Snakeskin

Snakeskin may either refer to the skin of a live snake, the shed skin of a snake after molting, or to a type of leather that is made from the hide of a dead snake. Snakeskin and scales can have varying patterns and color formations, providing protection via camouflage from predators. The colors and iridescence in these scales are largely determined by the types and amount of chromatophores located in the dermis of the snake skin. The snake's skin and scales are also an important feature to their locomotion, providing protection and minimizing friction when gliding over surfaces.

In a living snake, its skin often deals with various forms of abrasion. To combat rough substrates, snakes have formed specialized and multilayered organizational epidermal structures to provide a safe and efficient sliding locomotion when maneuvering over rough surfaces.

Snakes can be ornately patterned. They can be striped, banded, solid, green, blue, yellow, red, black, orange, brown, spotted, or have a unique pattern all their own. These color schemes can serve many functions, including camouflage, heat absorption or reflection, or may play other, less understood roles. Melanin cells in the skin often overlap and form complex patterns and sheets that are highly recognizable. Sometimes the soft integument of a snake is colored differently than their hard scales. This is often utilized as a method of predator determent.

Coloration of snakes is largely due to pigment cells and their distribution. Some scales have lightly colored centers, which arise from regions with a reduced cuticle. A thinner cuticle indicates that some sensory organ is present. Scales in general are numerous and coat the epidermis, and come in all shapes and colors. They are helpful in identification of snake species. Chromatophores in the dermis yield coloration when light shines through the corneal layer of the epidermis. There are many kinds of chromatophores. Melanophores yield brown pigmentation, and when paired with guanophores, yield grey. When paired with guanophores and lipophores, yellow results. When guanophores and allophores are added to melanophores, red pigment results. Carotenoids also help produce orange and red colors. Dark snakes (dark brown or black in color) appear as such due to melanocytes that are active in the epidermis. When melanin is absent, albino individuals result. Snakes do not possess blue or green pigments, instead these arise from guanophores, which are also called iridocytes. Iridocytes reside in the dermis, and are responsible for the iridescent appearance of many dark-colored snakes. Males and females may show varied coloration, as might hatchlings and adults of the same species.

Snakeskin, or integument, is more than just patterns and scales. Scales and patterning are features of snakeskin, and they are derived from a soft and complex integument. These scale patterns are unique to species, and the scales themselves help in locomoting by providing a friction buffer between the snake and the ground

Reptiles, including snakes, possess extensive keratinization of the epidermis in the form of epidermal scales. A snake's epidermis is composed of four layers. The outer layer of a snake's skin is shed periodically, and is therefore a temporary layer, and is highly keratinized. Beneath the outer layer is the corneal layer (stratum corneum), which is thickened and flexible. Under the corneal layer is intermediary zone (stratum granulosum) and the basal layer (stratum basale), respectively. The dermis of a snake resides beneath the epidermis. The dermis of snakes is generally fibrous in nature, and not very prominent. The dermis houses pigment cells, nerves, and collagen fibers. Nerve fibers extend into the snake epidermis and anchor near scales, generally at the rostral, or head, end of the snake. Specifically, nerves anchor to sensory spines and pits, which are touch and thermal detection organs, respectively. The hypodermis is below the dermis, this layer mainly stores fat.

Snakeskin is composed of a soft, flexible inner layer (alpha-layer), as well as a hard, inflexible outer surface (beta-layer). Snake bodies are in contact with a surface at all times, causing a large amount of friction. As a result, they have to both minimize friction in order to move forward, and generate their own friction in order to create enough propulsion to move. Scale and skin orientation accomplish this, as it has been demonstrated by studies of the nanostructures on their scales. Specifically, the inner alpha-layer contains alpha-keratins which serve as cytoskeletal proteins for a mechanical form of resistance against traction. Additionally, to reduce friction some snakes polish their scales. They secrete an oil from their nasal passage, and then rub the secretion over the scales. This is done at varying intervals depending on the species of snake, sometimes frequently, other times only after shedding or molting. It is thought that scale polishing is used as a method of waterproofing, and it may also play a role in chemical messaging or friction reduction. Lastly, scales and snake skin provide protection in the form of keratin. It has been found, that beta-keratins aid in formation of scales, as the keratin proteins produce a pre-corneous layer of densely packed epidermal scales creating a thick corneous protective layer. Parts of this keratin covering are shaved back to make the snake's scales, the less restricted portion of each scale overlapping the scale behind it. Between scales lies shaved back connecting material, also of keratin, also part of the epidermis. This material allows for the poised glide of the snake over rough stones or gritty sand.

Skin permeability may change seasonally in snakes to help with the problem of drying out. It is known that desert snakes have generally impermeable skins, and that aquatic snakes have a more permeable skin that can sometimes trap water to prevent drying out. Some snakes may change their environment throughout the year, and may subsequently change their skin's permeability as a result. For instance, aquatic snakes may latch on to more water if they are in an environment that is drying out by attracting a layer of water under their scales.