Answers

What’s this snake?

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The garter snake that Laura Bamford found was a darker, less fancy version than this off-Island fellow. Garters on Martha's Vineyard, Matt Pelikan proposes, may have evolved so that their markings help them hide among plentiful oak leaves. — Photo by Matt Pelikan

The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it to onisland@mvtimes.com.

Dear Matt,

We spotted this snake near the Farm Neck golf course in Hart Haven. Do you know what it is? We pushed it off the road so it would not get run over.

Laura Bamford

The snake Laura photographed is a garter snake, the most common (or at least the most commonly encountered) snake on Martha’s Vineyard. (Garter snake taxonomy is a frightful mess, and depending on what biologist you’re talking to, our garter snakes can be called either Eastern garter snakes common garter snakes. There are a variety of other garter snakes found across North America, with the relationships among them not well understood.) A medium-sized snake, rarely exceeding three feet in length in my experience, this species is widespread on the Vineyard; in particular, it seems to tolerate human activity fairly well, and as far as I know is the only one of our snakes likely to turn up in densely settled residential areas.

Garter snakes have a preference for damp habitats, but are quite flexible in their ecological requirements; likewise, they are versatile hunters, taking anything from earthworms to frogs to mice. Like all of the Island’s snakes, they are considered non-venomous, thought their saliva contains chemicals that may be toxic to some of their prey species and, according to some accounts, slows the clotting of blood. Given their role in regulating small rodent populations, the garter snake is a beneficial animal that should be welcomed wherever you find it. Like all of our snakes, garter snakes have suffered from road kill and predation by skunks, raccoons, and cats.

This is generally a docile species which often doesn’t try to bite even when you handle it (though they do have teeth — and a large one, if sufficiently annoyed, is capable of giving a pretty good nip). A more likely response when garter snakes are disturbed is release of a burst of foul-smelling musk from glands near the anus, and/or defecation on whoever is disturbing them.

Garter snakes may live for a decade or more if they escape being eating or getting mashed by an automobile. They overwinter, often in groups, by hibernating in dens, which are generally rocky sites such as old foundation, stone piles, or pits of debris. In warm weather, this snake is active day and night, and it is generally not hard to find one on the Vineyard.

The one Laura photographed, largely brown with a sort of checkerboard pattern, is typical of the garter snakes one finds on the Vineyard. But over its wide geographic range, our garter snake (whether one calls it Eastern or common) is a surprisingly variable animal. In some populations, these snakes are marked with yellow and black bands, resembling the closely related ribbon snake, which is also quite common on the Vineyard. This striped pattern is evident on typical Vineyard examples like Laura’s, if you look carefully, but the yellow strips are muted almost to invisibility by brown markings.

The distinctive appearance of our garter snakes may reflect the geographic isolation of our population during the five thousand years or so that the Vineyard has been an island. My own hypothesis, which is probably all wrong, is that the dominance on the Vineyard of oak trees, which shed brown leaves which are very slow to decay, may have led our garter snakes to evolve markings that help the snakes hide among fallen oak leaves.