Rattlesnakes are venomous pit vipers known for their distinctive tail-end structure. Shedding their outer layer of skin, known as ecdysis, is a recurring biological necessity. The timing of when a rattlesnake sheds is highly variable, responding to a combination of internal and external conditions, rather than being a fixed annual event.
The Biological Necessity of Shedding
The outermost layer of a rattlesnake’s skin, called the epidermis, is a tough, non-elastic covering. Since it does not expand as the snake grows, shedding (ecdysis) is primarily required to accommodate an increase in body size. This is particularly frequent and noticeable in younger, rapidly growing individuals.
Ecdysis also serves as a regular maintenance cycle for the snake’s health. Shedding the old skin helps to repair minor wounds or abrasions the snake may have sustained in its environment. A complete shed also functions as a method of pest control, removing external parasites such as mites and ticks that may have attached themselves to the outer layer of scales.
Factors Determining Shedding Frequency
Life Stage
A rattlesnake’s life stage is the primary determinant of shedding frequency. Juvenile rattlesnakes, experiencing rapid growth, shed more frequently, sometimes up to four times annually. Older, mature adult snakes shed less often, typically undergoing ecdysis only once or twice per year.
Environmental Conditions
Environmental conditions regulate the timing of shedding by influencing the snake’s metabolism. Shedding occurs more frequently during warmer months when the snake is active, feeding, and growing. During winter brumation, a period of dormancy, the snake’s metabolism slows significantly, and shedding ceases entirely until warmer temperatures return.
Resources and Physiological Demands
The availability of food and the snake’s overall body condition directly impact its growth rate and shedding frequency. A snake with a successful hunting record and high caloric intake will grow faster and need to shed more often to accommodate the size increase. Shedding patterns may also be coupled to physiological demands, such as mating season in adult males. The process requires a significant investment of metabolic energy, which can limit frequency when resources are scarce.
Observable Stages of Ecdysis
The shedding process begins internally, triggered by hormonal changes that cause a fluid layer to form between the old and new skin layers. The first noticeable sign is that the skin begins to look dull and muted. The snake’s eyes also undergo a change, becoming cloudy or opaque due to the old spectacle, the clear scale covering the eye, separating from the new one.
This period is often referred to as the “in the blue” phase, and it results in temporary visual impairment. Because of this vulnerability, the rattlesnake will often seek out a secluded, protected location and may stop foraging for food until the cloudiness subsides. The preparatory phase can last for several days up to a couple of weeks, depending on the snake and environmental temperatures.
Once the fluid is reabsorbed and the new skin is fully formed underneath, the snake prepares for the final stage of removal. The rattlesnake rubs its snout against a rough surface, such as a rock, log, or coarse bark, to create a tear in the old skin near its head. It then crawls forward, effectively peeling the old layer off inside-out, much like removing a sock. This final removal typically results in the old skin being discarded as one continuous piece, including the eye spectacles.
The Relationship Between Shedding and Rattle Growth
Ecdysis is directly responsible for the growth of the rattle. A new, keratinous segment is added to the base of the rattle every time the snake successfully sheds its skin. This new segment is initially soft, but it quickly dries and hardens once the old skin is sloughed off, interlocking with the segments that came before it.
The newest segment is always located closest to the snake’s body, while the oldest segments are at the very tip of the rattle. Counting segments is an inaccurate way to determine age because the frequency of shedding is highly variable, often occurring multiple times per year when the snake is young. Furthermore, the brittle segments can break off due to wear and tear from moving through rough terrain or during encounters with predators. The number of rattle segments only indicates the number of times the snake has shed since its last break.