by Dr. Harold L. Willis
ABOUT THIS ISSUE
Published by The Kansas State Teachers College of Emporia
Prepared and issued by The Department of Biology, with the cooperation of the Division of Education
Editor: Robert J. Boles
James S. Wilson, Gilbert A. Leisman, Harold Durst, Robert F. Clarke
Online edition by: Terri Weast
The Kansas School Naturalistis sent upon request, free of charge, to Kansas teachers, school board members and administrators, librarians, conservationists, youth leaders, and other adults interested in nature education. Back numbers are sent free as long as supply lasts, except Vol.5, No.3, Poisonous Snakes of Kansas. Copies of this issue may be obtained for 25 cents each postpaid. Send orders to The Kansas School Naturalist, Department of Biology, Kansas Stare Teachers College, Emporia, Kansas, 66801.
The Kansas School Naturalist is published in October, December, February, and April of each year by the Kansas State Teachers College, 1200 Commercial Street, Emporia, Kansas, 66801. Second-class postage paid at Emporia, Kansas.
"Statement required by the Act of October, 1962: Section 4369, Title 39, United States Code, showing Ownership, Management and Circulation." The Kansas School Naturalist is published in October, December, February, and April. Editorial Office and Publication Office at 1200 Commercial Street, Emporia, Kansas, 66801. The Naturalist is edited and published by the Kansas State Teachers College, Emporia, Kansas. Editor, Robert J. Boles, Department of Biology.
This issue of The Kansas School Naturalist was written by Dr. Harold Willis, of the Biology Department of Wisconsin State University at Platteville. He is a graduate of KSTC.
Cover is by Dr. Robert Boles, KSTC Biology Department. Dr. Willis did the drawings. Photographs are by Dr. Willis and Dr. Boles.
by Dr. Harold L. Willis
One of the most fascinating aspects about animals is that some of them are so hard to see, while others are so easy to see. Are there reasons for the colors or patterns that animals have? Most definitely! In the natural world, most animal species are preyed upon by other species, and some of these "potential prey" are themselves predators on other species. Most predators rely greatly on vision to find their prey (exceptions include nocturnal predators, such as scorpions, which rely on the tactile sense, or sense of touch; pit vipers (rattlesnakes, copperheads, etc.), which possess heat-sensitive organs to detect warm-blooded prey; and bats, which use echo location, or "sonar"). Between these predators with good vision and their prey, there is a life and death game of hide and seek. The predator must be well adapted with sense organs and structures for prey capture (claws, fangs, etc. ) in order to catch enough food to survive (while at the same time escaping its own enemies). The potential prey obviously must be adapted to frequently escape being eaten in order to survive as a species. Among various methods of escape (including running, flying, armor, spines, noxious chemicals, bluffing and playing dead ) are several types of protective coloration, sometimes used in combination or with other methods besides color. In this issue we will examine the most common and interesting types, especially those found in midwestern species.
Fig. 1. Underwing moth (Catocala) resting on tree trunk, with front wings camouflaged.
Types of protective coloration can be divided into two main categories, (1) concealment, where the animal's color makes it difficult to see, and (2) conspicuous coloration. Concealment, which is sometimes called
camouflage or cryptic coloration, usually involves an animal that tends to match its background or substrate, or resembles some object in its environment that a predator would not want to eat, such as a twig. Many species of insects, reptiles, and amphibians have a general color resemblance to their usual background, but no other special color adaptations. Green aphids, leafhoppers, caterpillars, tree frogs,
and tree snakes are all found on vegetation. Brown moths (Fig. 1), beetles, lizards, snakes, toads , and mammals are found on either tree trunks or the ground. Most of these brown animals have a mottled or
irregular pattern of darker and lighter shades of brown to resemble bark or soil. Ambush bugs, soldier beetles, and crab spiders sit in flowers (such as goldenrod and other yellow composites) and are yellowish
in color. There are some tropical butterflies with transparent wings which can thus "match" any background color. Most fascinating are such animals as the chameleons and ocean flat fishes (flounder, sole) which can change their color at will to match their background, and can even become spotted, striped, or uniformly colored.
Fig. 2. Effect of countershading: (a) uniformly colored cylinder with shadow, (b) counter-shaded cylinder
without overhead lighting, (c) counter-shaded cylinder that hides the shape.
Besides general color resemblance, some animals have special color patterns or body structures that help
conceal their body contour, outline, or even their shadow, which may be more conspicuous than the animal
itself! The bodies of most animals are more or less cylindrical in shape, or at least round or oval in cross
section. If such an animal has a uniform color and if the sun shines on it from above, the bottom side of the animal will be in shadow and appear darker. while the top side will appear lighter. with the rounded sides intergrading between (Fig. 2A). This would make the rounded body contour conspicuous. To counteract this, some animals (many fishes, birds, mammals, reptiles, and insects) have their bodies colored so that the top is darker, the bottom lighter, and the sides gradually intermediate (Fig. 2B). This is called countershading. When light strikes the animal from above. the shadow is counterbalanced by the darker top side, and the cylindrical body appears flat (Fig. 2C). Besides concealing the shadow on the rounded body, the shadow under the body (on the substrate) can be reduced or eliminated by the animal (a) having a flattened body (or flat flaps projecting out of the body) and clinging close to the substrate, or (b) having a fringe of small projections along where the body meets the substrate. A few tropical insects and lizards have these adaptations especially well developed (Fig. 3).
Fig. 3. Effect of shadow-reducing structures: (a) cylinder with shadow, (b) flattened cylinder with flaps,
(c) Malaysian ground beetle (Mormolyce) with flaps on wing covers, (d) inchworm caterpillar with fringe at base.
Fig. 4. Effect of disruptive coloration: (a) disruptively-colored fish against uniform background,
(b) same fish against natural background.
Fig. 5. South American tree frog (Hyla leucophyllata) with disruptive coloration.
Fig.6. Two examples of tree hoppers.
Most animals have bodies with fairly straight (or smoothly rounded outlines, which make them easier to
spot in an environment made up of many small or irregular structures (jagged tree bark, rocks, vegetation,
etc.). Some species have the usual body outlines, but have disruptive coloration, a color pattern that
visually tends to break up or conceal the body outlines or shape. Generally, disruptive coloration involves light and dark colors that sharply contrast where they meet and form a bold pattern of stripes or shapes (often running in a different direction than the body parts). This bold pattern actually may be conspicuous when seen up close or against a uniform background, but when seen from a distance or against an
Fig. 7. Walking stick in natural habitat.
Fig. 8. Green-colored katydid (Microcentrum) whose color and flowers or old moldy leaves with flattened shape resembles a leaf.
Fig. 9. Butterfly with irregular wing edges (hop merchant, Polygonia comma).
Fig. 10. Gray hairstreak butterfly (Strymon melinus) with false head at posterior end of hind wings.
Fig. 11. Four-eye butterfly fish, with false eye spot and hidden real eye.
Fig. 12. Startle coloration in underwing moth (Catocala): (a) moth in resting position with front wings covering hind wings, (b) moth
with front wings raised to show banded hind wings.
Fig. 13. Caterpillar of spicebush swallowtail butterfly (Papilio troilus) with false eyespots on thorax.
Fig. 14. 10 moth (Automeris io) with eyespots on hind wings.
Fig. 15. American bittern (Botarurus lentiginosus ) showing the striped color pattern and posture that camouflages the bird among aquatic plants.
irregular background, they make the body shape very difficult to discern and provide an excellent camouflage. Some disruptively colored animals have a stripe running across their eye, serving to disguise this conspicuous round organ (Fig. 11). Examples of disruptive coloration include many moths and butterflies, frogs, marine fishes , and some mammals, including the zebra (Figs. 4-5). It is interesting to note how man has copied disruptive coloration (and sometimes countershading) to help camouflage war planes , ships, tanks, and soldiers. Another way of solving the problem of hiding the body outline is found in animals that have very irregular or ragged body outlines, such as a number of butterflies and moths with irregular wing edges (Fig. 9).
Another general type of concealment is called special resemblance, in which not only the color but also the shape of the animal resembles some inedible object in its environment, often to an amazing degree. Common examples found in Kansas include walking sticks (Fig. 7), praying mantids, and inchworm caterpillars, which resemble twigs; katydids which resemble living leaves (Fig. 8) and butterflies in which the bottom surface of the wings resembles a dead leaf; and treehoppers which resemble thorns or jagged bits of debris (Fig. 6) . Some tropical insects even resemble flowers or old moldy leaves with holes chewed by insects.
A final type of concealment is unusual because only part of the body is concealed, the head region, while the opposite end of the body is conspicuous, having a color pattern resembling a false eye or head. These are called deflective or directive markings, since they presumably direct the attack of a predator away from the vital head region toward less vulnerable regions of the body. A common example in Kansas is the small gray hairstreak butterfly, which has its real antennae made inconspicuous by white stripes, but at the rear edge of its hind wings has false antennae and a bright orange area and black eye-like spot (Fig. 10). If a bird should peck away part of the edge of the butterfly 's hind wing, it would not be killed and could probably flyaway before the bird could catch it. Some marine fish have the real eye hidden by disruptive coloration, but have a conspicuous false eye on their tail (Fig. 11).
In the other main type of protective coloration, the animal usually has highly visible colors (red , orange, yellow) and a bold pattern of stripes or spots. Although such coloration would seem to invite predators to attack, the potential prey is protected in often surprising ways (literally!)
There are several types of conspicuous coloration. One involves animals which are primarily camouflaged by any of the methods described above, but also have hidden bright colors or false eye spots that they suddenly expose only when a predator approaches too closely. Thus they rely on surprising the enemy and may be able to escape when the predator hesitates or is frightened. This is called startle or flash coloration and is sometimes used along with sudden sounds or foul smelling chemicals, but usually the animal has no means of protection other than its coloration. False eye spots are an effective protection from predators such as birds, which think the " eyes" belong to a large predator such as a fox or hawk. Common examples in Kansas include the underwing moths, with camouflaged front wings and brightly striped hind
wings (covered by the front wings when the moth is at rest, but suddenly exposed when the moth is disturbed) (Figs. 1-12); band-winged grasshoppers, which sit on the ground and are very well camouflaged, but suddenly fly up, exposing bright hind wings and making a crackling sound; several butterflies and moths which have eyespots on their wings (Fig. 14); and caterpillars with hidden bright colors or eyespots (Fig. 13).
A different sort of conspicuous coloration is called warning coloration. It is found on animals that can defend themselves (with stings, spines, poisons, or noxious, chemicals), and involves conspicuous colors or patterns that are not hidden. According to theory, a predator may attack or even eat a few such animals, but will soon learn to avoid them on sight, thus the species as a whole is protected. Common examples include skunks, certain poisonous tropical frogs, certain caterpillars with stinging spines, bees and wasps, and such insects as ladybird beetles and the monarch butterfly (and its caterpillar), which contain distasteful chemicals (Fig. 19).
The protection gained from warning coloration is taken advantage of by certain species (called mimics) resembling other species (called models). This situation is called mimicry, and there are two main types. One, called Mullerian mimicry, involves two or more species of animals that can defend themselves, mimicing each other. Thus a predator only has to learn to avoid one color or pattern, not several different ones. Two examples found in Kansas include (1) most of the species of stinging wasps and bees, which have yellow and black stripes, and (2) several distasteful insects that feed on milkweed, which are red and black or orange and black, including the monarch butterfly, a moth caterpillar, a long-horned beetle, and a leaf beetle.
The second type of mimicry, Batesian mimicry, involves a model that can defend itself and a mimic that cannot. Both usually have warning coloration, so the defenseless mimic is protected if the predators have learned to avoid the models. The resemblance of the mimic to the model is often amazingly close and has even fooled professional biologists! Many examples are found in Kansas; one is the viceroy butterfly, which looks very similar to the distasteful (to birds) monarch. The two species are not closely related, and
the closest rela ti ve to the viceroy is the red-spotted purple, which is completely different looking and dark colored. Many other cases of mimicry among butterflies are found in the tropics. A surprising number of
insect mimics have the yellow and black stripes (and often body shape and behavior) of stinging wasps or bees, including many syrphid flies, bee flies, a robber fly, wasp moths, clear-winged moths, a sphinx moth,
some long-horned beetles, as well as others (Fig. 16). A few insects mimic ants, which do not have warning coloration, but do have a distinctive shape to advertise their stinging capabilities.
ORIGIN OF PROTECTIVE COLORATION
Now that we have examined the most common types of protective coloration, we should consider how such unusual and often fantastic adaptation originated. The commonly accepted idea among biologists is that
such adaptations (as well as most others) have been produced, or at least perfected by natural selection. In this process, any change in the color or shape of an animal (produced either from random gene combinations during the reproduction of each generation or by mutations, sudden changes in genes or chromosomes) may play a great role in determining whether it escapes its enemies and survives to reproduce. If a change occurs that better camouflages the species (or produces a more effective conspicuous coloration), those individuals that have the changed characteristic will most likely escape predators and pass on their genetic characteristics to the next generation (or in other words, the less well adapted individuals are eliminated by predators). Thus, over many generations the species can change or evolve to become better adapted, which may include protective coloration. We should not overlook the fact that in most cases, not only the color or shape of the animal is important in escaping its enemies. but also its behavior. Thus most camouflaged species tend to remain relatively motionless during the day. On the other hand, warningly colored species are quite active and Batesian mimics imitate the behavior of their model. Species with startle coloration at first remain still, but when their camouflage fails, they exhibit their special coloration and attempt to escape. Behavior is also controlled by genes and can also evolve to better adapt the species for survival.
It is fascinating to become familiar with the many examples of protective coloration which you can find around you. Simply walk around in various habitats and observe various species that are protectively colored (some will be very difficult to observe). Record your observations in a notebook. If you have a camera, try to take pictures (especially in color) of the examples you find. and build up a picture collection. Or you may be able to collect and preserve the animals themselves, especially the insects. You can make an interesting display of protective coloration types, using pictures and specimens. For types of concealing coloration, you can glue dried specimens of insects to a natural background (a piece of bark, twigs, leaves. soil, etc.), to show how well camouflaged they are.
Fig. 16. Batesian mimicry: (a) a wasp, the model, (b) a flower fly; (c) a clear-wing moth; (d) a long-horned
beetle ; (e) a bumblebee, the model; (f) a robber fly; (g) a sphinx moth.
|Fig. 17. Disruptive coloration in snakes:
(a) copperhead against unnatural background,
(b) copperhead against natural background,
(c) albino rattlesnake, lacking disruptive coloration.
|Fig. 18.Horned lizard (Phrynosoma cornutum) with irregular body outline.|
|Fig. 19. Gila monster (Heloderma suspectum), with orange and black warning coloration.|
Cott, H. B. 1940 (1957) . Adaptive coloration in animals. Methuen & Co. Ltd., London. 508 p., 48 pls.
Portmann, A. 1959. Animal camouflage. Univ. of Michigan Press, Ann Arbor. 111 p.
Wickler, W. 1968. Mimicry in paints and animals. McGraw-Hill Book Co ., N. York. 255 p.
A "CAMOUFLAGE" QUIZZ
You may reveal the answers by moving your cursor and selecting the text located within the box at the bottom.
|The animals in these photographs rely upon their coloration and/ or shapes to help them escape detection. See if you can locate and identify each of them.||(1) ptarmigans, (2) baby avocet, (3) leopard frog, (4) grasshopper, (5) praying mantis, (6) wolf-spider|
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