“Men it appears would rather believe than know” wrote E.O. Wilson in his seminal book “On human nature”, and this sad truth is evident in many aspects of our life, including, strangely, the world of nature photography. One of my pet peeves has always been the tendency of some editors to rotate pictures of animals that prefer to look at the world with their heads pointing down, so that in the modified photo their posture appears more similar to ours. Somehow, this fakery to make animals more anthropomorphic has always been considered pretty innocuous and, to my dismay and outrage, on many occasions my photos were modified in this way without consultation.
Why is it that such a blatant distortion of the natural world is considered acceptable? If I Photoshopped a giant panda so that its fur is pink, everybody would be up in arms, but if a photo shows a praying mantis molting with its head pointing up then all is fine and good. The first is conceivably possible with a simple mutation, the second would require turning off the gravitational forces of the planet in order to happen.
And yet, we prefer to go along the easier path of believing that all animals have the same preference to hold their heads high, and that this is somehow the “right” way. But for many organisms, especially those that make a living by being sit-and-wait predators, keeping the head pointing down makes far more sense.
First, hanging from a branch, as opposed to standing on it, is much more efficient energetically. All you need is sharp claws to grasp the branch, and gravitation will make sure that these are firmly embedded in the bark, and no muscle power is required to keep the animal from falling. If you look at animals that spend their lives in this way – praying mantids, sloths, bats – you will notice that their leg muscles are severely reduced, and some can barely walk if forced to stand with the head pointing up. The energy that would otherwise go into legs can be diverted into other parts of the body: the powerful raptorial arms of the mantis or wings of the bat. (Sloths are a special case – the fact that they don’t need to walk allows them to grow really large, considering how nutritionally poor their food is. Any walking mammal their size would quickly starve if its diet were as meager as that of the sloth. )
Second, by hanging upside down, sit-and-wait predators are better able to blend in among the vegetation, which also tends to droop towards the ground. Relatively few arboreal sit-and-wait predators walk on branches, rather than hanging from them (chameleons are one of the examples.)
And finally, molting. A molt is a very special time in the life of an arthropod, a moment that we, mammals, cannot possibly identify with. It is a moment of ultimate weakness and vulnerability, and the faster you can go through it the better. So why don’t most insects use their legs to quickly crawl out of their old exoskeleton? The reason is that while the muscles of a molting insect or spider are fully functional, their points of attachment are not. Our muscles rest on the always rigid internal skeleton, and when we flex a muscle we don’t run the risk of bending a bone. But a molting insect does, because its exoskeleton, which contains points of attachment of all muscles, is at that point very soft. It can be easily distorted if any muscle is engaged while chitin, the polysaccharide that makes up the bulk of the skeleton, is still hardening. If an insect bends a leg during the molt, its exoskeleton may solidify in the bent position, making it unusable in the future. For this reason most terrestrial arthropods prefer to molt by slowly slipping out of their old, smaller exoskeleton, using the gravitational forces of Earth to their advantage.
And so, next time you see a photo of a butterfly emerging from the chrysalis towards the sun, or a praying mantis standing on its stick-like legs and holding a giant grasshopper towards the sky, don’t believe it. The truth may be a little more difficult to grasp, but it will give you a more beautiful picture of the world.