I have been fascinated with cicadas ever since I discovered the weird life cycle of a few species. Rather than a life span of between two and five years, some species (Magicicada) have life spans of a much longer duration. However, almost all of their life is spent at the larval, or nymph, phase. After hatching, the larvae drop to the ground and burrow below its surface; there they remain for either 13 or 17 years, depending on the species, feeding on tree root sap. After the allotted time, they all burst from the ground, shed their final larval skin and emerge as fully mature, sexually reproducing adults in an orgy of synchronicity. I have only ever seen video footge of it but it is as scary as hell. Once they have mated and the eggs have been laid, they die.
Quite why they have such a bizarre life cycle is a matter for some conjecture. It may be that with a long larval stage and the fact that 13 and 17 are prime numbers, only divisible by one and themselves, predators are unable to 'track' them, increasing their own numbers to take advantage of the abundance of cicadas in certain years; the predators quickly becomed sated by the number of cicadas emerging simultaneously and the vast bulk of the insects breed in peace, relatively free from predation. There are other prime numbers lower than 13 or 17, for example 5,7.11, but these may be easier for a predator to track, offering a larger number of instances where the potential for a 'crossover' is greater. For example, if cicadas emerged every five years there would be potential for a bonanza for the predator every 15 years, if the predator was to become locked into a three year cycle of population growth and decline. With the same predator population growth and the cicada on a 17 year cycle, opportunities to synchronise would only happen every 51 years. Whether Mother Nature had indeed been so clever, we shall probably never know for certain but such synchronous 'super-abundance' is quite common as a smart move to foil predators; good tricks once they are discovered are too valuable not to be shared by as many species as possible.
Species of coral release their eggs and sperm simultaneously over an entire reef, although how they manage that trick without even a semblance of a brain is anybody's guess. Horseshoe crabs do something similar, marching up the selfsame beach at the selfsame time as do turtles when they lay their eggs. It is a well worn adage in the kingdom of Animalia; there is safety in numbers and the greater the number, the greater the safety. It is why fish shoal, why birds flock, why ruminants herd, why people band together in communities despite the fact that the greater the number in one place, the more finite is the food resource or mating opportunity for the single individual. However, as my granny always said: "Don't knock it if it works!" She also said: "Don't make love at the garden gate 'cos love may be blind but the neighbours ain't." I never listened to that one either. (Ah, those days of youthful innocence, when you would snog at the gate, rather than on the porch for fear of alerting or waking the 'dreaded bugblatter beast of Thrall' - her mother. We used to get quite an audience of pre-pubescent young girls peering out of first floor bedroom windows. Taking notes?)
It is always difficult to write about wildlife, be they insects, fish, reptiles, birds, monotremes, marsupials, mammals. Bacteria, protozoa, jellyfish (almost but not quite), plants, fungi are easy. Nobody gives it a second's thought that there might actually be intent, a purpose to their behavious in any real sense in the way that we understand the word 'purpose'. However, as soon as a definable body plan becomes apparent, we cannot help but take 'an intentional stance' however we might resist it. We even seek the purpose in a blind algorithm based on chance; evolution by natural selection. However many times Dawkins, Gould, Horner, Bakker, Attenborough et al tell us that we should distance ourselves somewhat, take the scientific approach, still we, and they writing for us, make the same basic error time and time again; we just can't help ourselves.
Dinosaurs grew so big to help them conserve heat by reducing the surface area to volume ratio. No they did not, that would imply intent. They by chance got bigger, there was enough food to sustain them, the climate was warmer, they were too big for all but the largest predators, therefore they survived for eons.
Falcons have baffles in the nostrils to disrupt the air flow and so that they do not have their lungs inflating to bursting point when they launch in to a power dive at over 250kph. No, the first falcon who tried that trick without baffles blew him/herself up; the first falcon to try it with baffles did not. He/she was thus able to move faster through the air and probably caught more prey as a result. Survival.
The cheetah has non-retractable claws unlike other cats which give it greater traction across the savannah, like a sprinter's spikes. No. For reasons best known to God, a freak was born who could not retract his/her claws. He/she found that his/her hunting success went up from 1 in 15 hunts successful to 1 in 10, therefore more cubs raised and fitter animals all round for those that inherit non-retractable claws.
The single most important question to human beings is 'why?' It is why we spend so much time, money and energy on theorising and 'proving' that theorising. When it come to life, it is really difficult to do that. You can no more account for the disappearence of archeopteryx from the fossil record than you can find God in a grain of sand. If an animal, in the broadest sense, is alive now then it is at least passibly suited to its environment. If that situation should change then perhaps the animal will become extinct, or it may profilerate in numbers unheard of, or it will remain, just as it is.
In many ways, popular writing on Life on Earth is merely so many 'Just So Stories', tell the stories that have some 'explanation' and sweep everything else under the carpet of 'neutral mutation'. Of course, there may be all kinds of pressures on mutations but the mutations have to happen first, quite randomly or maybe not so randomly, before evolution, the environment can test them and prove them fit or otherwise. It is this point that I think 'populist' writers about science do not emphasis enough.
There is nice animated gif of a cicada shedding its old skin which I have nicked from Wikipedia for convenience. The usual creative commons blurb applies.
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