by Whit Gibbons

July 27, 2014

Every plant and animal species in the world has secrets, and scientists who explore the intricate and intimate details of their private lives help solve ecological mysteries. J.D. Willson, a faculty member at the University of Arkansas, told me of an amazing biological observation about a little snake.

J.D. completed his doctoral work with the University of Georgia’s Savannah River Ecology Lab. He conducted his research on the Savannah River Site in Aiken and worked on a project involving the capture of more than 3,000 snakes. Most of them were black swamp snakes.

These small, secretive, seldom-seen aquatic creatures weigh in at less than 1/10th the size of the big watersnakes familiar to anglers and kayakers. Most herpetologists who have spent a lifetime working with reptiles have never seen a live one because they are uncommon in most areas throughout their geographic range.

Black swamp snakes have a name that belies their beauty. The back and sides are glossy black. The belly is brilliant red and can only be seen when the snake is turned onto its back. These inoffensive animals do not bite people, and even if they did, they are too small for it to matter. The largest one ever found was a little over a foot and a half long. Their prey includes leeches, small salamanders, tadpoles, and tiny fish. Swamp snakes remain in the water or mucky sediments almost their entire life and if not kept moist will quickly die.

J.D. and his colleagues capture aquatic snakes with a simple technique: minnow traps. These are small plastic cylinders with a funnel at each end that let fish, salamanders, and snakes enter, assuming they are small enough to do so. The traps are set with the top above water so that air-breathing animals like snakes do not drown in them. During sampling, J.D. sets 450 to 600 traps each day at one of his collecting sites. Although some of the animals may escape through one of the funnel openings, large numbers are trapped and then captured when the researcher checks the traps the next day.

After capturing a snake, J.D. uses a special branding technique that is not harmful to the snake. It gives each individual a unique identification code. The mark allows the individual to be recognized years later. Capture-recapture studies, as they are known, are used with many animals to determine how long they live, what their movement patterns are, and how fast they grow.

J.D. returns to SREL in the summers to continue his long-term studies on this fascinating little species of snake, and this summer he observed an amazing occurrence. Six years earlier he had captured two male black swamp snakes on the same day. He marked them for future identification after recording the usual information: length, weight, and where they were caught. During his summer sampling this year, he caught the same two snakes again.

Recapturing marked individuals is not unusual. In fact, of the 3,069 black swamp snakes he has captured, 1,506 had been marked since he began the study in 2003. He has recaptured 529 of these at least once. But these two recaptured individuals were different. He caught them on the same day, and neither snake had been seen since their first capture on the same day six years earlier! The odds of each being seen only twice, each time on the same day, are extraordinarily high.

Why the two snakes were recaptured on the same day after an interval of six years remains a mystery. Was it coincidence or are there as-yet-unexplained behavioral and ecological phenomena in operation? Continued study and comparisons with the timing of when other marked snakes are recaptured relative to each other may turn out to be revealing – whether the answer is simple coincidence or scientific phenomenon. The black swamp snake is just one of the species that scientists study in an ongoing effort to understand nature’s myriad and marvelous secrets.

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