They lie, manipulate and lead us astray. They can also perfectly imitate others. Butterflies, snakes, potoos and cuckoos are pretty good at conning.
I’ve been completely fooled and brilliantly manipulated; I’m jumping with joy on slippery stones. No one has ever deceived me and thumbed my nose in such style. There are still six to seven kilometres on foot before I reach the Las Cruces biological research station. I might get drenched, but the tropical air is already dense with humidity. On the neighbouring bank of the Java River Valley, white clouds are beginning to buzz and swell, climbing over the mountain ridge from the nearby valley and the settlement of San Vito below. A Costa Rican downpour is approaching fast. I shrug and count on my fingers like a child, enumerating to myself all the vile and sensual tricks that the jungle played on me today. It’s my first day in Las Cruces, but I already feel like an 18th-century explorer. Let me be clear: in the era of the internet and documentary masterpieces narrated by David Attenborough – as well as automatic photo traps capable of capturing the most discreet and intimate secrets of life – being a biologist has lost some of its pioneering and Romantic appeal. Within the reach of our hands (or computer mouse), we have everything that explorers like Stephen Jay Gould, Alexander von Humboldt and John James Audubon would painstakingly record in words and pictures.
Still, meeting eye to eye with the most honest natural deception, ruffling its stiff fur or peering at it through binoculars are moments of the purest, unbridled naturalists’ joy. As a biologist and an academic, I am naturally convinced about the reality of all these adaptations, characteristics and strategies invented by life to survive. However, at times I find it unbelievable that all of these fascinating species actually exist and live out there somewhere – running, flying and walking, breathing and eating – and that they are not figments of imagination dreamed up by malicious schemers who indulge in creating monsters to fill the pages of natural history handbooks. It is only in the tropical cabinet of curiosities located in the American jungle or hovering in silence over the distant corners of coral lagoons that I sigh with relief, concluding that they are indeed out there after all.
On that muggy July day, the Costa Rican jungle was in the mood for jesting. It began with a green-grey object hanging motionlessly from a fig tree branch extending across a forest path. Juan, my guide to this alien world, noticed this nondescript rough lump long before me. If it had not been for him, I would have walked by unaware of the secret it was hiding. We stopped right before it and Juan prodded me to touch the felt-like thing. Not knowing what to expect, there was something off about the feel of it, matching its unappealing looks. It was rough and sticky, exuding a slightly musky scent. Then, probably under the brush of my hand, it began to move.
It was a brown-throated sloth, casually hanging undetected from a fig tree in the middle of a tropical nowhere. The poor thing must have dozed off there, putting itself incautiously in front of travellers, just within hand’s reach. When touched, the green-grey ball snorted and began to fidget in the unique slo-mo manner typical for sloths. Impossibly steady and measured, it clutched at the branch in an effort to move away from us, unabashed intruders who disturbed its sleep and blissful immobility.
For a moment, I wondered how this sluggish animal could simply forget about everything and hang from a branch over a trail, far from the safety of the thick forest. What would happen if the sloth was spotted by an animal less friendly than me? When I glanced back a while later, the sloth was moving from branch to branch. It then dawned on me how naïve I had been. We could still hear it occasionally rustling the stiff fig leaves, but spying it was a challenge. The sloth stopped being a sloth and looked rather like an invisible green-grey tangle of moss and lichen.
For several more hours, I continued to be deceived and tantalized. Juan must have deemed it a point of honour to turn our walk into a lesson of humility, taught by jungle marvels that would shame my credulous senses. On our way, we encountered leaves and branches that were not what they seemed, butterflies that looked both how I expected them to and not. We even came across ones that appeared ordinary, but then revealed themselves to be something completely different. Somewhere in the foliage there was a weird branch that we miraculously spotted, desperate not to give off any signs that it was in fact not a part of the tree. Its blind eyes turned to us, revealing the most beautiful pair of pupils I had ever seen: snake’s eyes. There was no need to be afraid of it, although it certainly wanted me to be scared. The jungle later charmed us with even more tricks and stratagems. I was browsing in my mind through all the books on evolutionary ecology I knew, trying to find technical terms to describe their lies.
Camouflage, cloaks of invisibility and other minor deceits can be described as forms of mimesis, which is essentially a form of animal communication designed specifically to fool others. The root of this term is the Greek word mimetikos, which denotes imitation or attempting to imitate something else. Mimesis is used by evolutionary ecologists to describe the countless strategies developed by masters of this art to elude, sometimes by literally disappearing from the field of view. At the same time, mimesis can involve appearing in the eyes of onlookers as something complete different. In such cases, however, it is described more precisely as mimicry.
The sloth I met early on my journey exemplified a special kind of mimesis. Due to their slowness and clumsiness, sloths seem to be easy prey for jungle predators. However, owing to their lazy lifestyle and specific texture of fur, sloths easily hide from unwanted eyes so well that even from up close they appear to be a motionless tangle of plants. In a way, sloths almost become what they try to imitate. Their highly porous fur quickly catches humidity in the dense tropical air and becomes covered with layers of greenish algae and liverworts.
On that day in the Costa Rican wonderland, I encountered many animals wearing such cloaks of invisibility. With every step, I would stumble upon insects pretending to be twigs, leaves or irregular tangles of branches. Some of them were stick-insects (such as the Vietnamese walking sticks often found in home terrariums), while others were Orthoptera (such as the well-known crickets). One withered branch turned out to be a surly, stocky bird – a potoo – spotted by Juan in the tree’s lower crown. I am amazed to this day how he managed to spy it, because resting potoos tense up, aligning their body with neighbouring twigs. When motionless, they offer an example of perfect mimesis, as their camouflage is impossible to unmask. The potoo we found long pretended to be the most ordinary branch, just like any other in this part of the world. I was able to call its bluff only when it unguardedly blinked with one of its large, golden-yellow eyes. Otherwise, I would not believe that Juan had noticed it just like that in the tangle of other equally ordinary withered twigs.
As mentioned above, mimesis does not always entail camouflage and indistinctness. One elegant example of bordering between visibility and invisibility is provided by a butterfly that landed on my forearm at the gate to the Las Cruces reservation. The size of two palms, it appeared to be a flake of grey bark until it extended its wide wings and a pair of protruding eyes suddenly emerged. Naturally, it was a deception – a simple trick ensuring that the butterfly can scare off enemies in case they did not fall for the illusion of brown-grey bark. The giant pupils appearing in an instant could potentially terrify any unwelcome company.
Sometimes, however, even partial blending with the background is not the best strategy. In such cases, it seems better to shine with neon colours – especially those that invoke somebody else’s hard-won reputation. In Costa Rica, one must be ready for encounters not only with stately sloths, but also with poisonous monstrosities like bullet ants, bird spiders and coral snakes. The last are deceptively cute and relatively small animals wearing beautifully contrasting colours in black, red and cream strips. They are among the most poisonous reptiles; the toxin they produce works slowly but surely, eventually paralysing the muscles necessary for breathing, thus gradually suffocating the victim. Their bright colours are a reliable means of scaring off others. I realized this when we came across a pacing reptile covered – to our dismay– with highly characteristic red, white and black strips. As it quickly turned out, I was once again duped by mimesis, specifically a form of mimicry used by the American milk snake. Although they are not poisonous, their protective colouration is quite similar to that of coral snakes, the only difference between the species consisting in the proportion between white and black strips. In a mockery of another species’ well-established defences, they partake in its murderous reputation without paying the cost of producing the precious toxin.
This sort of mimicry is widespread. It is called Batesian mimicry, in memory of the British naturalist Henry Walter Bates. We encounter it whenever a harmless organism imitates the appearance of a poisonous or inedible one. In Poland, this kind of mimicry is used by hover flies, which look deceptively similar to the stinging wasps. During my Costa Rican adventure, I met swarms of such insects. Many American butterflies enjoy the protection that this adaptation offers. During the first hour of our journey, Juan correctly recognized one butterfly flying around us as Papilio zagreus, telling me to remember its appearance. Several hours later, I once more saw the characteristic pattern of orange spots on a velvety black background, but this time on the wings of another species. In fact, Papilio zagreus pretends to be the latter butterfly, a poisonous representative of Heliconius, which produce cyanide from pollen.
Heliconius is intriguing in itself, as its strategy differs from the deceitful mimicry identified by Bates. These butterflies work alongside each other, representing Müller-type mimicry, named after the German naturalist Fritz Müller. Instead of stealing the protective colouring carefully developed by others, Heliconius butterflies create complexes of mimicry, with several similarly poisonous species adopting similar looks. The logic of this mimicry is simple: by eliminating sensory overload and simplifying signals, these species make sure that potential enemies quickly learn about this visual warning. Indeed, during my first walk in Las Cruces, we encountered at least three strikingly similar representatives of Heliconius.
It would be unfair to stop here and limit the discussion to the remote Costa Rican province of Puntarenas. The jungle, where something wants to eat you at every step, is an ideal habitat for the evolution of mimesis. The life-saving art of deception is very precious in this context. However, mimicry is not found only among tropical animals. Mimesis and classic mimicry also developed in Europe, where the climate and natural conditions are more moderate. Among the masters of imitation and colour-conning are a species we can all encounter: cuckoos, recognizable at least for their characteristic singing.
We know this much about cuckoos: they are reproductive deceivers, perfidious and heartless mothers who place their eggs in the nests of other species, who naively raise the cuckoo offspring with care. However, should we blame the trusting adoptive parents of Sylviidae and reed warblers, brutally exploited by cuckoos? Certainly not. The latter know what they are doing and make an effort to stop the hosts from rejecting cuckoo eggs. They are able to achieve this thanks to one of the most spectacular forms of imitation-based deception.
The mimesis used by cuckoo mothers consists primarily in laying eggs that look deceptively like the ones of the exploited species. Although cuckoo eggs are typically larger (the birds on which cuckoos parasite are usually small songbirds), their colouration matches that of the host’s. Cuckoo females are genetically predisposed to produce specific colouration, which makes them part of a group of animals that specialize in producing eggs perfectly imitating those of other species.
Although it seems simple and brilliant, this strategy can be dangerous. Differentiation of the cuckoo family into specialist species within such short time (from an evolutionary perspective) could lead to the emergence of numerous smaller sub-species quickly moving away from each other. Some might survive, while others could die out due to genetic isolation from other cuckoos. What keeps this species intact is the male population of cuckoos, who have no preferences regarding the female they want to mate with, not caring at all what colouration a given female can produce. Thoroughly universal, cuckoo males only make sure that the other cuckoo represents the right species, irrespective of the extravagances displayed by individualistic females. The latter can thus remain undisturbed and carry on developing their unique egg colouration imitating the hues and patterns of their hosts. In fact, the rivalry between the deceivers and the deceived never stops, as the former keep on developing better ways of cheating, while the latter continue resisting these manipulative efforts and try to find ways of unmasking such tricks more quickly. And so the struggle continues – an egg war in the case of cuckoos – setting the wheels of evolution in motion and providing avid and excitable naturalists with something they can enthuse over and record in their field notebooks.
Translated from the Polish by Grzegorz Czemiel
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