are medium-sized snakes, and females of our common garter may exceed four feet in length. Unlike birds and mammals, reptiles grow – though slowly after reaching sexual maturity – all their lives, and the reason most of us never encounter a large garter snake is that few live long enough to attain much size. A population ecology study in Kansas determined survivorship rates for the common garter at 36 percent for the first year and a constant 50 percent after adulthood is attained at two years. Of 100 newborns, then, something like 18 survive two years and only a single individual lives to age six. So much for large – read teenaged – garter snakes.
What happens to the unfortunate 99 during those six years? Coyote, fox, opossum, the weasel tribe, and domestic animals (dogs, hogs) all kill snakes, as do crows, herons, and hawks. (American kestrels feed large numbers of garters to their young.) Snakes feed on snakes as well, as do turtles and fish. The northern winter poses additional problems. Some young snakes fail to locate safe hibernacula, and dehydration – more so than cold – is a constant threat in the best dry winter dens.
Then, of course, there are humans, whether in the guise of a shopping-mall developer or ophiophobic suburbanite or country dweller with a spade. Or inattentive (even malevolent) motorist. Reptiles and amphibians have never been much good at figuring out roads, and while frogs and salamanders take their big hit while moving to the breeding pools during spring rains, snakes take theirs during the lazy days of October, when too many innocently bask on sun-warmed roads near winter dens.
Discussion *