Waking Snakes: Discovery of a Nantucket Snake Hibernaculum

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

As I write this, the world is celebrating the 42nd Earth Day. Today’s story is a fitting tale of the entanglement of man-made and animal realms. Fortunately for all concerned, it has a happy ending. Wintertime is a time of hibernation for many of us. We move slower, stay in more, and try to stay warm. Many animals hibernate to conserve energy and increase their chances for survival.

snakes on Nantucket

A new state-of-the-art septic system is being installed at the UMass Boston Nantucket Field Station, and during the construction phase we discovered two large, six foot deep, six foot wide, underground cisterns. To our even greater surprise, when we opened the lids of both cisterns (which were connected by a ceramic pipe), we found a nest of milk and garter snakes bedded down for the winter. The name for this phenomenon is a hibernaculum. This word comes from Latin word “hibernare” (to spend the  winter) or “winter quarters.” Hibernaculum is also used in biology to describe a protective case,  covering, or structure, such as a plant bud, in which an organism remains dormant for the winter.

Previously in this column, we explored the life histories and stories of the six species of snakes found on Nantucket. You may recall that snakes are “cold blooded” creatures, or ectotherms (from the Greek  “ektós” for “outside” and “thermos” for “hot”). Ectotherms control their body temperature through external means from basking in the sun to cooling off in the shade. Lucky for us when we had to become inadvertent snake wranglers, cold-blooded animals are very sluggish in cold environments. Their metabolism decreases significantly when it is cold, allowing them to survive on much less food and water and extending their chances for survival. Unfortunately for us, wintertime is a time of food and holidays and our endotherm nature doesn’t help one bit for lowering our appetite when it gets cold.

Most of us have heard of the term “snake den” and some scientists refer to these as refugia. All of these words are used to describe the places where many snakes spend the cold months of the winter and at times, the extreme heat of summer. Hibernacula can range in form from natural structures such as caves and sinkholes to man-made structures such as foundations, crawl spaces and garages. Although seemingly very different, these structures have one thing in common; they provide a thermally stable place for snakes to hide while the temperatures are too extreme for activity.

snakes on Nantucket

Before I forget, I have to mention the extreme bravery my husband Len Germinara exhibited when we found these snakes. It appeared we would be removing these underground cisterns by breaking them up and pulling the pieces out of the ground to make way for new septic tanks. We knew we had exposed these snakes to the cold and that we needed to pull them out and figure out a place to repatriate them that would allow them a couple more days of warmth. Using “grabbers” which are  extension pickers we use for the CleanTeam, Len was able to pull out each of these snakes, some quite  long and large and place them with some towels into a bucket. Fortunately the snakes were definitely cold and moving slow and were quite content to be covered by a towel. When gently handling them, Len was amazing by the muscular strength and grip of the larger milk snakes. Lots of people are frightened by snakes, and there weren’t many volunteers among the construction and archeology workers at the site.

We are fortunate to have a resident snake expert on island, Andrew McKenna Foster, the Director of  Natural Science Department at Maria Mitchell Association. I called Andrew, and he came over within 30 minutes. We had released two milk snakes, but still had 10 milk snakes and two garter snakes. He was able to positively ID the snakes, weigh then and measure their lengths and try to determine the gender of the snakes, which is not easy. There are two ways to do it, one involves a probe and as this is a family show, I won’t go into details. The other method is relatively easy when snakes are fat and happy, but  these snakes had not been eating for some time. Because the male parts are located just inside the cloaca opening (the exit point for waste and reproductive fluid) males have a tail that is thicker and longer than in females, and also tapers less evenly to the tip (thicker for a bit then suddenly thinning). Females have a tail that is thinner and shorter than in males and tapers smoothly, evenly and more quickly. But allof these snakes were skinny and hiding their genders because they have not eaten.

snakes on NantucketAndrew was extremely excited to learn about this discovery and informed me that this is the first
documented case of a verified snake hibernaculum on island. When you think about some of the  historical accounts of snakes on island, it makes sense to find a hibernaculum near the Field Station. You may have heard about “Rattlesnake Bank” which is off Polpis Road near the Lifesaving Museum right across the marsh from the Field station. The name comes from a local who saw what he believed  to be a rattlesnake but who was most likely misidentifying a milk snake (which also rattles its tail) for  the dreaded rattlesnake. Somewhere on island was an area called “Snake Spring” where Nantucket’s  English settlers dispatched hundreds of snakes as they emerged groggily from their inter home. We have come a long way from the days of fear and loathing of snakes.

There are six species of snake found on Nantucket: garter snake, ring-neck snake, eastern milk snake, northern water snake, ribbon snake, and smooth green snake. All of these snakes are non venomous and cannot seriously hurt you. Most of the snakes we found were milk snakes which are a boldly patterned and quite beautiful snake as you can see from the accompanying picture (photo by Len Germinara). The milk snake (Lampropeltis triangulum) has a light gray to tan body covered with  reddish-brown blotches bordered in black. Larger blotches on the back alternate with smaller ones on each side. The head is patterned, usually with a light colored “Y” or “V” within a reddish brown patch. Smooth scales give this attractive snake a shiny or glossy appearance. The belly is patterned with an irregular checkerboard of black on white.

snakes on NantucketGenerally, you can recognize this most common of all New England snakes, the garter snake (Thamnophis sirtalis) by its pattern of yellow stripes on a black or brown background. Stripes may be tan, yellow or orange. Nantucket garter snakes have a darker coloration and can be more reddish brown on top to better camouflage themselves in our coastal habitat. There are folks out there who build snake hibernaculums for snakes in order to protect them in areas of construction or  development. And I managed to find a couple of web sites that talk about constructing experimental snake hibernaculums. It just so happens that these cisterns are the perfect refuge for snakes. We were able to leave these cisterns in place to shelter the snakes over the incoming winters as they will most  likely come back to the same spot next year. I promised you a happy ending. We released the snakes appropriately on Saint Patrick’s Day which was warm and sunny. We placed the larger ones some distance from the smaller ones and made sure we released them close to food and water. The snakes were happy to be free of their pillowcase enclosures and were much feistier in the warmer air.

Read more about recent snake research on island here and at www.yesterdaysisland.com/2010/science/11-special2.php. The research is funded by the Nantucket Biodiversity Initiative which is a partnership between Nantucket conservation organizations, universities, non-governmental organizations, and individuals interested in documenting the biodiversity of the islands and adjacent waters and  monitoring and conserving that biodiversity over time. Members of the NBI include: the Linda Loring Nature Foundation, Maria Mitchell Association, Massachusetts Audubon Society, Nantucket Conservation Foundation, Nantucket Garden Club, Nantucket Islands Land Bank Commission, Nantucket Land Council, Natural Heritage & Endangered Species Program of Massachusetts Division of Fisheries & Wildlife, Science Department of Nantucket High School, The Trustees of Reservations, the
Tuckernuck Land Trust, and the University of Massachusetts Boston Nantucket Field Station.

I bring up the NBI to get everyone thinking about and planning to attend the NBI’s 5th Biennial Biodiversity Assessment Week which is May 16-22. Biodiversity Week is a week-long series of walks, talks and events to celebrate and explore the unique biodiversity of Nantucket. There are events for children, the general public, researchers, and naturalists. Kit Noble will be showing his film “Nantucket by Nature” on Wednesday May 16th at 6 pm in the Great Hall at the Nantucket Atheneum to kick off the start of Nantucket Biodiversity Assessment Week. Our keynote talk by moth and bee expert Dr. Paul Goldstein entitled “”Beyond Bees: Pollinator diversity and invertebrate conservation on the Cape and Islands” will be on Friday May 18 at 7 pm in the Great Hall of the Atheneum.

Field trips will include morning and afternoon programs on insects, plants, shorebirds, moths and butterflies, bird song, marine life, and more. Great Point tours will be offered by the Trustees of Reservations. Family oriented programs will also be offered in the areas of insects, shorebirds and plants. In addition to the kickoff and keynote, evening presentations will be made on insect signs and insect tracking, the offshore underwater world, and Nantucket’s natural history. A photography contest that is open to everyone will be held with the winners in each category announced at an event to wrap up the week’s programs on the 21st at the Nantucket Conservation Foundation. I hope to see you there and that you have emerged refreshed from your own hibernaculum.