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Lepidoptera

(butterflies, skippers, moths)

 

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Unit I

General Features

Cesa

 

Palaeochrysophanus candens from North Turkey Cesa

 

 

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Introduction to the Entomology List of the Butterflies of Jordan

Unit II : Classification 

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Contents of the Unit I:

Brief description

Importance of the Lepidoptera

General Features

Life cycle

Egg

Caterpillar

Pupa

Adult:

Head, Compound eyes, Chaetosemata, Frons, Antennae, Mouth-parts

Thorax

Wings, Veins, Scales

Abdomen

Reproduction system of the adult and the external genitalia

Ecology

Behaviour

Food selection by the adult

Migration

Environmental hazards

Protection against danger

 

 

Brief description

The life cycle of Lepidoptera is that common to the higher orders of insects and consists of four stages: egg, larva (caterpillar), pupa (chrysalis), and adult (imago). The larva and adult are almost invariably plant eaters. The larvae do most of the eating, the majority of them feeding on foliage, although many species eat stems, roots, fruits, or flowers. A number of moths and a few butterflies are important pests in agriculture or forestry, invariably as larvae. The adults of many species are important pollenizers, visiting flowers for nectar. In the ecology of most land environments the Lepidoptera are important as transformers of immeasurably large amounts of plant matter into animal matter, which then serves as food for many other groups of animals.

Many members of the order, especially the butterflies, have appealed to the human imagination for thousands of years, as symbols of fragile and ephemeral beauty. References to them abound in literature; and they have been depicted in many paintings, have inspired the designs of jewelry, ornaments and textiles, and even occur in many heraldic devices and on postage stamps. They are the most popular of insects among amateur collectors and students of natural history. Back to the Contents

The caterpillar (above), the pupa (left) and the imago (right) of the species Aporia crataegi from Central Turkey Cesa  

 

 

 

Importance of the Lepidoptera

Among the other insect groups butterflies and moths play an important role as agents of pollen dispersal. The evolution of moths and butterflies (Lepidoptera) was made possible only by the development of the modern flower, which provides their food. Nearly all species of Lepidoptera have a tongue, or proboscis, especially adapted for sucking. The proboscis is coiled at rest and extended in feeding. Hawkmoths hover while they feed, whereas butterflies alight on the flower. Significantly, some butterflies can taste sugar solutions with their feet. Although moths, in general, are nocturnal and butterflies are diurnal, a colour sense has been demonstrated in representatives of both. Generally, the colour sense in Lepidoptera is similar to that of bees, but swallowtails and certain other butterflies also respond to red colours. Typically, colour and fragrance cooperate in guiding Lepidoptera to flowers, but in some cases there is a strong emphasis on just one attractant; for example, certain hawkmoths can find fragrant honeysuckles hidden from sight.

Typical moth flowers e.g., jimsonweed, stephanotis, and honeysuckle are light-coloured, often long and narrow, without landing platforms. The petals are sometimes fringed; the copious nectar is often in a spur. They are open and overwhelmingly fragrant at night. Butterfly flowers e.g., those of butterfly bush, milkweed, and verbena are conspicuously coloured, often red, generally smaller than moth flowers, but grouped together in erect, flat-topped inflorescences that provide landing space for the butterflies.

Many hundreds of Lepidoptera injure plants useful to man, including some of his most important sources of food, fabrics, fodder, and timber. The great majority of the injurious species are moths, and the most injurious life stage always is the larva. Unlike members of other insect orders, the Lepidoptera do not act as carriers of plant diseases, nor are any of them parasites or predators of man or domestic animals.

The list of valuable plants subject to damage by Lepidoptera is a long one, including many grains, sugar beets and cane, cotton, tobacco, some root crops and leaf crops, many fruits, and timber and shade trees. The damage may involve the leaves, stems, roots, or fruit. Woollens, furs, silk, and even feathers are eaten by tineid moths of several genera (clothes moths). The wax moth (Galleria mellonella) causes considerable damage in beehives.

A few Lepidoptera are directly beneficial to man. Nearly all silk is obtained from the completely domesticated silkworm, Bombyx mori, originally Asiatic. Such other silks as shantung and tussah are the products of various Asiatic Saturniidae. The larvae and sometimes the adults of a few species are used for food. The larvae of a skipper, Rhopalocampta libeon, are collected in large quantities in the Congo, and the caterpillars of giant skippers (Megathymidae), known in Mexico as "gusanos de maguey", are canned and exported for consumption as hors d'oeuvres.

The South American cactus moth, Cactoblastis cactorum, has been highly beneficial in weed control, clearing more than 60 million acres of Australia of prickly pear cactus. Doubtless man benefits also from much unrecognized weed eating by caterpillars and flower pollination by adults.

Many Lepidoptera are valuable in biological research, including work in ecology, biogeography, systematics, genetics, and physiology. Much of the present knowledge of endocrine controls of insect development has come from studies of the silkworm moth (Bombyx mori) and various saturniid moths. The study of industrial melanism (an increase in the frequency of black individuals in a population, brought on by the environmental changes that accompanied the Industrial Revolution) in the British peppered moth (Biston betularia) has profoundly influenced modern ideas about rates of evolutionary change. Back to the Contents

 

 

 

General Features

The members of the order show great diversity in size and development rates. The smallest moths have wing expanses as small as 4 millimetres, while the largest moths and butterflies may expand to nearly 300 millimetres. Fast developing species may complete their development in as little as three weeks, while slower ones may take as much as two, or even three, years. Both moths and butterflies occur on every continent except Antarctica. Though they are enormously more numerous and diversified in the tropics, at least some species occur at the limits of polar vegetation. There are many successful species in nearly every land environment, from arid deserts and high mountaintops to marshes and tropical rain forests. Most of the species have become adapted for life in relatively restricted ecological niches, and may be limited to only one or a small group of food plants, often to only a single part of one plant. They are therefore seldom abundant in more than one type of habitat. A few species, however, with broader food habits, may occasionally reach peaks of abnormal abundance and defoliate large areas of such environments as deciduous forest or grassland. Some of the insects most injurious to man's interests in agriculture, forestry, and households are members of the Lepidoptera.

The large family-level groups, and many smaller ones, are worldwide in distribution, with such families as Noctuidae, Geometridae, Pyralidae, and Argynnidae (=Nymphalidae) being dominant elements of the insect fauna of every geographic region. A few families, some subfamilies and a great many genera, however, are characteristically more abundant in one faunal region than in others. Thus, the Neotropical region (mainly Central and South America) is characterized by great diversity of such moth families as the Dioptidae, Pericopidae, and Ctenuchidae and such butterfly subfamilies as the Riodininae, Heliconiinae, Ithomiinae, Morphinae, and Dismorphiinae. The North American (Nearctic) and Eurasian (Palaearctic) faunas show many evidences of close recent connections, chiefly between Asia and western North America. Each region has, however, many distinctive generic-level groups; for example, in the Palaearctic, Erebia and other satyr butterflies, and the parnassians (Papilionidae); in the Nearctic, the underwing moths Catocala (Noctuidae) and the silverspot fritillaries (Argynnidae); in the Ethiopian (African) region, the butterfly genera Charaxes (Nymphalidae) and Teracolus (Pieridae), and many members of the papilionid subfamily Acraeinae; in the Oriental region, Troides (Papilionidae) and Delias (Pieridae).

Many Lepidoptera occur in isolated colonies as relict (remnant) populations, cut off from relatives elsewhere by geologic or climatic changes. Australia and New Zealand have unusually diverse relict populations of the primitive Micropterigidae and Hepialidae. In North America, Europe, and Asia many relict species have survived since the Pleistocene glaciations on isolated southern mountaintops. They include members of such genera as Oeneis and Erebia (Satyridae), Boloria (Argynnidae), Parnassius (Papilionidae), Anarta (Noctuidae), and Pediasia (Pyralidae).

Back to the Contents

 

Life cycle Back to the Contents

 

Egg

The number of eggs laid varies greatly from fewer than a hundred in some species to more than a thousand in others. The eggs are almost always laid in a specific way, usually on or in a suitable foodplant, which the caterpillar, after it is hatched, is destined to live, and the female reveals wondeerful instinct in selecting plants which are appropriate to the development of the larva. As a rule, the larvae are restricted in the range of their food-plants to certain genera, or families of plants. The eggs of many species are laid singly, sometimes in small clusters, sometimes in a mass that may be covered with a hardened secretion of the female's abdominal glands.

 Eggs of Araschnia levana from Germany Cesa

 

In a few groups the terminal segments of the female's abdomen are greatly elongated and bladelike, and the eggs are laid in soft plant tissues or in narrow slits or crevices. In some of the primitive hepialid moths and in some butterflies the female may merely scatter the eggs in flight in the general vicinity of a suitable foodplant. Development of the embryo and emergence of the young larva is often controlled by a mechanism of physiologically enforced inactivity (diapause), which has the effect of timing the emergence of the larva to coincide with suitable conditions of weather and the growth of the foodplant. Respiration in the egg is carried on through an aeropyle, a system of air passages in the chorion (shell) that enables oxygen exchange with the environment to occur whether the egg is dry or wet. In a few species (some tineid moths and pierid butterflies) the larvae hatch in the uterus of the female.

The forms of the eggs are various. Some are spherical, others hemispherical, conical, and cylindrical. Some are barrel-shaped; others have the shape of a cheese, and still others have the form of a turban. Theis surface is variously ornamented. Sometimes they are ribbed, the ribs running from the center outwardly and downwardly along the sides like the meridian lines upon a globe. Between these ribs there is frequently found a fine network of raised lines variously arranged. Sometimes the surface is covered with minute depressions, sometimes with a series of minute elevations variously disposed. As there is great variety in the form of the eggs, so also there is great variety in their colour. Brown, blue, green, red, and yellow eggs occur. Greenish or greenish-white are common tints. The eggs are often ornamented with dots and lines of darker colour. Species which are related to one another show their affinity even in the form of their eggs. At the upper end of the eggs of insects there are one or more curious structure, known as micropyles (little doors), through which the spermatozoa of the male find ingress and they are fertilized. These can only be seen under a good microscope. Back to the Contents

 

Caterpillar

The second stage of the Lepidoptera is known as the caterpillar or the larval stage. In general caterpillarshave long, worm-like bodies. Frequently they are thickest about the middle, tapering before and behind, flattened on the under side. While the cylindrical shape is commonest, there are some families in which the larvae are short, oval, or slug-shaped, sometimes curiously modified by ridges and prominences. The body of the larvae of lepidoptera consists normally of thirteen rings (segments), the first constituting the head. Head of larva is always conspicuous, composed of horny or chitinous material, but varying exceedingly in form and size. It is very rarely small and retracted. Generally large, hemispherical, conical or bilobed. In some families it is ornamented by horn-like projections. On the lower side are the mouth-parts, consisting of the upper lip, the mandibles, the antennae or feelers, the under lip, the maxillae, and two set of palpi, known as the maxillary and labial palpi. In many genera the labium is provided with a short, horny projection known as the spinneret, through which the silk secreted by the caterpillar is passed. On either side, just above the mandibles, are located the eyes, or ocelli, which in the caterpillar are simple, round, shining only to be clearly distinguished by the aid of a magnifying-glass. These ocelli are frequently arranged in series on each side. The palpi are organs of touch connected with the maxillae and the labium, or under lip, and are used in the process of feeding, and also when the caterpillar is crawling from place to place. The larva appears to guide itself in great part by means of the palpi.

The body of the caterpillar is covered by a thin skin. It is composed of segments, the first three of which, back to the head, correspond to the thorax of the perfect insect (adult), and the last nine to the abdomen of the butterfly. On each ring, with the exception of the second, the third, and the last, there is found on either side a small oval opening known as spiracle, through which the creature breathes. As a rule, the spiracles of the first and eleventh rings are larger in size than the others.

Every caterpillar has on each of the first three segments a pair of legs, which are organs composed of three somewhat horny parts covered and bound together with skin, and armed at their extremities by a sharp claw. These three paris of feet in the caterpillar are always known as the fore-legs, and correspond to the three pairs legs in the adult insect. In addition, in most cases, we find four pairs of prolegs on the underside of the segments from the sixth to ninth, and another pair on the last segment, which latter pair are called the anal prolegs. These organs, whcih are necessary to the life of the caterpillar, do not reappear in the perfect insect, but are lost when the transformation from the caterpillar to the chrysalis takes place.

The bodies of caterpillars are variously ornamented. Many of them are quite smooth; many are provided with horny projections, spines, and eminences. The colouration of caterpillars is as remarkable in the variety. As caterpillars, for the most part, feed upon growing vegetation, multitudes of them are green in colour, being thus adapted to the surroundings and securing a measure of protection. Many are brown, and exactly mimic the colour of the twigs and branches upon which they rest when not engaged in feeding.

Caterpillars vary in their social habits. Some species are gregarious, and are found in colonies. These frequently build for themselves defenses, weaving webs of silk among the branches, in which they are in part protected from their enemies and also from the inclemencies of the weather. Most caterpillars are, however, soliary, and no community life is maintained by the vast majority of species. Back to the Contents

Pupa Back to the Contents

Adult Back to the Contents

Head: Back to the Contents

Compound eyes large, rounded, often with erect hairs between the facets. Ocelli if present paired, one above each eye.

Both sexes sometimes with paired sensory organs (chaetosemata). Back to the Contents

Frons and clypeus sometimes separated by an epistomal suture, or not differentiated (frontoclypeus). Genae narrow. Labrum as a narrow, pointed or transverse plate, with laterally projecting pilifers and median projection (epipharynx). Back to the Contents

Antennae anterior to ocelli, many- segmented, usually partly clothed with scales, but sometimes naked. Scape sometimes with tuft of scales, or with anterior pecten of hair-like scales, or laterally expanded and concave beneath forming an eye-cap. Clavola (antennal flagellum) in male usually

more specialized than in female, varying greatly in structure (1.moniliform, 2.filiform, ciliate, 7.clubbed, 4. serrate, 5. Serrate, 9. lamellate, or pectinate, etc.). Back to the Contents

Mouth-parts variable. Mandibles usually absent, rarely functional, dentate (Zeugloptera), or non-dentate (Dachnonympha), in both furnished with well-developed abductor and adductor muscles, or vestigial (a few families). Maxillae with laciniae present (Zeugloptera, some Dachnonympha), rudimentary or absent. Galeae often greatly elongated, usually grooved internally, and fastened together by interlocking hooks and spines to form a tubular proboscis (haustellum) through which liquid food may be drawn. Haustellum often with dense overlapping scales towards base; it is composed of a large number of sclerotized rings joined together by membraneous bands, each half containing a nerve, a trachea, and two sets of muscles which enable it to be coiled beneath the head when not in use. Back to the Contents

Wings

The wings of butterflies consist of a framework of horny tubes which are in reality double, the inner tube being filled with air, ths outer tube with blood, which circulates most freely during the time that the insect is undergoing the process of development after emergence from the chrysalis, as has been already described. After emergence the circulation of the blood in the outer portion of the tubes is largely, if not altogether, suspended. These horny tubes support a braod membrane, which is clothed in most species upon both sides with flattened scales which are attached to the membrane in such a way that overlap one nother like the shingles on a roof. These scales are very beautiful objects when examined under a microscope, and there is considerable diversity in their form as well as in their colours. The scales of males of many species have pecularly shaped scales arranged in tufts and folds, which are called androconia, and are useful in microscopically determining species.

The portion of the wings which is nearest to the thorax at the point where they are attached to the body is called the base; the middle third of the wing is known as the discal area, the outer third as postdiscal (or limbal) area. The anterior margin of the wings is called the costal margin; the outer edge is known as termen (or external margin), the inner edge as the inner margin (or dorsum). The shape of the wings varies very much. The tip of the anterior (front, or fore-) wing is called the apex, and this may be rounded, acute, falcate (somewhat sickle-shaped), or square. The angle formed by the outer margin of the wing with the inner margin is commonly known as the outer angle (or anal, tornus).  A knowledge of these terms is necessary in order to understand the technical descriptions which are given by the authors.

The veins in both the fore- and hind-wings of butterflies may be divided into simple and compound veins. In the fore-wing the simple veins are the costal, the radial, and the anal; in the hind-wing, the costal, the subcostal, the median, the cubital, the anal veins are simple. The costal vein in the hind-wing is, however, generally provided near the base with a short ascending branch which is known as the precostal vein. In addition to these simple veins there are in the fore-wing two branching veins, one immediately following the costal known as the radial, and the other preceding the cubital. The branches of these compound veins are known as nervules. The nervules of the radial veins branch upwardly and outwardly toward the costal margin and the apex of the fore-wing. There are usually four to five radial nervules. In the hind-wing the radial is simple. The median veins of the hindwing has three nervules as in the fore-wing. Toward the base in both wings, there are the cells, which may be wholly or partially open at its outer extremity, or closed. The veinlets which close the cell at its outer part are known as the discocellular veins, of which there are normally three.

 

Butterflies generally hold their wings erect when they are at rest, with their two upper surfaces in proximity, the under surfaces alone displaying their colours to the eye. Only in few genera of the larger butterflies, is there an exception to this rule, sace in the case of the Hesperiidae, or "skippers" in which very frequently, while the fore-wings are folded together, the hind-wings lie in a horizontal position.

 

Reproduction system of the adult and the external genitalia

The abdomen has ten segments, although the posterior ones are indistinct. Each of the first eight segments bears a pair of spiracles. The first or second segments bear paired auditory organs in the pyralid and geometrid moths. Segmental appendages are absent except for vestiges that may form parts of the genitalia. Various segments may bear special structures that produce and disperse pheromones. The genitalia of both sexes are often complex and bear characteristic spines, teeth, setae, and scale tufts. These structures are important in complex courtships and matings, preventing hybridization between unsuitable males and females. In males a ringlike structure (vinculum) is the base of attachment for a number of dorsal structures (tegumen, uncus, and gnathos) and a pair of lateral clasping organs (valvae). In copulation a median, tubular organ (the aedeagus) is extended through an eversible sheath (vesica) to inseminate the female. These structures evolutionarily derive from the body-wall plates, or sclerites (lateral tergites and ventral sternites), of segments eight and 10 and from vestiges of abdominal appendages. The female genitalia exhibit a number of different patterns of the internal ducts and the openings, varying from a condition in which there are no special genital openings, insemination and egglaying (oviposition) taking place through a single aperture, shared with the excretory system, to one in which there are two specialized openings, one for insemination and one for oviposition, both distinct from the anus.

The internal reproductive systems of both sexes contain the organs typical of most insects. The testes of the male are paired in primitive lepidopterans but fused into a single organ in advanced forms. In both cases, the sperm ducts are paired. As in other insects, the sperm pass from the testes down paired ducts (vasa deferentia) for storage in sacs called seminal vesicles. Accessory glands, providing fluids that lengthen the life of the sperm, open into the vasa deferentia.

The female reproductive system consists of paired ovaries, paired accessory glands that provide the yolks and shells of the eggs, and a system of receptacles and ducts for receiving, conducting, and storing sperm. The individual oviducts join to form a common oviduct that leads to the vagina. In copulation, the male deposits a sperm capsule (spermatophore) in a receptacle (bursa copulatrix) of the female. The spermatophore releases the sperm, which swim into the oviduct and thence to the seminal receptacle (bulla seminalis) where they are stored until egg laying, which may be hours, days, or months after mating. Back to the Contents

 

Ecology Back to the Contents

Behaviour Back to the Contents

 

 

Food selection by the adult

Adults locate their food sources by both sight and scent, the former being especially important in the diurnal species, the latter in many diurnal species and in the nocturnal ones. The chief source is floral nectar, but sap (especially if fermenting), overripe fruits, homopteran honeydew, fecal matter, and carrion are sometimes used, usually by special groups. There are mutualistic relationships of a broad sort between the species of Lepidoptera with flower-visiting adults and the plants whose flowers they visit and pollenate, but these are seldom specific or obligate, since only rarely are the plant and the lepidopteran mutually dependent. Exceptions are some members of the orchid and morning glory families with very deep, tubular flowers. These appear to be pollinated only by certain hawkmoths with very long proboscises ("tongues"). The mutualism of the yucca moths (Prodoxidae) and yucca plants is obligate; the moth larvae feed only in yucca fruits and the latter can develop only from moth-pollinated flowers. The female yucca moth has special tentacles on the first maxillae, with which it gathers and carries balls of pollen. Back to the Contents

 

 

Migration

Many Lepidoptera are famous migrants. The American monarch butterfly (Danaus plexippus) is the only species known to perform an annual two-way migration, the same individuals flying southward in the autumn and northward in the spring. The species has also crossed the Pacific Ocean, colonizing Hawaii and Australia, and occasionally reaches Africa and Europe. The cosmopolitan painted lady (Cynthia cardui) stages mass flights nearly everywhere it occurs; these are one-way flights with no returns and must be classed as emigrations, rather than true migrations. Many other species in Europe and North America fly northward in large numbers, often reaching regions in which they cannot survive the winters. In Europe the painted lady and many moths reach Britain and Scandinavia from central Europe. In North America the painted lady, the cloudless sulphur butterfly (Phoebis eubule), and many noctuid moths often reach Canada. Many spectacular migrations occur in the tropics, in which swarms numbering many millions may fly out to sea and be lost. The best known species are pierid butterflies, but large migrations of the large diurnal moths Urania leila and Urania fulgens have also been recorded. The usual explanation of such mass population movements i.e., the advantage of possibly extending the range of the species is far from adequate in many such instances. Back to the Contents

 

 

Environmental hazards

As primary consumers of green plant material, the Lepidoptera are enormously important in food chains, not only because of the very large number of species in the order and the diversity of their food habits, but also because of the abundance of individuals. In most land environments they, in turn, are eaten by a host of other animals: predators, parasites, and scavengers. All stages in their life cycles are thus under continual attack.

The major invertebrate predators on Lepidoptera include centipedes, spiders, mantids, bugs, ground beetles, ants, and both social and solitary wasps. Important predators among vertebrates include toads and tree frogs, lizards, birds, rodents, bats, and monkeys. Some of the invertebrates locate their prey by scent, others by sight; most of the vertebrates hunt by sight, except for the bats, which hunt by acoustic echolocation (the so-called bat "sonar").

The chief groups of parasites that attack Lepidoptera are tachinid flies (Tachinidae) and many families of wasps, chiefly of the Ichneumonoidea, Chalcidoidea, and Cynipoidea. More precisely called parasitoid predators, they are probably more important than the direct predators. The female parasitoids locate suitable hosts, chiefly by scent, and lay their eggs in, on, or near them. The parasitoid larvae live inside their hosts, gradually feeding on the host tissues and almost invariably consuming them almost completely. Lepidoptera seem to have evolved few defenses against parasitoids, unless some of their toxic or repellent secretions serve to discourage them. The high reproductive rate is important as a counter against loss to parasitoids, as well as against other adverse factors.

Small, red trombiculid mites often ride about on adult Lepidoptera, probably doing them no harm. A few other mites, however e.g., Myrmonyssus--live and breed in the tympanic cavities of noctuid moths, destroying their auditory structures. Curiously, they regularly settle in only one of a moth's two tympanic cavities and thus only half deafen it. It is believed that, by leaving the moth with one good ear, the mite reduces the likelihood of the moth (and hence the mite itself) being captured and eaten by a bat. Lepidoptera are subject to attack by a considerable number of protozoa, roundworms, bacteria, viruses, and fungi that affect the larvae chiefly during peaks of abundance and crowding. Some of these organisms have been used by man as a means of controlling injurious species. Back to the Contents

 

 

 

Protection against danger

It is chiefly against the sight-hunting predators that the Lepidoptera have evolved a multiplicity of defense mechanisms that are unequalled by those of any other group of animals. The adults of many groups, such as skippers, many butterflies, hawk moths and many underwing moths, have fast erratic flight. When escaping they dart or fall to cover and often remain immobile for some time. They have a good chance of escaping, especially if they are coloured like their surroundings. Larvae, especially when small, drop suddenly when disturbed, either dangling from a silk thread or falling to concealment on the ground. The larvae of some noctuids can jump several inches. Dense, loose hairs and scales make many moths slippery and may facilitate escape from sticky spider webs.

Certain noctuid moths and possibly some geometrids and pyralids, subject to predation by bats, are able to receive and identify the navigational sound pulses of the bats. Upon hearing bat pulses, these moths perform violent evasive flight movements (when the bat sound is loud, hence close) or dive to the ground (when the bat pulse is weaker, indicating that the danger is further away).

Targets, such as prominent colour spots or tails on the hindwings, attract the attention and focus the attacks of predators onto parts of the prey less vulnerable to injury. Such spots are likely to be seized and torn off, but this does the moth or butterfly no real harm and gives it time to escape without vital injury.

Many species manage to hide very effectively from predators. Many cutworms (Noctuidae) and other larvae hide in litter by day, feeding only at night. Many moths hide in crevices, often under loose bark, and some seem to have especially flattened bodies for this purpose. Hibernating butterflies spend the winter in hollow trees or hanging immobile among dead leaves. The larvae of a great many moths, of most skippers and of many butterflies, live in individual nests of rolled, folded, or webbed leaves or grass. Sod webworms live in silk-lined tunnels in turf. Wood borers, especially those in rootstocks and deep tunnels, are relatively secure. Many larvae aggregate in communal nests such as those of the tent caterpillars (Malacosoma), the larvae of the ermine moth (Yponomeuta), and those of the Mexican social white butterfly (Eucheira socialis). The larvae of the bagworms (Psychidae) and casebearers (Coleophoridae) live and pupate in individual, portable cases that are often masked with bits of leaf or twig. Some larvae, such as those of the green geometrid moths (Synchlora), attach bits of leaves or flower petals to themselves. Cocoons are frequently masked with leaves or debris; those of the puss moths and some dagger moths (Apatela) are hard, woody, and inconspicuous.

A cryptic (camouflaged) appearance conceals something only in appropriate surroundings, and only when accompanied by proper behaviour, usually immobility. Great numbers of larval, pupal, and adult Lepidoptera are thus protected in their natural environments, chiefly on or about plants. Leaf-eating larvae usually blend into leafy environments. Many caterpillars (e.g., Sphingidae, Geometridae) have stripes that simulate leaf veins. The sawtoothed elm caterpillar (Nerice) has a jagged outline resembling the edge of an elm leaf. A great many measuring worms (Geometridae) are notably twiglike, with long, slender, stiffly held bodies. Many other caterpillars, especially Notodontidae, have irregular shapes that resemble twisted dead leaves. Likewise, many adult moths that rest during the day among leaves or on bark are cryptically coloured and patterned; moreover, their behavioral mechanisms lead them to select matching backgrounds on which to rest. Many larvae and adults are disruptively marked; i.e., have bold, contrasting patches or bands of colour that "break up" their outlines into two or more seemingly unrelated masses. Many adult moths and butterflies have "flash coloration," which serves to startle, and thus to delay momentarily, an attacker. Moths with cryptic forewings, and butterflies with cryptic undersides, show only these surfaces when they are at rest. If, when disturbed, they suddenly expose brilliantly coloured and marked hindwings, such as in underwing moths (Catocala), or upper surfaces (for example, morpho, hairstreak, and anglewing butterflies), the effect is startling. When the animal lands, the bright surfaces are suddenly hidden, causing it to "disappear." A similar "startle" effect protects larvae that have prominent spots simulating large eyes.

Startling sounds are produced by members of many groups. Larvae of hawkmoths (Sphingidae) and the pupae of many lycaenid butterflies make squeaking or grating sounds when disturbed. The adult death's head moth (Acherontia atropos) makes a loud chirping sound. Ageronia butterflies (Argynnidae (=Nymphalidae)), when startled into flight, make a loud, clicking sound by means of a structure on the wings. This may have a startling, and therefore a delaying, effect on a predator. Certain butterflies and moths possess repellent or toxic substances that provide protection against predators.

Sometimes these are secured directly from the plant on which the larva feeds, such as the toxins (glycosides) that occur in high concentration in many milkweeds eaten by danaid butterflies. More often, the toxin is secreted by the insect itself. The toxin often occurs generally in the blood (e.g., hydrogen cyanide in zygaenid moths) or in the gut, or may be the product of special glands, which release it at the time of an attack. Tiger moths (Arctiidae) give off bubbling drops of repellent from glands on the prothorax. Many groups show autohemorrhization, or reflex bleeding, from leg and body joints when disturbed. The larvae of swallowtail butterflies (Papilio) and tussock moths (Lymantriidae) give off strong smelling, volatile substances from extrusible scent organs (osmeteria). Many notodontid moth larvae spray formic acid from ventral prothoracic glands. Many larvae and some adults introduce toxins that cause severely painful nettling effects by means of hollow, barbed hairs; the slug caterpillar moths (Eucleidae), flannel moths (Megalopygidae), io moths (Saturniidae), and some liparid moths are noted for this. A few adult moths (e.g., Arctia caja, some Sphingidae) inject toxins through sharp spines on their hind legs. Besides those already mentioned, the chief groups that are chemically protected are the moth families Ctenuchidae, Pericopidae, and Dioptidae and the butterfly groups Heliconiinae, Ithomiinae, Acraeinae, and the swallowtails (Battus) that feed on birthwort. The great majority of these and other protected forms are aposematic; i.e., have markings, shapes, and behaviour that draw attention. They are thus easily recognized and remembered by predators which, after seizing only one or two individuals, will thereafter leave other similar ones alone.

The protective advantage gained by a distasteful or dangerous insect and accompanied by aposematic coloration or acoustic warning may be utilized by harmless and edible insects, through the evolution of close resemblances, known as mimicry. The distasteful insect, known as the model, may even be a member of an insect order different from that of the mimic. Members of various lepidopteran families mimic wasps, bees, and beetles. The clearwing moths (Sesiidae) are particularly effective mimics of certain stinging wasps, the resemblance being carried to details of the shape and coloration of the wings, abdomen, and legs. Mimicry occurs widely in the moth families Dioptidae, Chalcosiidae, Callidulidae, and Zygaenidae and in the butterfly families Argynnidae (=Nymphalidae), Papilionidae, Pieridae, and Riodinidae.

Not all warning mechanisms are visual. Inedible arctiid and pericopid moths make high-pitched grating sounds by means of timbal (drumlike) organs. These sounds, above the frequency range audible to man, but within that audible to bats, may function to warn the bat of the moth's inedibility, avoiding capture and tasting that would be injurious to the moth. Some authorities believe that these sounds may interfere with the bats' acoustic orientation system, preventing the detection of the moth.

The occurrence in a population of two or more distinct hereditary variants, or morphs, is known in many Lepidoptera. Each morph may have a different adaptive value, linked with such physiological features as resistance to cold, or to toxins in the environment. Striking variation in appearance may have great adaptive value by confusing predators, making it more difficult to learn the appearance of the prey. Mixed populations of both light and dark (melanic) individuals may survive better in mixed light and dark environments, and actually be prepared for a shift of the environment to a predominance of dark, through the normal succession of forest growth or through man-made industrial pollution. In England investigations of the peppered moth Biston betularia have abundantly documented the evolution of "industrial" and "natural" melanism and shown major genetic population changes taking place very rapidly.

Striking polymorphisms occur in some mimetic species, notably the African swallowtail, Papilio dardanus. The occurrence of different species of inedible butterflies ("models") in various regions has been accompanied by the evolution of correspondingly different mimetic females of the single species of swallowtail. The North American tiger swallowtail, P. glaucus, has mostly black females where it coexists with the black distasteful pipevine swallowtail, Battus philenor. Where B. philenor does not occur, however, the P. glaucus females tend to be all nonmimetic yellow like the males, black having no protective significance. Some very striking mimetic polymorphisms occur among Neotropical Heliconius butterflies and their various models and mimics. Back to the Contents  

 

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Introduction to the Entomology Unit II : Classification 

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