Monitoring Eastern Indigo Snakes – I Have Only Been Bitten Once

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From six feet I zoomed in on the head of the 87 inch Eastern Indigo Snake, attempting to focus on his clear bright eye. A new and still damp shed skin stretched across the sand just outside my frame. I got closer. The snake had not moved from his looped position, but he was staring back, and now his mouth was slightly ajar. If a snake could look peevish, he did—I could have sworn he was giving me the stink eye. Suddenly, he awakened with a flourish, inflated the scales behind his neck, and began to hiss loudly.

This marked the third capture—the first in January 2012—of this impressive (7 foot, 3 inches, and 8 lb.) male Indigo. This observation was an unforgettable encounter—in the grey morning light, air heavy with coming rain (which may have prompted him to shed) – the snake was stunning. His muscular body, now glass smooth, his color a rich coal, or iridescent raven-black. Interestingly, he hasn’t grown an inch since his initial capture, hinting that he is probably full-grown. Socially, he may be the ruler of this vast Ohoopee River sand ridge. Put another way, on each occasion I have found him he was sharing burrows with adult females!

On the tree of snakes, within the Family Colubridae, Eastern Indigo Snakes (of the genus Drymarchon; 4-5 recognized species) are closely related to the racers and coachwhips (genus Coluber). In his magnificent book, The Amphibians and Reptiles of Costa Rica, Jay Savage describes the Indigo (in this region called the “Cribo”) as “a powerful, terrestrial racer”. Yet, Eastern Indigos, generally regarded as among the most docile of snakes, are much less prone to bite us, when compared to both Black Racers and Eastern Coachwhips. Most of us herp enthusiasts would rather walk barefoot across a field rank with sandspurs and fire ants than hand-grab a sun-warmed Black Racer.

Of course, one can’t help but wonder, “Why don’t Indigo Snakes bite us”? Could it be that their large size, combined with the diverse repertoire of defensive behaviors they perform (see below) often succeed in deterring predators and that biting isn’t even necessary?

This field season we are collaborating with other teams of investigators that also conduct mark-recapture studies of Eastern Indigo Snakes in Georgia to examine the varied defensive behaviors that Indigos may display when encountered in the wild. This study neatly dovetails into the long-term, mark-recapture studies we conduct as part of our Eastern Indigo Snake monitoring program.

For each Indigo Snake capture event, we’ll immediately record the cloacal temperature of the snake, since it’s likely that the body temperature of the animal influences the degree or intensity of the defense response. Our data-sheet lists the following defense behaviors that Indigos commonly display when captured: a) hissing; b) flaring of the neck scales; c) rattling the tail; d) musking, and; e) feint-striking. Other responses that very seldom occur include death-feigning and biting. We’ll also record whether the Indigo was found close to another Eastern Indigo Snake. From capture-to-release, it only takes us about 5-10 minutes to process an Indigo Snake (i.e., weigh, measure, mark, sex, photo), and we actively strive not to unduly stress any of our charges.

Intriguingly, when threatened, Indigo Snakes often strike with their mouths closed, or strike such that when they do come into contact with their human target, they refrain from actual biting. We refer to this as a “close-mouthed” or “feint strike”. This behavior is not well-detailed in the literature or mentioned in most species accounts. I first experienced this when I reached under palmettos to lift a well-nourished 7-footer, named “Lover”—who was on the ground next to his mate. His response was to hiss and repeatedly launch himself open-mouthed directly at my face (could this be related to mate-guarding, I now wonder?). Those seemingly slow-motion strikes always missed me. Whew, I was shaking (as was his tail).

Hissing by an Indigo amounts to passing air over the glottis, like a Pituophis (bullsnake or pinesnake). I’ve heard monster male Indigos do this when engaged in ritualized combat!

As you may know, I have only been bitten once by an Eastern Indigo Snake in the wild, and I have handled something like 411 different individuals. Finally, when a massive Altamaha River ridge Indigo known as “Big Fella” bit my thumb last year, it was a noteworthy event. It felt like a razor-blade-lined vice, and I half-expected to look down and see my thumb gone. I wouldn’t want to be a rattler in the maw of a hungry Indigo. “Big Fella”, who has been captured in each of the last five winters, carries his brutish girth with a charismatic presence known to enormous Drymarchon. Holiday Season is a good time to reconnect with old friends—having seen fresh sign of this big snake a few days ago I’ll bet we might re-acquaint again soon.

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