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Butterfly Gardening for Texas
By Geyata Ajilvsgi Texas A&M University Press
Copyright © 2013 Geyata Ajilvsgi
All rights reserved.
ISBN: 978-1-60344-957-1
CHAPTER 1
Understanding the Butterfly
Butterflies, along with moths, are easily differentiated from all other insects. They belong to the order Lepidoptera, a name composed of two Greek words, lepis meaning "scale" and ptera meaning "wing," combined to mean "scale-winged," which aptly describes their most obvious feature. The wings, as well as the body, are almost always entirely covered with scales. Scales on the wings are usually flat, but the scales covering the body are often long and silky, appearing almost hairlike.
In most respects butterflies and moths are quite similar, but four characteristics usually separate them. In almost all species of butterflies, the antennae end in a club or swelling at the tip, while the antennae of moths are slender or feathery but rarely clubbed. Also, butterflies generally fly during the day, while moths fly primarily at night. However, there are numerous exceptions to the generality concerning moths, since many fly about during the day. Another defining characteristic is that butterflies usually rest with their wings closed and held vertically over the back. Exceptions to this occur during periods of basking when the wings of most species may be spread flat, and the Skippers frequently rest with their wings half spread. Conversely, most moths rest with their wings outstretched and held flat against the surface on which they are resting or drawn back tightly along the sides of the body. Last, and as a general rule, butterflies more often form an unprotected chrysalis in the open, while moths form a tough, silken cocoon in which to pupate.
Life Cycle
In their life cycle, butterflies go through four distinct stages, together known as a complete metamorphosis. These stages of growth are the embryo stage (egg or ovum), the wormlike growing stage (caterpillar or larva), the mummylike transition stage (chrysalis or pupa), and the winged reproductive stage (adult or imago).
Adult females usually lay eggs on or near the food plant that will sustain the caterpillars or larvae upon hatching. The eggs are almost always left unattended and will usually hatch in a few days. In some species eggs are left to overwinter, and in some rare cases they will not hatch for two years or more.
Eggs are very soft when first laid and are usually attached firmly to the food source with a sticky, gluelike substance. Slowly, the egg takes on its particular form and color as the shell dries and hardens. Shape is usually characteristic for the species, and under magnification each egg reveals its own beautiful markings and coloring. It may be round, domed, flattened, elongated, or shaped like a minute barrel, urn, pincushion, spindle, or sea urchin. The egg surface may be pearly smooth or elaborately sculptured with raised or sunken ribbing, horizontal furrows, pits, grooves, knots, spikes, or other ornamentations. Eggs of the Cabbage White (Pieris rapae) are fat yellow cones with intricate lengthwise striations. The Pipevine Swallowtail (Battus philenor) lays large, reddish-brown, almost perfectly spherical eggs, while eggs of the Guava Skipper (Phocides polybius lilea) resemble beautifully ribbed and flattened turbans. Eggs of the Blue Metalmark (Lasaia sula) resemble two pies, one stacked on top of the other.
Females of each species instinctively choose the exact food plant on which to deposit their eggs, using an intricate detection system that involves sight, feel, taste, and smell. Many butterflies lay their eggs singly, but others attach several in a single layer or in clusters of up to five hundred, usually to the underside of a leaf. Depending on the species, a female may lay between one hundred and two thousand eggs during her lifetime.
Immediately upon hatching, the young caterpillar usually eats all or a portion of the eggshell as its first meal, thus gaining vital nutrients that have been passed on from the mother. With many species the eating of the shell is extremely important, for the young larvae will not survive if they do not do so. The caterpillar then begins feeding on the leaf or flower it is on. In this nutritive stage of the larva's life, its entire purpose is to eat—and eat it does. As it grows, it ravenously consumes food at an astonishing rate. By the time the larva has finally become satiated, it may have increased its weight by as much as one thousand times.
Some caterpillars, such as those of the Clouded Sulphur (Colias philodice), are cannibalistic in the sense that they consume eggs or already-formed chrysalides along with foliage if they happen to be attached where the caterpillar is feeding. Caterpillars of another butterfly, the Harvester (Feniseca tarquinius), eat only woolly aphids (family Eriosomatidae) for its food.
The skin, or exoskeleton, of a caterpillar is incapable of stretching, so to grow any larger, a caterpillar must shed the old, too-tight skin for a new one. Through a complicated process, the skin splits down the back, and the larva emerges with a totally new skin. At first the new skin is much too large, but as the caterpillar continues to eat, this skin eventually becomes stuffed to bursting. Again the splitting process is repeated, and the larva emerges with yet another loose skin to be filled up. This changing of skins is called molting. After each molt the old skin may be abandoned but is more commonly eaten by the caterpillar.
A caterpillar will go through this process several times, the number of molts varying with the species. Most Blues and Hairstreaks (family Lycaenidae) molt only four times, while many of the Metalmarks (family Riodinidae) change skins from four to nine times. The period of a caterpillar's life between each molt is called a stage or an instar, and the new skin of each instar is often colored and patterned differently from the previous one.
At the end of the last instar, the insect is ready to begin the last phase of its caterpillar life and seeks the most protected place possible. Caterpillars of many butterflies will choose a stem or branch, securely attaching themselves with strands or small pads of silk. Others pupate in silk-lined leaf-nests made from their respective food plants or in ground debris at the base of the food plant. During this transformational phase, sometimes requiring several hours, the caterpillar slowly undergoes a complete change inside the skin and eventually sheds the skin to emerge in a totally different shape—as the chrysalis or pupa. In this form it will remain, mostly immobile and helpless, for several days, months, or in a few instances, years. During this period of its life, the butterfly is vulnerable and open to attack by all sorts of enemies, such as ants, parasitic wasps, birds, lizards, and environmental factors. It is only natural, then, for the caterpillar to seek a protected place when the time comes to pupate.
When the appropriate, species-specific time is completed, yet another change takes place within the pupal case. The cells have multiplied, changed, and rearranged into the various parts of the soon-to-be adult butterfly. The chrysalis changes color; its outer skin becomes almost transparent, and the wing colors of the butterfly become visible inside. After finally splitting the pupal shell and freeing its head, the butterfly uses its legs and contortions of the body to free itself. While it remains motionless, fluids are slowly pumped into the veins of the crumpled wings until completely expanded and dried into their beautiful colorings and patterns.
The Body
The body of a butterfly is separated into three main divisions: the head, thorax, and abdomen. The head bears the principal sense organs, one of the most obvious being the pair of antennae projecting from the top of the head. Each antenna is composed of short joints or segments, with segments near the tip being larger and causing the antennae to appear knobbed or clubbed. The antennae are quite movable and are used for balancing, touching, hearing, and tasting. Also, most of the main detection sites of smell are situated in the tips. Not having long-distance vision, the butterfly depends more on this sense of smell for detecting odors in search of food. At the base of each antenna is a most essential organ used for orientation, especially while flying.
Enormous, almost hemispherical compound eyes are just below the antennae. They are among the most complex and intricately designed mechanisms used by animals for seeing. The shape, structure, and position of the butterfly's eyes enable it to see in all directions except directly beneath its body. The eyes are called compound because they are actually made up of thousands of honeycomb-like facets—between two thousand and twenty thousand facets, depending on the species. Instead of seeing a single light image or object, the butterfly sees a separate image with each tiny facet, making thousands of images. These images are then integrated by its brain into a mosaic picture.
Its eyes are well suited for detecting any type of nearby movement, including butterflies of the opposite sex as well as numerous predators. The eyes are fixed and cannot move, rendering the insect unable to keep objects approaching it in focus. Instead, as the butterfly nears an object (or the object nears it), images move toward the inner part of each eye, with the visual angle decreasing. The spectral or color range visible to the butterfly extends from ultraviolet through yellow-orange and red, fully covering the visual spectrum of humans as well as that of other insects. This mechanism gives the butterfly the broadest spectrum of color vision known to exist in the animal kingdom.
The ability to recognize more colors gives the butterfly many advantages in communication, feeding, protection, and perpetuation of young. Besides the colors visible to us, a butterfly's wing may reflect a little or a lot of the ultraviolet spectrum to another butterfly. This ultraviolet coloring plays an important role in courtship and mating. Also, since vegetation generally absorbs ultraviolet light, reflection from flowers and foliage serves to maximize color contrast, thus aiding the female butterfly in plant identification for egg deposition.
Also on the head, situated below and extending upward to the side of the eyes, are two soft, furry or scaly palpi. The palpi are sensitive receptors that test the suitability of the food source and protect the mouth and proboscis. The proboscis is divided into two grooved parts or half tubes that are separated when the butterfly first emerges from the pupal shell. The butterfly must spend several minutes twisting and turning the parts to fasten them together securely by the interlocking spines along the edges of each half. This structure, which now forms a long, hollow, flexible tube much like a drinking straw, can be rolled up tightly or unrolled at will and is used to suck up liquid food. Some species of butterflies also have thick, tubular organs for tasting near the tip of the proboscis.
Behind the head is the thick, muscular thorax, divided into three segments and bearing six legs and four wings. Each segment of the thorax has two jointed legs, one on each side of the body. In some species of butterflies, such as the Brush-footed (family Nymphalidae), legs on the first segment are undeveloped, held close to the body, and rarely used, causing the butterfly to appear to have only four legs. The last portion of each leg consists of five tiny segments that form the foot with the last segment ending in a pair of claws. These feet possess organs that enable the butterfly to taste its food. Tasting with the feet triggers an automatic, reflex action that causes the proboscis to uncoil when food is found. In some instances, the female uses the clawed segment to scratch the surface of plant leaves and stems, testing the chemical content to determine if it is the proper plant for depositing her eggs.
Above the last two pairs of legs on the thorax are the four wings. Each butterfly wing consists of two delicate membranous sheets with an inner framework of hollow, tubelike veins between the layers. This venation helps strengthen the wings and is in a distinct pattern for most families and species, becoming an important tool in identification. The membrane of the wings is usually transparent, but in most butterflies it is completely covered with thousands of tiny, flat or hairlike scales of various shapes and colors. These scales, shingled in overlapping rows, provide insulation from the cold, protection from rain or dew, and help in flying. They are extremely fragile and, if touched, will readily adhere to the fingers, appearing as colored dust.
The third portion of the butterfly's body is the abdomen, which consists of eleven segments, although only seven or eight can readily be seen. The abdomen is very soft and contains the digestive and reproductive organs. At the tip of the abdomen of the male is a pair of grasping organs used to clasp the female during mating. The abdomen of the female is usually much larger than the male's due to the large mass of unlaid eggs.
Courtship
Butterflies search for a mate primarily by either perching or patrolling, and almost always it is the male who does the courting. In perching behavior, at a specific time of day the male chooses a certain place—such as a rock, a patch of ground, a post, or a particular tree branch—that offers a visual observation point. There he waits until some moving object comes into view. Since his sight is limited to close-up vision, he must inspect everything that comes into his range of sight, be it wasp, bird, dog, cat, squirrel, human, or a butterfly of any species. If the object turns out to be an unacceptable female, the male returns to his perch to wait for the next passerby. If a male encounters another male of the same species, great exhibitions of "fighting" occur, where the two fly in close association, often spiraling upward until almost out of sight, before breaking apart and going their separate ways. The female of each species is instinctively drawn to likely spots that the male of that species ordinarily chooses, so finding a mate is not usually a problem.
The second method used in seeking a mate is patrolling. A patrolling male flies from one end of a selected site to the other almost continuously until a female of the same species flies into the territory. Here again the female is genetically keyed to locate areas typically selected by the male.
The male butterfly uses a variety of ways to recognize and attract a female of the same species. One way is by color and its placement on the wings. Since butterflies see the colors humans see, as well as a large range within the ultraviolet spectrum, the male butterfly sees the colors of a female butterfly's wings entirely differently from how humans see them.
Scale coloration is wondrously complicated. Basically, it is of two types, pigmented and structural. Pigmented colors are actual colors, produced by a pigment within the insect itself or derived from the food plant of the caterpillar. The majority of such colors as blacks, grays, tans, browns, brownish-reds, and some yellows are forms of the chemical melanin, the same pigment that produces freckles and suntans in humans. Ivory to dark yellow colors are usually from organic dyes called flavones, which are retained from the larva's food plant. The yellow coloring of the Sulphurs and Yellows (family Pieridae) is produced by pterines, which are derived from an excretory uric acid. While some white coloring is made from pigment, others are the result of bubbles of air. The scattering of light by transparent particles produces a white effect in the same way that snow appears white. White hair in humans is similarly produced by tiny air bubbles within the strand of hair that replace the natural color rather than by a white coloring substance.
Some of the most striking and beautiful colors, such as most of the blues, greens, golds, and silvers, are the iridescent colors that are due to structural features of the scales or hairs rather than pigmentation. Each scale may be ridged or grooved with microscopic striations. The colors are the result of light being reflected from these physical features, much in the same manner as light refracting off a film of oil on water, which produces glittering, changing colors. Although each scale is of only one color, as a general rule there is a mixture of pigmented and structurally colored scales on almost every species of butterfly. On some, such as the Sulphurs, iridescence can hardly be noticed, but on the Common Buckeye (Junonia coenia) or Pipevine Swallowtail, the glow and shimmer are spectacular.
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Excerpted from Butterfly Gardening for Texas by Geyata Ajilvsgi. Copyright © 2013 Geyata Ajilvsgi. Excerpted by permission of Texas A&M University Press.
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