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Volume 38 Issue 5 • May 29 - June 4, 2008
now in our 38th season

Snakes Alive! - Snakes on Nantucket

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

Ever since St Patrick allegedly drove the snakes from Ireland, mankind has always had an uneasy relationship with the idea of snakes on an island.  In reality, except for in zoos and as pets, there are no snakes on Ireland and there probably never were.  Many islands around the globe do not have snakes because these islands separated from the mainland before snakes evolved and migrated out of the tropics onto the separating land masses.  Although Nantucket does not have the variety of snakes that can be found on the mainland, we do have six species of non-poisonous snakes on our little home in the ocean: the ribbon, garter, northern water, milk, ring-necked, and the very rare smooth green snake.

Snakes are cold blooded creatures, or ectotherms.  Cold-blooded creatures take on the temperature of their surroundings. They are hot when their environment is hot and cold when their environment is cold.  Cold-blooded animals are much more active in warm environments and are very sluggish in cold environments.  This is because their muscle activity depends on chemical reactions which run quickly when it is hot and slowly when it is cold.  To increase their body temperature, snakes will stretch out on dirt roads on warm, sunny days, so be especially careful when driving or walking our roads from late spring to fall.  This is the best way to see snakes, and two popular spots include the Nantucket Conservation Foundation properties of Squam Farm (off Quidnet Road) and the UMass Boston Nantucket Field Station roads and trails.  Please remember that they are not poisonous and will typically slither off to avoid human contact.  In the winter, most snakes will hibernate in burrows and their metabolic functions will drop significantly, which is remarkably similar to my wintertime activity level.


This northern water snake was nearly four feet long.
Photo courtesy Len Germinara

Snakes are an important part of our island ecosystem. All snakes are predators and they also serve as food sources for our hawks and other birds, including songbirds.  Depending on size and species, snakes may feed on invertebrates such as slugs, worms and insects, or on fish, amphibians, other snakes, birds, bird eggs, and small mammals.  Species such as the milk snake eat rodents, and their presence around barns is not only a good sign, but also the reason they are called milk snakes.  The milk snake regularly enters burrows and will consume young mice and rats right in their nests.  Our common garter snake acts as a “green” pesticide-free, landscape assistant by consuming garden pests such as slugs and certain soft-bodied insects.

Snakes find their prey by sight and scent, and sometimes by temperature. Except for burrowing species, snakes have excellent short-range vision.  Their extraordinary sense of smell is attributable to a harmless, constantly flicking, forked tongue that carries scent particles to a specialized sensory organ (Jacobson's organ) on the roof of the mouth.  Some species catch their prey by hunting it down, others through ambush, and, although it is not known for certain, most species probably scavenge dead prey as well.  Some species kill their prey through venomous bites, others by constriction, still others by simply overpowering and then swallowing their prey.  Lacking any chewing teeth, all snakes swallow their meals whole.  Depending on the size of the meal and the temperature of their resting habitat, our native snakes may eat as often as several times a day or as rarely as once a month.

Most islanders know about this story from Nathaniel Philbrick’s book Away off Shore (www.NathanielPhilbrick.com):

"The English were less than enamored of Nantucket's snakes, particularly in the eastern end of the island, where a snake was reportedly sighted 'as big round as a gallon keg' and eleven or twelve feet long!  Jethro Swain, a third generation Nantucketer, recalled how one sunny day in the early spring, a huge number of snakes, groggy with cold, were discovered near a natural spring still known today as Snake Spring.  According to Swain, the English 'mustered a company...that dug two holes, and with hay rakes they raked as many of them into the holes as they could -- about two cartsfull.' The English then set huge bonfires over the pits and 'as the heat caused the snakes to attempt to escape, they were driven back...until they were all subdued."

Some old-timers will also tell you about Rattlesnake Bank which is off Polpis Road near the Lifesaving Museum (look for a mailbox with the lettering “rattlesnake bank”). 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.

Scientists who study snakes and other reptiles and amphibians are called herpetologists.  You may have noticed plywood sheets around the island and on Tuckernuck. These have been installed for a Nantucket Biodiversity Initiative funded biological survey project to attract snakes in various habitats around the island by field biologist Scott Myers of Oxbow Associates with assistance from Maria Mitchell Association (MMA) research intern Rob Carr and volunteers from MMA and the Tuckernuck Land Trust.  Please do not disturb these cover board arrays.  Several times during the year, they are inspected for snakes lying beneath them; the snakes are identified, sexed, counted, measured, and tagged for mark-recapture experiments.  Snippets of their tails are sometimes taken for DNA analysis and a more thorough investigation of garter snake color variations is being conducted in 2008.  A video of the field studies done by Rob Carr of MMA can be found at http://nantucket.plumtv.com/videos/snakes_island.  Most of the arrays recorded garter snakes and ring necked snakes in 2007, although two northern water snakes were found hanging out at the Pout Ponds.  During the summer months, the MMA Natural History Museum on Vestal Street will often have one or two live snakes for the public to view.

The northern water snake (Nerodia sipedon) is a stout snake that can grow to over four feet and is variable in color and pattern. Background color ranges from light gray to dark brown. It is almost always patterned with reddish-brown, brown or black crossbands near the head and alternating back and side blotches farther down the body. The pattern generally becomes less noticeable as the water snake grows larger, and often results in a uniformly dark snake except for the belly which is patterned with black or orange crescents. Some people confuse the northern water snakes for venomous copperheads or cottonmouth snakes, which also prefer water habitats.  Northern water snakes have keeled scales, which mean that each individual scale has a narrow ridge running down its middle. This is an important feature when identifying groups of snakes.  Garter snakes and water snakes have keeled scales, rat snakes have weakly keeled scales, and king snakes and racers have "smooth" scales.  The northern water snake pictured here was almost four feet long, over an inch in diameter, and very dark which indicates that it was an older snake.

Courtship and mating for northern water snakes typically occur in May and June, and females give birth to 20-40 young in August and September. True to their name, water snakes are found in a variety of wet habitats including lakes, ponds, rivers, streams, and wetlands. They are excellent swimmers, both on the surface or submerged, and commonly forage along the water's edge for prey. Fish, frogs, tadpoles, and salamanders make up the bulk of their diet, though they will also take small mammals, birds, insects, crayfish, and other invertebrates.  Water snakes are very common and can often be found on bridge abutments, banks, and under wetland shrubs. When threatened, they rapidly retreat to water.  If cornered, they do not hesitate to strike.  Water snakes can almost always be counted on to bite, defecate, and spray a particularly foul-smelling musk when handled, which are excellent reasons not to try and pick one up.

Generally, 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.  Although the pattern is variable, it usually consists of a narrow stripe down the middle of the back and a broad stripe on each side.  Between the center and each side stripe are two rows of alternating black spots. Background color is usually brown or black, but may be somewhat green or reddish. Stripes may be tan, yellow or orange. A garter snake will occasionally appear more checkered than striped. Garter snakes also have keeled scales.

Garter snakes generally mate after emerging from hibernation in March or April. Females give birth to 12-40 young any time from July through October. Garter snakes can be found in a variety of habitats including pond and stream edges, wetlands, forests, fields, rocky hillsides, and residential areas.  They are often observed as they bask on rocks, wood piles, stone walls, hedges, and swimming pool decks.  Garter snakes are often found in surburban settings and they like to hide in outbuildings, sheds, and wood piles. Although they feed on a variety of small animals, garter snakes' primary prey are earthworms and amphibians. Their saliva appears to be toxic to amphibians and other small animals, and a bite from a large garter snake may produce temporary swelling or a burning rash in some people.  Although garter snakes may or may not bite if handled, most secrete a foul-smelling fluid from anal glands when alarmed.

A boldly patterned and quite beautiful snake, 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.  Similarity of patterns causes some people to confuse it with the copperhead; however, the copperhead lacks any pattern on the head.  Tail rattling may also lead some to mistake milk snakes for rattlesnakes, although the two species look very different. Neither copperheads nor cottonmouths are on Nantucket.

Milk snake mating generally occurs in May, with females depositing 3-24 eggs in June and July.  Eggs are deposited under rocks, boards or other debris, in rotting vegetation, stumps or logs, or small mammal burrows, and usually hatch in August and September. Woodlands, fields and borders of wetlands provide natural habitat for milk snakes.  They are also commonly found around houses, barns and outbuildings.  As mentioned above, milk snakes eat small rodents like mice and they also will eat other snakes, bird eggs, frogs, fish, earthworms, slugs and insects. Although they are not very aggressive, milk snakes will bite and spray musk if handled.

The eastern ribbon snake (Thamnophis sauritus) is a very slender, striped snake, similar in appearance to the garter snake but with a much longer tail. Ribbon snakes are boldly patterned with three yellow stripes on a reddish-brown background.  A distinct dark band separates each side stripe from the belly.  The ribbon snake has keeled scales and a belly that is pale yellow or pale green. Ribbon snakes generally mate in the spring (April-May), after emerging from hibernation, and females give birth to 10-12 young in July or August. The preferred habitats of ribbon snakes are wetlands and the edges of ponds and streams. Amphibians, especially frogs, are their preferred food, although fish and insects are also taken.  Given their preference for wet habitats, ribbon snakes tend to be most active during the spring.  If summer weather dries up their environment they may become dormant until conditions improve.  Ribbon snakes are comfortable both in and out of water and are adept swimmers.  They may be found basking on logs or hummocks and they will escape rapidly into dense cover or open water if threatened.  Ribbon snakes rarely bite if handled, but they do secrete a foul musk from their anal glands when alarmed.

Named for a yellow band around the neck, the ringneck snake (Diadophis punctatus) is relatively easy to identify.  Its back can be slate gray, black, or brown with smooth scales giving it a satin-like appearance. A complete yellow ring just behind the head, along with smooth scales, distinguishes it from red belly or juvenile brown snakes, which are not found on Nantucket. The ringneck’s belly is bright yellow or in rare cases, orange, and may occasionally have a few small black spots. Ringtail mating takes place in spring or fall, with 3-4 eggs (up to ten) laid in June or early July.  Eggs are about 1" long and are deposited together under rocks or other cover, in rotting logs and stumps, mulch piles or small mammal burrows. Hatchlings emerge in August or September. Ringneck snakes prefer moist woodlands as their habitat.  Although salamanders make up the bulk of their diet, ringnecks will also feed on earthworms, insects and, on occasion, fish. As relatively small snakes, they rarely bask in the open and are generally found under cover (rocks, logs, boards, debris) during the day. Ringnecks are typically nocturnal and they are most active in spring and fall and are rarely seen during summer. Ringneck snakes rarely bite, but may release a foul musk when handled. During the summer of 2007, ringnecked snakes were observed at Squam Farm.

Unpatterned and green above, white to pale yellow below, the smooth green snake (Opheodrys vernalis) is difficult to confuse with any other snake in Massachusetts.  Young snakes are dark olive or blue-gray.  The smooth green snake has scales that are not keeled.  Green snakes emerge in April or May and mate in the late spring or summer. Eggs are laid from June to September, usually in two clutches of 4-6 eggs. Females are thought to incubate the eggs inside their bodies before depositing them in rodent burrows, sawdust piles, mounds of rotting vegetation or rotting logs. As a result, the eggs hatch 4-23 days after they are laid, a short period of time relative to other snakes. Fields, wet meadows, bogs, marsh edges and open woodlands provide the kind of concealment cover required by these small snakes. NBI research scientist Scott Smyers reported finding four green snakes at Wyer’s Point on Coatue in 2007 and in the 1976 book This Broken Archipelago Cape Cod and the Islands, Amphibians and Reptiles by James D. Lazell, Jr., green snakes were noted as common on Coatue.  Active during the day, green snakes feed on a variety of arthropods (crickets, grasshoppers, caterpillars, beetles, spiders, centipedes and millipedes). Green snakes rarely bite when handled and when they do, rarely break the skin. If handled roughly enough they will, like other snakes, exude a foul substance from their anal glands.

Although it may be scary to think we are sharing our island with snakes, it is important to remember the role snakes play in the environment and the benefits we gain from them.  Not only do snakes benefit humans by controlling rodent populations, but snake venom has been used to treat various diseases, including cancer, heart disease, and hemophilia.  Unfortunately, some 200 species of snakes are considered threatened or endangered, the biggest threat being habitat loss resulting from human activities.  So the next time you are walking in Squam Farm or the Coskata Woods, keep on the lookout for these beautiful creatures who share our island home.

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