Eastern Indigo takes on an Eastern Diamondback

On a remote pineland in south
Georgia, I was helping a University of Georgia doctoral student with her radio telemetry study of Eastern Indigo
Snakes. We were following the radio signal from the transmitter of a gorgeous 6-foot female indigo snake, when apparently our efforts to pinpoint her location
disturbed her; she fled deep into the burrow of an armadillo. This was around
noon on a very warm summer day, so to the drones of cicadas we broke for lunch,
checked for ticks and then got back to work. We decided to again check on the
female, and found that she had exited the burrow and moved several hundred feet
into a shady oak hammock, where we found her in the act of dispatching a 3-foot
black racer. The scene was graphic and intense … we could hear the teeth of the
indigo snake scraping against the head of her quarry. Then, suddenly she lifted
the limp racer like a mother would her pup and carried it a good distance,
before stopping and eating it headfirst. Within about five minutes, the racer
had disappeared inside the indigo snake. Such is a day in the life of a hungry
eastern indigo snake.

When asked, “What do indigo snakes eat?” I am tempted to
respond “What don’t they eat!” Recently, some colleagues and I co-authored
a scientific article that attempted to shed light on this topic. In this paper
(published in Southeastern Naturalist. 2010. 9:1-18), we compiled prey records
for the eastern indigo snake based on our field observations, the published
literature, dissections of road-killed snakes, and museum specimens.

  Enlarge PhotoEastern Indigo eating a gray rat snake

Launching this effort we already knew Drymarchon
couperi
, known as the “Commander of the Forest,” to
be an indiscriminate predator with a generalist diet — in short a species known
to consume a wide variety of prey. Even so, we were impressed by our results:
for the period 1940-2008, we compiled a 186 prey records for 48 different
species of prey! Anurans (frogs and toads), small turtles, snakes, and rodents
comprised 85% of these records.

Among the novel to downright weird prey items recovered from
indigos include a southern flying squirrel, a juvenile alligator, an opossum
and a siren (an eel-like aquatic salamander). One apparently very hungry indigo
was observed in the dunes behind a Florida beach ripping tissue from the head
of a dead shark! And sometimes snakes go on feeding binges: a large adult
found on Fort Stewart, Georgia, contained a southern hognose snake, a pigmy
rattlesnake, a toad and a hatchling gopher tortoise.

Now for the cool part: our research confirmed 24 different
types of snakes as indigo prey, and this figure includes all six venomous snake
species native to the southeastern U.S. (coral snake, copperhead, cottonmouth,
timber rattlesnake, eastern diamondback rattlesnake, and pigmy rattlesnake).
Pit vipers, in fact, are frequently consumed. This raises the question, how
do indigo snakes subdue and handle dangerous prey like rattlesnakes?

  Enlarge PhotoToad. It’s what’s for dinner.

When indigos find a snake they wish to eat, they first go
straight for the head, followed by repeated biting and chewing (while using a
powerful body coil to press the prey to the ground), employing strong jaw and
neck muscles to efficiently subdue and immobilize their unfortunate snake
victims. Indigo snakes are not constrictors (i.e., snakes that suffocate their
prey by squeezing them, such as kingsnakes, pine snakes, boas, and pythons) but they rely on their powerful
jaws to subdue their prey. Invariably, snake prey are
swallowed head-first. So, when indigos take on pit vipers, most often
they are never bitten. Indigo snakes are not wholly immune to pit viper venom,
but if they are bit, they seem to suffer only negligible effects. One
herpetologist reported small blisters on the flanks of an indigo bitten by a
copperhead, but the indigo recovered without incident. In fact, indigo and kingsnake immunity to snake venoms is a subject in need of
further study.

Indigo snakes are what
herpetologists would call an active forager. They travel widely and actively
search to locate their prey, much like other snake species including racers and
coachwhips. The same adult might prowl a wetland
margin one day and probe the interior of some tortoise burrows and stump holes
the next. This is in contrast with an ambush forager or a snake that hunts
primarily by waiting for its prey to come to it. Many species of vipers provide
good examples of a “sit-and-wait” predator. We concluded our indigo snake prey
paper by mentioning that the varied diet of the eastern indigo snake allows the
snake to forage successfully in many different habitats, and under fluctuating
environmental conditions — a valuable characteristic for a top-level predator
that requires a large home range.

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