Soldiers of the Óglaigh na hÉireann (Irish: 'Volunteers of Ireland') on patrol in East Timor. The Irish Defence Forces frequently participate in United Nations peace-keeping missions and humanitarian relief operations. [Image: Name withheld by request.]
Crypsis, for beginners
Contrary to popular belief, camouflage doesn't work by making its wearer invisible. Rather, it works by creating visual confusion, and thereby disguises a recognisable form by breaking up its outline.
In war, the function of camouflage is easy to understand: it is used to hide yourself and your equipment from the enemy. People have used camouflage, of one sort or another, since prehistoric times. Still, the practice of camouflage predates humankind, as evidenced by the natural adaptations that allow animals to blend with their environments.
In nature, every advantage increases an animal's chances of survival and, by extension, its chances of reproducing. From among all of the special adaptations that help animals to find food and to avoid becoming food, natural camouflage — an animal's abilty to hide itself from predator and prey — is probably the most widespread and varied. Zoologists frequently refer to any animal's ability to hide, disguise or otherwise conceal itself as crypsis.
Crypsis in nature
The term crypsis comes from the late Latin crypticus, which is derived from the Greek kruptein, 'to hide'; and the colours and patterns displayed in natural camouflage are called cryptic colours and patterns.
In nature, there are two types of cryptic camouflage pattern: mimetic camouflage and disruptive camouflage.
Crypsis by mimetic camouflage
The word mimetic derives from the Greek mimos, 'imitator'. Thus mimetic camouflage obviously aims at disguising the animal as something else.
Sometimes these disguises are rather simple, because some animals are able to blend with their environments through the use of only a single color. A polar bear's white fur or the green sclerites that comprise a grasshopper's exoskeleton are two good examples of the simplest kind of mimetic camouflage.
However, mimetic camouflage can also be very elaborate, involving not only colour but morphology, as well. For example, Megophrys nasuta, a species of frog found on the Malay Peninsula, has a spindly nose and strange horns and peculiar ridges that, in conjunction with a coloration that can include dark chocolate brown, pale biege, or even russet, essentially make the animal 'disappear', when it is placed among the leaf-litter of the forest floor.
Crypsis by disruptive camouflage
Disruptive camouflage, on the other hand, aims to break up the animal's body shape and outline. Many animals have evolved distinctive patterns, which conceal them, because it is a very effective adaptation. It is also a very economical one, since it usually involves only colour and pattern.
One simple type of disruptive camouflage is countershading, which defeats a predator's ability to identify prey by shape. In countershading, the upper parts of an animal are dark and its lower parts are light. This reverses the normal distribution of luminance on objects, which are usually lit from above. The predator's eye is drawn to the lighter areas and, since the brain interprets the contrast between light and dark as a natural boundary, it is discouraged from 'putting together' the two areas and perceiving a single object.
Many animals display even more elaborate patterns of contrasting patches, spots or stripes. A zebra's stripes, for example, are so striking a design that it is difficult to imagine how they could possibly function as camouflage; after all, black and white are not colours often seen in the environment. Nonetheless, zoologists believe that these stripes serve to conceal zebras from predators in at least two different ways.
At its most fundamental level, the pattern of contrasting stripes breaks the overall shape of the animal into smaller, irregular shapes. Again, attention is drawn to the white areas, while the intervening black areas discourage the brain from perceiving a single object. Were a single zebra standing still in an environment of strong highlights and deep, vertical shadows, it is even possible that a predator might completely overlook it.
Zebras, however, are herd animals; and it is extremely unlikely that a predator could fail to notice a large group of black-and-white striped prey. This is when the zebra's stripes serve their second — and, perhaps, more important — function; the pattern of each zebra's stripes blends with the stripes of the other zebras around it. This kind of camouflage is called boundary disruption, and it confuses the predator. Seeing only a large, moving, striped mass rather than many individual zebras, the predator would have trouble picking out any one zebra; and so it would be unable to decide upon the best plan of attack.
Copyright © 2005, 2008 Brad Turner. All rights reserved.