Night and day


Text and photographs Pat McKrill

‘I feel it in my fingers, I feel it in my toes………’
The opening words from the song ‘Love is all around us’, would be appropriate for my limbless friends, if it weren’t for the fact that they have neither fingers nor toes. But with their clinical diagnostic, and habitat adaptive equipment inherited through evolutionary changes over millions of years, they won’t need them. They’ve been designed to ‘feel’ a great deal more than humans will, after all, they’re predators.

I’ve been asked to offer my perspective, as to why I think these skills, or features were developed in some creatures – in this case, some snakes – and not all of them. My comments represent my interpretations of what I’ve read, seen and experienced in my life, there’ll surely be contrary views and I’d welcome yours. Why didn’t they all evolve in the same manner? The features are those that seem to be more enhanced in some species, due it seems, to the similarly evolutionary changes that were taking place in their ever developing environment. We’re told that these changes took place over millions of years, long before the relatively recent – in terms of our history – arrival of humans on the planet.

Hom sap. No fear of predation. Enjoying the braai.

Causus rhombeatus. Night adder ‘tasting’ for frogs.

Humans are adapting

Humans have not experienced too many radical evolutionary changes in their time on this earth. We haven’t been here long enough to really notice major changes. In those relatively recent days about 200,000 years ago, when man emerged from his cave, the standard hunting, killing, eating type of behaviour was probably much easier to accomplish in the daylight rather than in the dark, so why change? There seemed to be no further reason to evolve, other than perhaps to lose some body hair, stand up straight, get dressed and speak properly.
Since then, little has evolved within the human body. I can’t be the only one who’d assumed that when our ancestors arrived, they could walk on two feet without falling over, and as such, we were designed to work in the daylight only, and sleep at night. Evolution was not in my vocabulary.
Perhaps one evening, whilst mindlessly wandering around, swatting away irritating flying insects with internally-generated lighting in their bodies, and occasionally thinking about moving on in life, someone asked – ‘why can’t we do what they do’? And they decided to investigate and copy the mechanisms. Then they investigated the heat-detecting ability they’d noticed in some snakes (e.g. Python). The end results were not what could be termed ‘evolutionary developments’ in our history, they were simply human-adapted replications of things they’d noticed, that already existed in animals. And so we’ve moved on…

Python natalensis. Southern African Python. Infra-red sensors at the ready.

Animal behaviour is an adaptive response

The more noticeable changes we see amongst some animals in terms of their behaviour, searching for new habitats or food sources etc. cannot be termed ‘evolutionary’. A habitat change because of say, industrial development, or the burgeoning growth of bird-friendly vegetation on a rapidly expanding ‘Eco Estate’, is an adaptation. Both situations would very likely experience consequential arrivals of new ‘tenants’ who’ve been attracted to the new environment, and who in turn, would have undoubtedly been seen as attractive food sources for other, observant predatorial animals.
In the first example, food items such as rats and mice would soon head for their new food magnets; human waste, compost, plant matter etc. in the associated industrial waste tips, a move which would be closely followed by a consequential migration into those areas, of already suitably evolved predators, like snakes. If the climatic conditions suited their habitat choice, many of our most common and opportunistic predators would be drawn to the area; the Black Mambas (Dendroaspis polylepis) and the Brown House snakes (Lamprophis capensis) would certainly be amongst those joining the migration. This type of change in faunal habituation is commonly seen in towns and cities where the human populations grow rapidly. The predators follow the food.

Lamprophis capensis. Adult Brown house snake looking for rodents.

Juvenile Brown house snake. Lizard lover.

Evolutionary change is driven by necessity

The snakes would have been drawn to this food bonanza, not by voice messages or the distant sight of rats and mice running around. Snakes can’t speak, have no ears to hear with, and don’t all have great eyesight, but they do have a powerful scent detection organ (Jacobson’s organ) in their head, which has evolved over millions of years – giving them the ability to not only silently ‘communicate’ with others of their species, using their own signature scents, but also detect and identify surface-based and air-borne scents of other creatures and locations over long distances.

In the Eco Estate scenario, many bird species will find the vegetation in the Estate forests suited to their habitat choice, making it an obvious drawcard for them. Some of the consequential predators who prey upon them, might be more specialised feeders, such as the arboreal (tree living) Boomslang (Dispholidus typhus) and the Egg-eaters (Dasypeltis spp). In addition to the snakes’ scent identification skills mentioned earlier, which would be that which had alerted them to the new food sources, other snakes would have adopted over millions of years of evolution, other innovative means designed to meet new requirements. A good example of this would be the skull structures designed to enable them to swallow food items considerably larger than their head size might suggest possible. Egg-eaters can engulf a large egg, ‘saw’ through the shell with their specifically modified backbone, compress the eggshell inside the mouth, swallow the contents, and regurgitate the empty shell.

Having been involved with in-field snake awareness training on rapidly developing tree-nut plantations, I’ve become aware of how quickly predatory snakes – in this case, Boomslang – can be drawn to new areas and food sources where they’ve not been recorded previously, by the consequentially growing bird populations. Again I add, this particular migration by others to a new food source area would be an adaptation, not an evolutionary change. Any wild animal drawn to a new and attractive food source, will make every effort to adapt to that situation as quickly as possible.

Boomslang male. Arboreal but adapts well to scrub if the food is there.

Southern Brown egg eater seeking a new nest.

Egg eater about to crush the egg.

All that remains of the emptied egg.

In this article, I’ve merely touched the tip of the iceberg when mentioning radical and long-term evolutionary changes in the make-up of the affected creatures. Loss of appendages such as limbs and eyelids, the development of chemical signal receptors and temperature-sensitive pits in Puff adders (Bitis arietans) etc. are just some of the many changes. Consider the changes in the eye area, where snakes have evolved with the ability to have a more specific sight application – some species are better adapted to daylight operation, some for night.

When assessing the i.d. (birders might say, the ’jizz’) of a snake in a tree, or crossing the road, I always try to look at the eyes of the snake. If it’s got elliptical pupils, I’d go for nocturnal. These pupils can dilate at night in order to allow more light into the eye, and these snakes are often tree dwellers who climb in and out of dark holes in the trees, looking for food. If the pupil is permanently large and fills the eye, I’d guess diurnal – the daytime hunter. The pupil has specifically evolved in order to enhance the eyesight of the snake, relative to the way it lives/hunts etc.

Bitis arietans. Puff adder with numerous built in modifications.

Structural changes can be determined by habitat

Body structures also evolved in some species to allow for specific habitat choices. The Spotted Rock snake (Lamprophis guttatus) is an example, where the head is markedly flatter than that of its close cousins, the Brown and the Olive house snakes, allowing it to live and hunt in amongst the narrow rock crevices where it occurs, and the venomous Stiletto snake (Atractaspis spp.) which is a fairly common underground – fossorial – dweller, has a denture modification that allows it to strike or stab backwards or sideways in the narrow underground tunnels, where it cannot open its mouth to embed the fangs.

Lamprophis guttatus. Spotted rock snake with its modified body shape and pupils.

Lamprophis inornatus. Olive house snake. Bulky head and neck. Diurnal.

For snakes to survive through the changing millennia, they’d have to evolve and adapt to new conditions: those that directly affected them, not all snakes. It’s also appropriate to mention that the early ancestors of our snakes, such as some of our ‘blind snakes’ e.g. family Typhlopidae dating back some 130 million years plus, have seemingly remained unchanged – or had the decision made for them – and stayed as they were, deeper down in the darker, muddier parts of the earth. They retained their requisite, possibly limited in our minds, assets – small eyes, small mouths, no real teeth, and not so muscular structures, but all of which dealt quite adequately with their existing food sources such as ant eggs and larvae. But the later arrivals e.g. family Colubridae, actually came above ground, out of the dark. In their new world, there was a lot more action, 24/7.

So perhaps it makes sense to say that for those more recently arrived species that had evolved, no matter what family, the changes were probably intended to help them get accustomed to daylight activities, thus becoming diurnal, rather than their specifically nocturnal predecessors. Was there perhaps more food available during the day?

Philothamnus natalensis. Natal Green snake expanding to absorb external heat.

Philothamnus semivariegatus. Spotted bush snake. A pocket rocket.

From what we understand from archaeological findings and records, it would appear that man was unlikely to have been created as a hunter-killer like many of the other creatures on this earth. Yes, in the beginning, he ran around clubbing things to death and then eating them, but most of the weaponry used by him was essentially created and/or designed and adapted by him to accomplish the necessary task.

As with most creatures, man aside, later models have evolved over the millennia, and will continue to do so, coming up with upgraded specifications and adaptations. The creatures (and plants it must be added) that have markedly adapted over time were all hunters in one way or another, not supermarket shoppers, and the amazing evolutionary changes they’ve acquired over their millions of years on the same earth, have come about as their respective needs to attract and/or see others, whether by day (diurnal) or at night (nocturnal) arose.

As I’ve said before in my articles, snakes were put on this earth for a specific reason, which was to act as another of those extremely necessary biological controls designed to keep our environment healthy. They need to live healthy lives in their chosen domain, procure by various means readily available food, and ensure continuity.

Now, about the fingers and toes……..

As far as the snakes were concerned, most of them had limbs of some sort in their earlier form, gradually losing them as they evolved, although there are still some of those, our same python – the one with the IR camera – in which hind limbs remain vestigial in the form of claws to this day. We are told that the male python uses these during the mating process, as a form of assistance in the “come along” phase of the courtship. An evolutionary process in snakes has allowed for the development of alternative sensory devices to assist with the ‘touchy – feely’ aspect of their makeup, scientists are discovering through research, just how finite and sensitive these devices are. The snakes no longer need to physically or visibly reach out and touch anymore.

Despite their negative, unwarranted reputations, snakes do an incredible job of remaining hidden from view as much as possible. We might consider ourselves to be well aware of all that goes on about us, the naturally accepted predation that takes place amongst other animals, insects and everything else in the wild, yet despite their constantly overplayed and vicarious exposure on social media platforms, we’re blissfully unaware of snakes!

Which surely confirms that they’ve not only evolving – they’re also adapting.

Author photo: Pat McKrill

About the author

Pat was born in the UK, educated and brought up in Rhodesia/Zimbabwe, and came to South Africa in 1983. He developed an early interest in the study of the behavioural aspects of insects and animals, rather than the deeper scientific side, and he’s worked with snakes for most of his life. Pat conducts educational walks and talks throughout SA and into neighbouring countries where snakes are grossly misunderstood and needlessly killed. He writes articles for a number of publications, and has written the book ‘Getting to Know the Neighbours’, which is all about understanding snake behaviour and is aimed at teaching others how to come to terms with them.

Pat can be contacted at: