You can tell a lot about a snake just by looking at its eyes. Snakes that burrow underground usually have relatively small eyes compared to those that live above ground. The size of the eye and the shape of the pupil can often tell you if the snake is diurnal or nocturnal – typically diurnal snakes have comparatively small eyes with round pupils and nocturnal snakes have larger eyes with elliptical pupils. Both of these characteristics have to do with maximizing or minimizing the amount of light that enters the eyes. The larger the eye, the more light it can gather. The reason for the difference in pupil shape is that round pupils can close very tightly, to a pinpoint opening, shutting out bright sunlight very effectively. Elliptical pupils can open wider than round pupils, and consequently collect more light. (Photo is of a Common Gartersnake.)
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In this photograph taken by Tom Nevins, a Common Gartersnake is swallowing prey — a Gray Treefrog — that is much larger than the snake’s mouth. It can do this because of the structure of its jaws. The quadrate bone, which attaches the upper and lower mandibles, is not rigidly attached. Rather, it pivots, allowing vertical and horizontal rotation of the jaw. In addition, the two pieces of the lower jaw (left and right) are connected in the front of the jaw by an elastic ligament, allowing each side of the lower jaw to move independently. Due to these adaptations, a snake can consume large prey by basically walking over it with its jaws.
When a turtle moves its head, its eye moves to compensate, so that its eye remains in the same position – parallel to the horizon or pond surface — no matter what position the turtle’s head is in. This type of eye stabilization is called vestibulo-ocular reflex (VOR). Humans have a very similar reflex, but it’s easier to detect on a Painted Turtle (pictured) because of its dark eye line. A turtle’s eye structure is stabilized to the horizon, which makes sense, as turtles spend their life close to the ground and/or the pond surface, and this reflex enables it to align its vision horizontally in order to find food, a mate and predators.
In May, at the very same time that adult painted turtles are laying their eggs, some of last year’s young turtles are migrating from their nest site to ponds or rivers. Painted turtle eggs actually hatch in late summer, with the young turtles remaining inside the nest cavity for varying amounts of time. Here in New England, in the northern part of their range, they often overwinter in their nest and emerge the following spring.
Hibernation has come to an end for painted turtles in central Vermont, or at least for the early risers. Painted turtles actually became active a while ago, beneath the ice before ponds were completely thawed. Once some of the ice melts, they are quick to climb up and bask in the sun on any available floating log or rock, or even on the melting edge of the ice. Having spent the winter in the mud at the bottom of the pond at the rather brisk temperature of 39 degrees F. (at 39 degrees F. water achieves its greatest density and sinks to the bottom of ponds, which is where the turtles are), painted turtles are more than ready to get warm. Like black bears, painted turtles find March and April the most challenging months of the year. More of them die now than at any other time, due primarily to a shortage of food.
This is the time of year when snakes take advantage of sunny, mild days by basking in the sun and warming their bodies. It’s possible to come across basking Common Gartersnakes as late as November, as they are more cold tolerant than many species of snakes. All too soon, however, they will be retreating into their hibernacula (hibernation site), where they are protected from severe cold (being ectothermic, snakes cannot control their body temperature). To further protect them, a high level of glucose acts as antifreeze in snakes. The ideal hibernaculum not only serves as a temperature buffer, but also conceals its occupant from potential predators, permits gas exchange, and prevents excessive desiccation. Rock crevices, abandoned woodchuck burrows, rotting tree stumps and old foundations are favorite hibernacula for snakes and other hibernating animals. Gartersnakes typically overwinter in groups, and some even share their hibernacula with other species of snakes, including Smooth Greensnakes, Ring-necked Snakes and Red-bellied Snakes.
Northern Watersnakes can be found in rivers, ponds and bogs throughout New England, except for northern Vermont, New Hampshire and Maine. They spend time foraging both day and night for fish (61% of diet), frogs and toads (21%), salamanders (12%) as well as insects and crayfish at the water’s edge. (Snake jaws can separate at both the front and back, allowing them to eat impossibly large prey , such as the catfish in Chris Crowley’s photograph.) They also spend a great deal of time basking on rocks and overhanging branches. Northern Watersnakes can be formidable looking – they can grow over four feet long – but while they can be aggressive if threatened, they are not poisonous. Watersnakes give birth to up to 70 (typically 20-40) live young between August and early October.
Every fall, roughly 3 months after they’re laid, snapping turtle eggs hatch. The hatchlings’ gender is determined by the temperature at which they were incubated during the summer. In some locations, they emerge from the nest in hours or days, and in others they remain in the nest through the winter. When they emerge above ground, the hatchlings often do so within a few hours of each other. Somehow (questions remain as to exactly how) they navigate to the nearest body of water, which can be up to a quarter of a mile away, and once there, seek shallow water . Look for young hatchlings in small brooks near ponds that are known to have adult snappers. (White object is part of the egg shell that surfaced with this hatchling.)
You can often tell whether a snake is active in the day (diurnal) or during the night (nocturnal) by looking at its eyes. Diurnal snakes, such as the pictured Common Gartersnake, typically have round pupils and moderate-sized eyes. Many nocturnal snakes have large eyes and many also have vertical, elliptical pupils. A round pupil is able to close tightly to a pinpoint opening, allowing a minimum amount of light to enter the eye on very bright days. In contrast, a vertical pupil can open wider than a round pupil to allow more light to enter the eye, a useful adaptation for night vision.
It’s pretty difficult to determine the sex of a Painted Turtle unless you’re extremely close to it, and they are so wary when basking that it takes some maneuvering to get a bird’s eye view of one. If you should be so lucky as to approach a Painted Turtle without having it slip into the water long before you get near it, take a look at the nails, or claws, on its front feet. Males have long claws, female short. The male uses his long claws to stroke the female’s head and neck during courtship, as well as to hold on to the female’s shell when they mate. When trying to determine the gender of a Painted Turtle, it helps when you find the two sexes together, as you can easily compare the relative length of their claws. In the photograph, the male Painted Turtle is on the left, female on the right.
Many snakes, including this Common Gartersnake, use smell to track their prey. In the roof of a snake’s mouth are two openings, called the vomeronasal organ, also known as Jacobson’s organ. Snakes smell by sticking their forked tongue in the air, keeping it constantly moving while they collect particles (mostly pheromones) on it from the ground, air and water. Next they pull their tongue back into their mouth and insert it into their Jacobson’s organ (one fork in each opening). Then the particles are analyzed and the snake determines whether prey or a predator is in the vicinity.
A hole 4” – 5” deep surrounded by scattered empty, dried up eggshells is a telltale sign of turtle nest predation. A painted turtle (judging from the size, depth and location of the nest) dug a hole in the bank of a beaver pond last summer and proceeded to lay roughly a dozen or more eggs in it. After covering the eggs with soil, the turtle returned to her pond. The eggs hatched in August or September. Sometimes young turtles immediately climb up through the earth and emerge above ground, but occasionally, this far north, they overwinter in their underground nest and emerge in the spring. A raccoon, fox or skunk discovered this painted turtle nest early this spring (the digging was fresh) and one can only hope that by the time the nest was raided, the young had already exited and headed for the nearby pond. Research has found that a very small percentage of turtle nests avoid detection by a predator.
After spending several months hibernating in the mud at the bottom of ponds, painted turtles are out, basking in the sun. Because they are ectothermic, or cold-blooded, they are the same temperature as the air around them. In order to warm up and also to properly digest their food, painted turtles bask in the sun, and there is great competition for safe basking locations, such as rocks and floating logs. When these ideal basking sites are limited, the turtles will pile up one on top of the other, staying that way until the bottom turtle gets good and tired of supporting the turtles on top of it, and wobbles enough to make the turtle tower tumble.
12-8-10 Common Gartersnake
The Common Gartersnake (Thamnophis sirtalis) is New England’s most common and widespread snake. It’s not unusual to find one that has been run over on the road, but rarely have I found a carcass of one in the woods, especially this late in the year. Gartersnakes usually are hibernating (often in groups) in rock crevices, rotting logs or holes dug by mammals by October or so. The warmer-than-usual fall certainly allowed for extended basking in the sun and the ability to find active earthworms later in the season. If you look closely you may see that this gartersnake has a blue tinge where it’s normally a greenish color. Yellow and blue pigments in a snake’s skin fuse to produce the green color in living snakes. After death, the yellow pigment breaks down very quickly, whereas the blue pigment is more stable and remains much longer. Gartersnakes that have been dead for a while can have bright blue dorsal and lateral stripes.
Most species of snakes lay eggs (oviparous), but some give birth to live young (viviparous), including the common gartersnake (Thamnophis sirtalis). Gartersnakes are born at this time of year, and are on their own from the moment of birth. The greatest number of gartersnakes to be born in a single litter is 98, but 14 – 40 is more typical. The common gartersnake in the accompanying photograph is a newborn, measuring 6 inches in length.