There are over 4,000 species of snakes across the globe (Uetz, 2022). They vary greatly in shapes, sizes, patterns, colors, and adaptations, making them one of the most diverse groups of animals. Snakes are characterized by having limbless elongated bodies that are covered with scales (Lillywhite, 2014). The two main types of snake scales are smooth and keeled. But there are species, like the file snakes, that have tuberculate (granular) scales as well (O’Shea, 2018). A unique characteristic that defines snakes from other reptiles is that their skin goes through shedding cycles wherein their whole-body exhibits skin shedding. Snakes have a forked tongue but lack external ears or eyelids. Most snake species have modified jaws that enable them to capture and swallow large prey whole (Lillywhite, 2014). While there are harmless snake species, there are also many species that are venomous. The venom is primarily used for prey capture and digestion, apart from spitting cobras who also use venom defensively. However, not all snake venom is the same. There are various types of venom including: neurotoxic, hemotoxic, myotoxic, and cytotoxic venom (O’Shea, 2018).
The evolution of snakes has been a debatable topic in that there are two theories pertaining to their origin. One theory proposes that snakes evolved in a marine setting, and another suggests a terrestrial origin, with the latter theory being more widely accepted. Snakes are part of the class Reptilia and fall under the order Squamata. All snakes are also classified in the suborder Ophidia or Serpentes (Lillywhite 2014; O’Shea, 2018). While some snake lineages only contain a few species, there are other lineages that have hundreds of species. Consequently, snakes have adapted to become successful and marvelously diverse reptiles.
The infraorder Scolecophidia consists of thread snakes, worm snakes, and blind snakes. Blind snakes are non venomous but can release a strong odor when alarmed (Lillywhite, 2014). The brahminy blind snake (Indotyphlops braminus), native to India but found worldwide, is the only known parthenogenetic snake species. Parthenogenesis reproduction occurs when a female’s eggs develop without the fertilization by sperm. Consequently, there are no males known for this species. This infraorder also contains the Barbados thread snake (Tetracheilostoma carlae), which is the world’s smallest snake species with a maximum length of ~10 cm (Lillywhite, 2014; O’Shea, 2018).
Boas and pythons belong to the superfamilies Booidea and Pythonoidea respectively and they include the world’s largest snake species. The reticulated python (Malayopython reticulatus), from Southeast Asia, is the world’s longest snake species growing up to ~10 m in length. The green anaconda (Eunectes murinus), from South America, is the world’s heaviest snake with a maximum weight recorded at over 100 kg. Boas and pythons use constriction to kill their prey and feed primarily on endothermic (warm-blooded) species and have adapted the ability to hunt in the dark. This is possible due to their facial heat-sensitive pits which allow them to detect the body heat of prey (Lillywhite, 2014; O’Shea, 2018).
The family Colubridae contains the more common, familiar, and rear-fanged snake species. For North America these include garter snakes, ribbon snakes, and water snakes. Worldwide species include king snakes, rat snakes, milk snakes, and racers. The astonishing Asian flying snakes are also included in this family. One example is the paradise flying snake (Chrysopelea paradisi). These rear-fanged snakes do not actually fly but they have adapted morphologically to glide. These snakes can expand their ribs and flatten their body to form a concave parachute to leap from trees and glide away to safety when threatened (Lillywhite, 2014; O’Shea, 2018).
Snakes in the family Elapidae are all venomous and include coral snakes, kraits, mambas, cobras, and sea snakes. These snakes all have hollow fixed fangs at the front of the upper jaw. The brightly colored coral snakes are found in the Americas while kraits, mambas, and cobras inhabit Africa and Asia. Cobras are known for their defensive behavior of raising their anterior body and spreading their neck area into a hood. The infamous king cobra (Ophiophagus hannah), which primarily feeds on other snakes, is the world’s longest venomous snake with males reaching ~5 m in length. Some cobra species, like the zebra spitting cobra (Naja nigricincta), have adapted to spit venom when startled, typically aiming for the eyes of their target. Other elapids like sea snakes are entirely marine species and generally inhabit tropical nearshore waters and have high diversity in Oceania. Sea snakes have evolved to their marine environment by having skin adapted to underwater pressure and by having flat paddle shaped tails that aid in swimming. The pelagic sea snake or yellow-bellied sea snake (Hydrophis platurus) is the world’s most widely distributed snake inhabiting the Indian and Pacific oceans (Lillywhite, 2014; O’Shea, 2018).
Vipers and pit vipers belong to the family Viperidae. These species are all venomous with long hinged fangs. Not all but most of these species typically have short bulky bodies, triangular heads with expanded cheeks for venom glands, and keeled scales. Vipers in the genus Bitis are found in Africa and are slow moving snakes but can strike with exceptional speed. The East African gaboon viper (Bitis gabonica) is thought to have the longest fangs reaching ~2 in (5 cm). The color patterns exhibited in this genus, which aid in camouflage, are also astonishing with species like the rhinoceros viper or river jack (Bitis nasicornis) exhibiting geometric patterns with brown, black, blue, and pink colors. The pit viper snakes are in the subfamily Crotalinae and can be found in the Western Hemisphere and Asia. These snakes are named due to these species having heat detecting paired facial pits that assist with prey capture. The most infamous of these pit vipers are rattlesnakes with their distinguishing characteristic of having a “rattle” made of interlocking keratin segments at the tip of the tail. Pit vipers also display marvelous colorations with the Indonesian pit viper or lesser sundas pit viper (Trimeresurus insularis) having green, yellow, and cyan morphotypes (Lillywhite, 2014; O’Shea, 2018).
It is incredible to have such a great diversity of snakes that we share our environments with and we encourage you to learn more about the snake species that live near you.
-Felicia Manning
References
Lillywhite, H.B. (2014) How Snakes Work: Structure, Function and Behavior of the World’s Snakes. Oxford: Oxford University Press.
O’Shea, M. (2018) The Book of Snakes: A Life-Size Guide to Six Hundred Species from Around the World. London: Ivy Press.
Uetz, P. (2022) The Reptile Database. Available at: http://www.reptile-database.org
