THURSDAY, 21 APRIL 2022
Snakes are a group of reptiles often perceived as scary or creepy. While some species have justifiably earned this reputation, in most cases the true threat posed is negligible. Snakes possess a uniform, recognisable body plan — long, with no limbs — yet there is massive interspecies variation in terms of appearance, habitat, and diet. This variation exists because snakes have adapted to fill niches in many different ecosystems. Snakes therefore represent a fascinating example of the power of adaptation, the process by which evolution shapes animals to best exploit their environment.Where do snakes live?
Snakes are ectothermic, meaning they rely on external heat to regulate their body temperature. This differs from mammals and birds, which can regulate their temperature with heat produced internally. Instead, snakes regulate their body temperature through behavioural mechanisms, such as basking in the sun. Maintaining body temperature in this way is vital for snakes’ survival, as this enables them to digest prey and to move rapidly to escape from predators. The importance of temperature means the majority of snake diversity is present in the tropics. However, this does not mean that snakes are absent from cold climates, and in fact snakes are present on every continent except Antarctica. For example, the vipers (a group that includes rattlesnakes) are surprisingly tolerant of cold temperatures. The European adder, Britain’s only venomous snake, is one such viper that has made its way up north. Vipers are able to cope with cold winter temperatures through a process known as brumation. This is a form of reptilian hibernation, in which the animal enters a dormant state with a relatively low metabolism, saving its energy for when the temperature rises again. This allows snakes to live in geographic areas that experience seasonal shifts in temperature.
What does a snake look like?
Snakes exhibit a wide diversity in size. At over eight and a half metres, the reticulated python is the longest snake in the world, and the heaviest is the green anaconda, clocking in at up to 250 kg. These heavyweights of the snake world are most well recognised due to their prevalence in popular media. But snakes can also be extremely small: the world’s smallest snake is a tiny threadsnake from Barbados, measuring only 10 cm. This snake belongs to a group known as the worm snakes that spend most of their life underground, where they eat the larvae of insects such as ants and termites.
Colour is another feature in which snakes display incredible variation. Most snakes are camouflaged simply by being the same colour as their preferred environment. This is pretty common throughout the animal kingdom as a useful method to avoid detection by prey or predators. However, there are some snakes that buck this trend. The distinctive red, black, and yellow colouration of the coral snakes is instantly recognisable: this kind of bright warning colouration is called aposematism. Common predators of snakes such as birds or primates learn that these bright colours mean danger and avoid the animals that display them. In the case of coral snakes, the danger is a neurotoxic venom, which paralyses the breathing muscles and eventually causes suffocation. Warning colouration means that these snakes don’t need to waste their precious venom (which is energetically costly to produce) on a predator, and can instead save it for small reptiles — their preferred prey.
However, not every brightly coloured snake is dangerous. Some snakes have adapted to take advantage of the fact that aposematism is a common deterrence tactic. Afterall, it’s beneficial to be avoided by predators but energetically expensive to produce venom. So why not just look like a venomous snake? This is precisely what several species of snake have adapted to do — a tactic called Batesian mimicry. The kingsnakes exhibit the same brightly coloured red, black, and yellow striped patterns of coral snakes, but a bite from them would do no more harm than drawing a bit of blood. These snakes live in the same areas as the coral snakes, so predators will avoid them, thinking that they are a venomous coral snake.
How do snakes behave?
Snakes also show a remarkable amount of behavioural variation across their many species.
Like most animals, reproduction for snakes usually involves a male and a female. However, the Brahminy blindsnake, or flowerpot snake, is a small worm snake (the same family as the smallest snake) and is the only known snake that reproduces solely through a process called parthenogenesis. Parthenogenesis, also known as ‘virgin birth’, is where a female animal can reproduce without the presence of a male. This occurs in many snakes and lizards, including the fearsome Komodo dragon. The flowerpot snake takes this one step further and has evolved to reproduce only in this way. This means the Brahminy blindsnake is clonal, with females able to start colonies whenever they want.
We also see remarkable variation in diet. While most snakes eat other vertebrates (fish, mammals, birds, reptiles, or amphibians), several species of mangrove snake have adapted to their unique environment through the evolution of a specialised diet. These snakes are specialised crab-eaters, preferring the soft-shelled, freshly moulted crabs of South East Asia. They are also the only known snakes that rip their prey into smaller pieces before eating them, forgoing the typical snake method of swallowing prey whole. This is likely due to the mechanical difficulties of swallowing a crab in one piece.
Finally, although snakes are usually thought of as solitary animals, a recent study of a species of garter snake has challenged this assumption. As a North American species, garter snakes brumate in large aggregations, emerging together in the spring to mate. Observation of wild populations has shown that large aggregations of individuals are common in many different garter snake species. Researchers from Wilfrid Laurier University in Canada investigated this phenomenon further and found that snakes will actively seek each other out in shelters, preferring to form large groups. Additionally, individual snakes associate with one another non-randomly, meaning that they preferentially spend time with the same individuals, even after being disturbed. This type of study shows not only that snakes are more social than we previously thought, but also that they have the ability to recognise and remember each other. This highlights our need to further understand snake sociality and has significant implications for snake conservation.
Snakes are a fascinating case study into the power of evolution, from extremes of body size, climate tolerance, colour, and even behaviour. By learning more about these often misunderstood animals, we stand to gain a better understanding of how adaptation has led to the diversity of life that we see today.
Alexandra Howard is a final-year PhD student in zoology at Trinity Hall College.
