Written by Trevor Myburgh, photographs by Vaughan Jessnitz
It is common knowledge that insects are quite intriguing creatures as most are champions of camouflage and deception, capable of changing colour to suit their mood or environment. Some are so well camouflaged that they resemble twigs, thorns, leaves, flowers or bark.
In other cases, a number of harmless species mimic other distasteful or poisonous species by adopting their warning colours such as red, yellow and black. This helps to ward off potential predators.
Bushwise Field Guide students are surrounded by nature during their training and no doubt are lucky to see some of these strategies up close. Since the sheer number of species is so overwhelming, we have chosen but a few examples that will hopefully captivate you.
Most insects have one or more sensory organs that are sensitive to vibrations transmitted through the air. Insects sense and interpret sounds in order to communicate with other insects and to navigate their environment, however, some insects listen for the sounds of predators in order to avoid being eaten by them.
One such an example are certain hawkmoths which can detect and avoid hungry bats, thanks to a pair of tympanic organs. These auditory organs can detect frequencies from 3-100 kHz, enabling them to hear a pursuing bat’s sonar and take evasive action.
Further to this, it is believed the reason that night-flying moths, such as hawkmoths, are “woolly” (i.e. having a body covering of fine hair) is to absorb sound reflection from echolocating bats and therefore avoid easy detection.
Another interesting strategy is found in various dung beetle species, longhorn beetles and velvet ant wasp species that “chirp” when handled. This is apparently not intended as a warning signal to members of their species as they are all solitary (and since these species are without any specific mechanical or chemical defence mechanisms), nor as a warning to would be predators, but rather a means of escape by reason of the following hypothesis:
Birds are the main predators of these insects, and generally birds instinctively regurgitate food in reaction to the high-pitched ”cheeping” of their nestlings. Thus, when the insect is caught in the beak and it chirps, the sound is relayed through the beak and the skull of the bird to its ears, whereupon the bird will spit out its catch as it is tricked into thinking it is the nestling calling for food!
By definition, camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, i.e. crypsis, or by disguising themselves as something else known as mimesis (mimicking).
A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate.
As an example of mimicry we can look at the caterpillars of the citrus swallowtail butterfly which have evolved to look like bird droppings as a way to avoid being eaten. Most predators don’t enjoy eating bird droppings, so this strategy ensures that swallowtail caterpillars will survive long enough to pupate and emerge as winged adults, which will in turn mate and lay eggs and keep the species going.
Researchers now say that they take the disguise a step further by also changing their posture to look like a lump of excrement when resting on leaves or branches. When they reach their last stage and become an unrealistic size, their coloration and patterning switches to mimic chewed on leaves to further disguise themselves. In addition, caterpillars are also equipped with a gland called an osmeterium which resembles a snakes’ forked tongue, which when threatened, it flicks the tongue-like organ which gives off a pungent citrus smell (due to the consumption of citrus leaves when at the larval stage) to further ward of predators.