CHAPTER VIII

INSECTS

THE GRASSHOPPER

SUGGESTIONS.--Collect grasshoppers, both young and full-grown, and keep alive in broad bottles or tumblers and feed on fresh grass or lettuce. When handling a live grasshopper, never hold it by its legs, as the joints are weak. To keep them for some time and observe their molts, place sod in the bottom of a box and cover the box with mosquito netting or wire gauze.

What is the =general shape= of its body? (Fig. 106.) Where is the body thickest? Is it bilaterally symmetrical, that is, are the two sides of the body alike? Is the _skeleton_, or hard part of the body, internal or external? Is the skeleton as stiff and thick as that of a crawfish? What is the length of your specimen? Its color? Why does it have this coloration? In what ways does the grasshopper resemble the crawfish? Differ from it?

[Illustration: FIG. 106.--A GRASSHOPPER.]

=The Three Regions of the Body.=--The body of the grasshopper is divided into three regions,--the _head_, _thorax_, and _abdomen_. Which of these three divisions has no distinct subdivisions? The body of the grasshopper, like that of the earthworm, is made of _ringlike segments_. Are the segments most distinct in the head, thorax, or abdomen? Which region is longest? Shortest? Strongest? Why? Which region bears the chief sense organs? The appendages for taking food? The locomotory appendages? Which division of the body is most active in breathing?

=The Abdomen.=--About how many segments or rings in the abdomen? Do all grasshoppers have the same number of rings? (Answer for different species and different individuals of the same species.) The first segment and the last two are incomplete rings. Does the flexibility of the abdomen reside in the rings, or the joints between the rings? Is there merely a thin, soft line between the rings, or is there a fold of the covering? Does one ring slip into the ring before it or behind it when the abdomen is bent?

As the grasshopper =breathes=, does each ring enlarge and diminish in size? Each _ring is divided into two parts_ by folds. Does the upper half-ring overlap the lower half-ring, or the reverse? With magnifying glass, find a small slit, called a _spiracle_, or breathing hole, on each side of each ring just above the side groove (Fig. 106). A tube leads from each spiracle. While the air is being taken in, do the two portions of the rings move farther apart? When they are brought together again, what must be the effect? In pumping the air, the abdomen may be said to work like a bellows. Bellows usually have folds to allow motion. Is the comparison correct?

How many times in a minute does the grasshopper take in air? If it is made to hop vigorously around the room and the breathing is again timed, is there any change?

[Illustration: FIG. 107.--A GRASSHOPPER DISSECTED.]

Find the =ears= on the front wall of the _first abdominal ring_ (Fig. 107). They may be seen by slightly pressing the abdomen so as to widen the chink between it and the thorax. The ears are merely glistening, transparent _membranes_, oval in form. A _nerve_ leads from the inner surface of each membrane. State any advantage or disadvantage in having the ears located where they are.

=Ovipositor.=--If the specimen is a female, it has an egg-placer or ovipositor, consisting of _four blunt projections_ at the end of the abdomen (Fig. 107). If it is a male, there are only two appendages. These are above the end of the abdomen, and smaller than the parts of the ovipositor. Females are larger and more abundant than males. In laying the eggs, the four blunt points are brought tightly together and then forced into the ground and opened (Fig. 108). By repeating this, a pit is made almost as deep as the abdomen is long. What sex is shown in Fig. 106? Fig. 107?

=Draw= a side view of the grasshopper.

[Illustration: FIG. 108.--GRASSHOPPER LAYING EGGS. (Riley.)]

=Thorax.=--This, the middle portion of the body, consists of _three segments_ or rings (Fig. 107). Is the division between the rings most apparent above or below? Which two of the three rings are more closely united?

The front ring (_prothorax_) of the thorax has no rings. Is it larger above or below? Does it look more like a collar or a cape? (Fig. 106.) A spiracle is found on the second ring (_mesothorax_, or middle thorax) just above the second pair of legs. There is another in the soft skin between the prothorax and mesothorax just under the large cape or collar. The last ring of the thorax is called the _metathorax_ (rear thorax).

How many =legs= are attached to each ring of the thorax? Can a grasshopper walk? Run? Climb? Jump? Fly? Do any of the legs set forward? (See Fig. 106.) Outward? Backward? Can you give reasons for the position of each pair? (Suggestion: What is the use of each pair?) If an organ is modified so that it is suited to serve some particular purpose or function, it is said to be _specialized_. Are any of the legs specialized so that they serve for a different purpose than the other legs?

The leg of a grasshopper (as of all insects) is said to have _five parts_, all the small parts after the first four parts being counted as one part and called the foot. Are all the legs similar, that is, do the short and long joints in all come in the same order? Numbered in order from the body, which joint of the leg is the largest,--the first, second, third, or fourth? Which joint is the shortest? The slenderest? Which joint has a number of sharp points or spines on it? Find by experiment whether these spines are of use in walking (Fig. 106). Jumping? Climbing? In what order are the legs used in walking? How many legs support the body at each step?

[Illustration: FIG. 109.--HOW A GRASSHOPPER WALKS.]

[Illustration: FIG. 110.--HOW A SPIDER WALKS.]

All animals that have ears have ways of communicating by =sounds=. Why would it be impossible for the grasshopper to have a _voice_, even if it had vocal cords in its throat? The male grasshoppers of many species make a =chirping=, or stridulation, by rubbing the wing against the leg. Look on the inner side (why not outer side?) of the largest joint of the hind leg for a _row of small spines_ visible with the aid of a hand lens (Fig. 111). The sound is produced by the outer wings rubbing against the spines. Have you noticed whether the sound is produced while the insect is still or in motion? Why? The male grasshoppers of some species, instead of having spines, rub the under side of the front wing on the upper side of the hind wing.

[Illustration: FIG. 111.--_A_, ROW OF SPINES, _z_, used in chirping.

_B_, the same more enlarged.]

=Wings.=--To what is the first pair of wings attached? The second pair? Why are the wings not attached to the prothorax? Why are the wings attached so near the dorsal line of the body? Why are the second and third rings of the thorax more solidly joined than the first and second rings?

Compare the first and second pairs of wings in shape, size, color, thickness, and use (Fig. 112). How are the second wings folded so as to go under the first wings? About how many folds in each?

[Illustration: FIG. 112.--GRASSHOPPER IN FLIGHT.]

=Draw= a hind wing opened out.

=Head.=--What is the shape of the head viewed from the front, the side, and above? _Make sketches._ What can you say of a neck? Is the head movable in all directions?

What is the position of the large =eyes=? Like the eyes of the crawfish, they are _compound, with many facets_. But the grasshopper has also _three simple eyes_, situated one in the middle of the forehead and one just above each antenna. They are too small to be seen without a hand lens. How does the grasshopper’s range of vision compare with that of the crawfish?

Are the =antennæ= flexible? What is their shape? Position? Are they segmented? Touch an antenna, a wing, a leg, and the abdomen in succession. Which seems to be the most sensitive to touch? The antennæ are for feeling; in some species of insects they are also the organs of hearing.

[Illustration: FIG. 113.]

The =mouth parts= of a grasshopper are highly specialized. They should be compared with the mouth parts of a beetle shown in Fig. 113, since the mouth parts of these two insects correspond closely. If the grasshopper is fed with a blade of fresh grass, the function of each mouth part may be plainly seen. It is almost impossible to understand these functions by studying a dead specimen, but a fresh specimen is much better than a dry one.

[Illustration: FIG. 114.--_a_, FOOD TUBE OF BEETLE.

_b_, gizzard; _d_, intestine; _c_, biliary vessels. See Fig. 127.]

The upper lip, or _labrum_, is seen in front. Is it tapering or expanded? In what direction is it movable? The dark pointed biting jaws (_mandibles_) are next. Are they curved or straight? Sharp or blunt pointed? Notched or smooth? Do they work up and down, or sideways? The holding jaws (_maxillæ_), each with two jaw fingers (_maxillary palpi_) are behind the chewing jaws. Why? The lower lip (_labium_) has a pair of lip fingers (_labial palpi_) upon it. The brown tongue, usually bathed in saliva, is seen in the lower part of the mouth. Since the grasshopper has no lips, or any way of producing suction, it must lap the dew in drinking. Does it merely break off bits of a grass blade, or does it chew?

The heart, circulation, nervous system, digestive and respiratory organs of the grasshopper agree mainly with the general description of the organs of insects given in the next section.

=Microscopic Objects.=--These may be bought ready mounted, or may be examined fresh. A portion of the covering of the large eye may be cut off and the dark layer on the inside of the covering scraped off to make it transparent. What is the shape of the facets? Can you make any estimate of their number? A portion of the transparent hind wing may be used, and the “veins” in it studied. A thin bit of an abdominal segment containing a spiracle will show the structure of these important organs.

[Illustration: FIG. 115.--EGG AND MOLTS OF A GRASSHOPPER.]

=Growth of the Grasshopper.=--Some species hibernate in sheltered places and lay eggs in the spring, but adult species are scarce at that season. Most species lay the eggs in the fall; these withstand the cold and hatch out in the spring. Those hatched from one set of eggs sometimes stay together for a few days. They eat voraciously, and as they grow, the soft skin becomes hardened by the deposit of horny substance called chitin. This prevents further growth until the insect molts, the skin first splitting above the prothorax. After hatching, there are five successive periods of growth. At which molt do the very short wings first appear? (Fig. 115.) After the last molt the animal is complete, and changes no more in size for the rest of its life. There has been an attempt among writers to restrict the term grasshopper to the long-winged, slender species, and to call the shorter winged, stouter species locusts according to old English usage.

[Illustration: FIG. 116.--COCKROACH.]

[Illustration: FIG. 117.--PRAYING MANTIS, or devil’s horse.]

[Illustration: FIG. 118.--CRICKET.]

[Illustration: FIG. 119.--MOLE CRICKET.]

=Economic Importance of Grasshoppers.=--Great injury is often done to vegetation by grasshoppers; however, the millions of tiny but ravenous eaters hatched in early spring are usually soon thinned out by the birds. The migratory locusts constitute a plague when they appear, and they have done so since ancient times. The Rocky Mountain locusts flying eastward have darkened the sky, and where they settled to the earth ate almost every green thing. In 1874-5 they produced almost a famine in Kansas, Nebraska, and other Western states. The young hatched away from the mountains were not healthy, and died prematurely, and their devastations came to an end. Of course the migrations may occur again. Packard calculates that the farmers of the West lost $200,000,000 because of their ravages in 1874-5.

[Illustration: FIG. 120.--FRONT LEG OF MOLE CRICKET. × 3.]

The _cockroaches_ (Fig. 116), =kindred of the grasshoppers=, are household pests that have migrated almost everywhere that ships go. The _praying mantis_ (Fig. 117), or _devil’s horse_, also belongs to this order. It is beneficial, since it destroys other insects. Which of its legs are specialized? The _walking stick_ (Fig. 121) and _cricket_ (Fig. 118), like most members of the order, are vegetarian.

[Illustration: FIG. 121.--FOUR WALKING STICK INSECTS.]

Are grasshoppers more common in fields and meadows, or in wooded places? How many different colors have you seen on grasshoppers? Which colors are most common?

Grasshoppers are very scarce in Europe as they love dry, warm countries. Why do locusts migrate? Give an instance in ancient times.

How long do most grasshoppers live? Does a grasshopper spread its wings before it flies? Does it jump and fly together? Can it select the place for alighting?

NOTE TO TEACHER.--=Field work in Zoology= should be systematic. Every trip has a definite region and definite line of study in view, but every animal seen should be noted. The habitat, adaptation by structure and habits to the environment, relations to other animals, classification of animals seen, should be some of the ideas guiding the study. The excursions may be divided somewhat as follows, according as opportunities offer: Upland woods, lowland woods, upland pastures, fields, swamps, a fresh-water lake, a pond, lower sea beach, higher sea beach, sand hills along shore, roadside, garden, haunts of birds, insect visits to flowers, ground insects, insects in logs.

An alphabetical letter file may be used for filing individual field observations. These should be placed before the class orally or in writing. If accepted as reliable (repeated and revised if necessary), the observations should be filed away and credit given the student on a regular scale. Thus will grading and marks be placed to encourage intelligent study of nature rather than book or laboratory cram. One per cent to be added to the final grade may be credited for every species of pupa, every rare insect (with an observed fact as to its habits) brought in, every bird migration observed, every instance of protective coloration, mimicry (p. 146), outwitting of enemy, instance of injurious insects, and how to combat them, etc. Sharp eyes and clear reasoning will then count as much on school grades as a memory for words or mechanical following of laboratory directions. On scale of 100, class work = 50, examination = 25, field work = 25.

=Collecting Insects.=--In cities and towns insects, varying with the season, are attracted by electric lights. Beetles and bugs will be found under the lights, moths on posts near the lights, grasshoppers and crickets and other insects in the grass near by. A lamp placed by a window brings many specimens. In the woods and in rocky places insects are found under logs and stones, and under the bark of dead trees. In open places, prairies, meadows, and old fields with grass and flowers, it will be easy to find grasshoppers, butterflies, and some beetles. Ponds and streams are usually rich in animal forms, such as bugs and beetles, which swim on or under the surface, and larvæ of dragon flies crawling on the bottom. Dragon flies and other insects that lay eggs on the water are found flying in the air above. (In the spring, newly hatched crawfish, tadpoles, and the eggs of frogs and toads should also be collected, if found.) Moths may be caught at night by daubing molasses or sirup made from brown sugar upon the trunks of several trees, and visiting the trees at intervals with a lantern.

An insect net for catching butterflies and for dredging ponds may be made by bending a stout wire into a circle one foot in diameter, leaving enough straight wire to fasten with staples on an old broomstick. To the frame is fastened a flour sack, or cone made of a piece of mosquito netting.

Butterflies and moths should be promptly killed, or they will beat their wings to pieces. The quickest method is by dropping several drops of gasoline upon the ventral (under) side of the thorax and abdomen. (Caution: Gasoline should never be used near an open fire, or lamp, as explosions and deaths result from the flame being led through the gasoline-saturated air to the vessel containing it.)

A cigar box and a bottle with a notched cork may be used for holding specimens. Cigar boxes may be used for holding collections of dried insects. Cork or ribbed packing paper may be fixed in the bottom for supporting the insect pins. Moth balls or tobacco may be placed in each box to keep out the insect pests which infest collections.

It is pleasant and profitable to take to the fields a small book like this one, or even Comstock’s “Manual of Insects,” or Kellogg’s “American Insects,” and study the insects and their habits where they are found.

Captured insects which, in either the larval or perfect stage, are injurious to vegetation, should always be killed after studying their actions and external features, even if the internal structure is not to be studied. Beneficial insects, such as ladybugs, ichneumon flies, bees, mantis (devil’s horse), dragon flies, etc., should be set free uninjured.

ANATOMY AND GENERAL CHARACTERISTICS OF THE CLASS INSECTA

The =body= of an insect (_e.g._ a wasp, Fig. 122) is divided by means of two marked narrowings into three parts: the head (_K_), chest (_B_), and abdomen (_H_).

[Illustration: FIG. 122.--A WASP.]

The =head= is a freely movable capsule bearing four pairs of appendages. Hence it is regarded as having been formed by the union of four rings, since the _ancestor of the insects_ is believed to have consisted of similar rings, each ring bearing a pair of unspecialized legs. The early grub or caterpillar stage of insects is believed to resemble somewhat the ancestral form.

The typical =mouth parts= of an insect (Fig. 123), named in order from above, are (1) an upper lip (labrum, _ol_) (2) a pair of biting jaws (mandibles, _ok_) (3) a pair of grasping jaws (maxillæ, _A_, _B_), and (4) a lower lip (labium, _m_, _a_, _b_). The grasping jaws bear two pairs of jointed jaw fingers (maxillary palpi, _D_, _C_), and the lower lip bears a pair of similar lip fingers (labial palpi, _d_). The biting jaws move sideways; they usually have several pointed notches which serve as teeth. Why should the grasping jaws be beneath the chewing jaws? Why is it better for the lower lip to have fingers than the upper lip? Why are the fingers (or palpi) jointed? (Watch a grasshopper or beetle eating.) Why does an insect need grasping jaws?

[Illustration: FIG. 123.--MOUTH PARTS OF BEETLE.]

[Illustration: FIG. 124.--EXTERNAL PARTS OF A BEETLE.]

The chest, or =thorax=, consists of three rings (Fig. 124) called the front thorax (prothorax), middle thorax (mesothorax) and hind thorax (metathorax), or first, second, and third rings. The first ring bears the first pair of legs, the second ring bears the second pair of legs and the upper or front wings, and the third ring bears the third pair of legs and the under or hind wings.

[Illustration: FIG. 125.--LEG OF INSECT.]

The =six feet= of insects are characteristic of them, since no other animals have that number, the spider having eight, the crawfish and crabs having ten, the centipedes still more, while the birds and beasts have less than six. Hence the insects are sometimes called the Six-Footed class (_Hexapoda_). The insects are the only animals that have the =body in three divisions=. Man, beasts, and birds have only two divisions (head and trunk); worms are not divided.

=Define= the class _insecta_ by the two facts characteristic of them (_i.e._ possessed by them alone), viz.: Insects are animals with ____ and ____. Why would it be ambiguous to include “hard outer skeleton” in this definition? To include “bilateral symmetry”? “Segmented body”? The definition of a class must _include_ all the individuals of the class, and _exclude_ all the animals that do not belong to the class.

The leg of an insect (Fig. 125) has five joints (two short joints, two long, and the foot). Named in order from above, they are (1) the hip (coxa), (2) thigh ring (trochanter), (3) thigh (femur), (4) the shin (tibia), (5) the foot, which has five parts. Which of the five joints of a wasp’s leg (Fig. 122) is thickest? Slenderest? Shortest? One joint (which?) of the foot (Fig. 122) is about as long as the other four joints of the foot combined. Is the relative length of the joints of the leg the same in grasshoppers, beetles, etc., as in the wasp (Figs.)? Figure 125 is a diagram of an insect’s leg cut lengthwise. The leg consists of thick-walled tubes (_o_, _n_) with their ends held together by thin, easy-wrinkling membranes which serve as joints. Thus motion is provided for at the expense of strength. When handling live insects they should never be held by the legs, as the legs come off very easily. Does the joint motion of insects most resemble the motion of hinge joints or ball-and-socket joints? Answer by tests of living insects. There are no muscles in the foot of an insect. The claw is moved by a muscle (_m_) in the thigh with which it is connected by the long tendon (_z_, _s_, _t_, _v_). In which part are the breathing muscles? As the wings are developed from folds of the dorsal skin, the wing has two layers, an upper and a lower layer. These inclose the so-called “nerves” or ribs of the wing, each of which consists of a blood tube inclosed in an air tube.

[Illustration: FIG. 126.--FOOT OF FLY, with climbing pads.]

The =abdomen= in various species consists of from five to eleven overlapping rings with their foldlike joints between them. Does each ring overlap the ring in front or the one behind it?

The =food tube= (Fig. 127) begins at the mouth, which usually contains salivary glands (4, Fig. 127). What is the color of the grasshopper’s saliva? The food tube expands first into a _croplike_ enlargement; next to this is the _stomach_ (6, Fig. 127), which resembles the gizzard in birds, as its inner wall is furnished with chitinous teeth (_b_, Fig. 114). These reduce the food fragments that were imperfectly broken up by the biting jaws before swallowing. _Glands_ comparable to the liver of higher animals open into the food tube where the stomach joins the small intestine. At the junction of the small and large intestine (9) are a number of _fine tubes_ (8) which correspond to kidneys and empty their secretion into the large intestine.

[Illustration: FIG. 127.--VISCERA OF GRASSHOPPER. Key in text. Compare with Fig. 114.]

[Illustration: FIG. 128.--AIR TUBES OF INSECT.]

The =breathing organs= of the insects are peculiar to them (see Fig. 128). They consist of tubes which are kept open by having in their walls continuous spirals of horny material called _chitin_. Most noticeable are the two large membranous tubes filled with air and situated on each side of the body. Do these tubes extend through the thorax? (Fig. 128.) The air reaches these two main tubes by a number of pairs of short windpipes, or _tracheas_, which begin at openings (_spiracles_). In which division are the spiracles most numerous? (Fig. 128.) Which division is without spiracles? Could an insect be drowned, _i.e._ smothered, by holding its body under water? Could it be drowned by immersing all of it but its head? The motion of the air through the breathing tubes is caused by a bellowslike _motion of the abdomen_. This is readily observed in grasshoppers, beetles, and wasps. As each ring slips into the ring in front of it, the abdomen is shortened, and the impure air, laden with carbon dioxid, is forced out. As the rings slip out, the abdomen is extended and the fresh air comes in, bringing oxygen.

[Illustration: FIG. 129.--INSECT’S HEART (plan).]

[Illustration: FIG. 130.--DIAGRAMS OF EVOLUTION OF PERICARDIAL SAC around insect’s heart from a number of veins (Lankester).]

[Illustration: FIG. 131.--POSITION OF INSECT’S HEART, food tube, and nerve chain.]

=The Circulation.=--Near the dorsal surface of the abdomen (Fig. 131) extends the long, slender _heart_ (Fig. 129). The heart has divisions separated by valvelike partitions. The blood comes into each of the heart compartments through a pair of openings. The heart contracts from the rear toward the front, driving the blood forward. The blood contains bodies corresponding to the _white corpuscles_ of human blood, but lacks the red corpuscles and the red color. The blood is sent even to the wings. The _ribs_ on the wings consist of blood tubes inclosed in air tubes, so that the blood vessels are surrounded by air, and the purification of the blood is taking place throughout the course of the circulation. Hence the imperfect circulation is no disadvantage. The perfect provision for supplying oxygen explains the remarkable activity of which insects are capable and their great strength, which, considering their size, is unequaled by any other animals.

[Illustration: FIG. 132.--NERVOUS SYSTEM OF BEE.]

=The Nervous System.=--The heart in backboned animals, e.g. man, is ventral and the chief nerve trunk is dorsal. As already stated, the heart of an insect is dorsal; its chief nerve chain, consisting of a _double row of ganglia_, is near the ventral surface (Fig. 131). All the ganglia are below the food tube except the first pair in the head, which are above the gullet. This pair may be said to correspond somewhat to the brain of backboned animals; the nerves from the eyes and feelers lead to it. With social insects, as bees and ants, it is large and complex (Fig. 132). In a typical insect they are the largest ganglia.

[Illustration: FIG. 133.--FEELER of a beetle.]

=The Senses.=--The sense of _smell_ of most insects is believed to be located in the feelers. The organ of _hearing_ is variously located in different insects. Where is it in the grasshopper? The organs of _sight_ are highly developed, and consist of two compound eyes on the side of the head and three simple eyes on the top or front of the head between the compound eyes. The simple eye has nerve cells, pigments, and a lens resembling the lens in the eyes of vertebrates (Fig. 134). The compound eye (Fig. 135) has thousands of facets, usually hexagonal, on its surface, the facets being the outer ends of cones which have their inner ends directed toward the center of the eye. It is probable that the large, or compound, eyes of insects only serve to distinguish bright objects from dark objects. The simple eyes afford distinct images of objects within a few inches of the eye. In general, the sight of insects, contrary to what its complex sight organs would lead us to expect, is not at all keen. Yet an insect can fly through a forest without striking a twig or branch. Is it better for the eyes that are immovable in the head to be large or small? Which has comparatively larger eyes, an insect or a beast?

[Illustration: FIG. 134.--Diagram of simple eye of insect.

_L_, lens; _N_, optic nerve.]

[Illustration: FIG. 135.--COMPOUND EYE OF INSECT.

1, hexagonal facets of crystalline cones. 6, blood vessel in optic nerve.]

=Inherited Habit, or Instinct.=--Insects and other animals inherit from their parents their particular form of body and of organs which perform the different functions. For example, they inherit a nervous system with a structure similar to that of their parents, and hence with a tendency to repeat similar impulses and acts. Repeated acts constitute a habit, and _an inherited habit is called an instinct_. Moths, for example, are used to finding nectar in the night-blooming flowers, most of which are white. The habit of going to white flowers is transmitted in the structure of the nervous system; so we say that moths have an instinct to go to white objects; it is sometimes more obscurely expressed by saying they are attracted or drawn thereby.

=Instincts are not Infallible.=--They are trustworthy in only one narrow set of conditions. Now that man makes many fires and lights at night, the instinct just mentioned often causes the death of the moth. The instinct to provide for offspring is necessary to the perpetuation of all but the simplest animals. The dirt dauber, or mud wasp, because of inherited habit, or instinct, makes the cell of the right size, lays the egg, and provides food for offspring that the mother will never see. It seals stung and semiparalyzed spiders in the cell with the egg. If you try the experiment of removing the food before the cell is closed, the insect will bring more spiders; if they are removed again, a third supply will be brought; but if taken out the third time, the mud wasp will usually close the cell without food, and when the egg hatches the grub will starve.

=The Development of Insects.=--The growth and molting of the grasshopper from egg to adult has been studied. All insects do not develop exactly by this plan. Some hatch from the egg in a condition markedly different from the adult. The butterfly’s egg produces a wormlike caterpillar which has no resemblance to the butterfly. After it grows it forms an inclosing case in which it spends a quiet period of development and comes out a butterfly. This change from caterpillar to butterfly is called the _metamorphosis_. The life of an insect is divided into four stages: (1) _egg_, (2) _larva_, (3) _pupa_, and (4) _imago_, or perfect insect (Figs. 136, 137, 138).

[Illustration: FIG. 136.--Measuring worm, the larva of a moth.]

[Illustration: FIG. 137.--Pupa of a mosquito.]

[Illustration: FIG. 138.--THE FOUR STAGES OF A BOTFLY, all enlarged.

_a_, egg on hair of horse (bitten off and swallowed); _b_, larva; _c_, larva with hooks for holding to lining of stomach; _d_, pupal stage, passed in the earth; _e_, adult horse fly.]

The egg stage is one of development, no nourishment being absorbed. The larval stage is one of voracious feeding and rapid growth. In the pupa stage no food is taken and there is no growth in size, but rapid development takes place. In the perfect stage food is eaten, but no growth in size takes place. In this stage the eggs are produced. When there is very little resemblance between the larva and imago, and the pupa is quiescent, the metamorphosis, or change, is said to be _complete_. When, as with the grasshopper, no very marked change takes place between the larva and imago (that is to say, during the pupa stage, which is active), the metamorphosis is said to be incomplete. By studying the illustrations and specimens, and by thinking of your past observations of insects, determine which of the insects in the following list have a complete metamorphosis: beetle, house fly, grasshopper, butterfly, cricket, wasp.

TABLE FOR CLASSIFYING INSECTS (_class Insecta_) INTO ORDERS

ORDER

A₁ =Biting Insects=; mouth parts for grasping and biting

B₁ Wingless; changes (metamorphosis) NO WINGS incomplete (_Aptera_)

B₂ Under wings thinner than upper wings, and FAN WINGS fold like a fan beneath them; changes (_Orthoptera_) incomplete

B₃ Upper wings hard and thick, protecting SHEATH WINGS under wings, which fold both lengthwise and (_Coleoptera_) crosswise beneath them; changes incomplete

B₄ All four wings nearly alike, finely veined, transparent

C₁ Hind wings smaller than fore, two or NERVE WINGS three filaments attached to abdomen, (_Neuroptera_) antennæ long; changes complete

C₂ Hind wings not smaller than fore; no FALSE NERVE WINGS filaments on abdomen, antennæ (_Pseudoneuroptera_) inconspicuous; changes incomplete

A₂ =Sucking Insects=; mouth parts for sucking or licking

B₁ Basal half of upper wing usually leathery, HALF WINGS other half of wing transparent; lower lips (_Hemiptera_) transformed into a tube; true bugs

B₂ Four wings covered by scales, holding-jaws SCALY WINGS (maxillæ) elongated to form a sucking tube (_Lepidoptera_) coiled under head; changes complete

B₃ Four wings, membranous, hind wings hook to JOINED WINGS fore wings in flight; mouth parts for both (_Hymenoptera_) biting and sucking; abdomen with sting; changes complete

B₄ Two wings, mandibles rudimentary, mouth a TWO WINGS soft beak (_Diptera_)

B₅ No wings, mandibles rudimentary, mouth a LOST WINGS horny beak (_Siphonoptera_)

[Illustration: FIG. 139.--MAY FLY. What order (see table)?]

[Illustration: FIG. 140.--SILVER SCALE. (Order?)]

=Exercise in the Use of the Table or Key.=--Write the name of the order after each of the following names of insects:--

Wasp (Fig. 122) Weevil (Fig. 163) Squash bug (Fig. 184) Ant lion (Fig. 170) Dragon fly (Fig. 177) Ichneumon fly (Fig. 159) House fly (Fig. 172) Flea (Fig. 173) Silver scale or earwig (Fig. 140) Codling moth (Fig. 141) Botfly (Fig. 138)

=Moths and Butterflies.=--Order ____? Why ____ (p. 82)?

The presence of scales on the wings is a never-failing test of a moth or butterfly. The wings do not fold at all. They are so large and the legs so weak and delicate that the butterfly keeps its balance with difficulty when walking.

The maxillæ are developed to form the long sucking proboscis. How do they fit together to form a tube? (See Fig. 147.) The proboscis varies from a fraction of an inch in the “miller” to five inches in some tropical moths, which use it to extract nectar from long tubular flowers. When not in use, it is held coiled like a watch spring under the head (Fig. 148). The upper lip (labrum), under lip (labium), and lip fingers (labial palpi) are very small, and the mandibles small or wanting (Fig. 146).

The metamorphosis is complete, the contrast between the caterpillar or larva of the moth and butterfly and the adult form being very great. The caterpillar has the three pairs of jointed legs typical of insects; these are found near the head (Fig. 141). It has also from three to five pairs of fleshy unjointed proplegs, one pair of which is always on the last segment. How many pairs of proplegs has the silkworm caterpillar? (Fig. 143.) The measuring worm, or looper? (Fig. 136.) The pupa has a thin shell. Can you see external signs of the antennæ, wings, and legs in this stage? (Fig. 143.) The pupa is concealed by protective coloration, and is sometimes inclosed in a silken cocoon which was spun by the caterpillar before the last molt. Hairy caterpillars usually produce butterflies, and the naked ones usually produce moths. Hairy ones are uncomfortable for birds to eat. The naked and brightly marked ones (warning coloration) often contain an acrid and distasteful fluid. The injuries from lepidoptera are done in the caterpillar stage. The codling moth (Fig. 141) destroys apples to the value of $6,000,000 annually. The clothes moth (Fig. 171) is a household pest. The tent caterpillar denudes trees of their leaves. The only useful caterpillar is the silkworm (Fig. 143). In Italy and Japan many of the country dwellings have silk rooms where thousands of these caterpillars are fed and tended by women and children. Why is the cabbage butterfly so called? Why can it not eat cabbage? Why does sealing clothes in a paper bag prevent the ravages of the clothes moth?

=Flight of Lepidoptera.=--Which appears to use more exertion to keep afloat, a bird or a butterfly? Explain why. Of all flying insects which would more probably be found highest up mountains? How does the butterfly suddenly change direction of flight? Does it usually fly in a straight or zigzag course? Advantage of this? Why is zigzag flight unnecessary to moths? Bright colors are protective, as lepidoptera are in greatest danger when at rest on flowers. Are the brightest colors on upper or under side of wings of butterfly? Why? (Think of the colors in a flower.) Why is it better for moths to hold their wings flat out when at rest? Where are moths during the day? How can you test whether the color of the wings is given by the scales?

State =how moths and butterflies differ= in respect to: body, wings, feelers, habits; abundance of scales.

=Insects and Flowers.=--We are indebted to insects for the bright colors and sweet honey of flowers. Flowers need insects to carry their pollen to other flowers, as cross-fertilization produces the best seeds. The insects need the nectar of the flowers for food, and the bright colors and sweet odors are the advertisements of the flowers to attract insects. There were no flowers in the world before flying insects were developed. Moths, butterflies, and bees carry most pollen (see Plant Biology, Chap. VI).

=Comparative Study.=--Make a table like this, occupying entire page of notebook, leaving no margins, and fill in accurately:--

==========+=========+=========+=========+=========+=========+========= | | | FLY | DRAGON | BEETLE | BEE | GRASS- | BUTTER- | pp. 92, | FLY, | pp. 90, | pp. 88, | HOPPER | FLY | 93 | p. 93 | 91 | 89 ----------+---------+---------+---------+---------+---------+--------- | | | | | | Number and| | | | | | kind of | | | | | | wings | | | | | | | | | | | | ----------+---------+---------+---------+---------+---------+--------- | | | | | | Descrip- | | | | | | tion of | | | | | | legs | | | | | | | | | | | | ----------+---------+---------+---------+---------+---------+--------- | | | | | | Antennæ | | | | | | (length, | | | | | | shape, | | | | | | joints) | | | | | | | | | | | | ----------+---------+---------+---------+---------+---------+--------- | | | | | | Biting or | | | | | | sucking | | | | | | mouth | | | | | | parts | | | | | | | | | | | | ----------+---------+---------+---------+---------+---------+--------- | | | | | | Complete | | | | | | or | | | | | | incomplete| | | | | | metamor- | | | | | | phosis | | | | | | | | | | | | ==========+=========+=========+=========+=========+=========+=========

[Illustration: FIG. 141.--CODLING MOTH, from egg to adult. (See Farmers’ Bulletin, p. 95.)]

[Illustration: FIG. 142.--CABBAGE BUTTERFLY, male and female, larva and pupa.]

[Illustration: FIG. 143.--LIFE HISTORY OF SILKWORM.]

[Illustration: FIG. 144.--SCALES FROM BUTTERFLIES’ WINGS, as seen under microscope.]

TO THE TEACHER: _These illustrated studies require slower and more careful study than the text. One, or at most two, studies will suffice for a lesson. The questions can be answered by studying the figures. Weak observers will often fail and they should not be told, but should try again until they succeed._

[Illustration: FIG. 145.--SCALES ON MOTH’S WING.]

[Illustration: FIG. 146.--HEAD OF BUTTERFLY.]

[Illustration: FIG. 147.--SECTION OF PROBOSCIS of butterfly showing lapping joint and dovetail joint.]

[Illustration: FIG. 148.--HEAD OF BUTTERFLY (side view).]

FIGS. 141-148. =Illustrated Study of Lepidoptera.=--Study the stages in the development of _codling moth_, _silkworm moth_, and _cabbage butterfly_.

Where does each lay its eggs? What does the larva of each feed upon? Describe the pupa of each. Describe the adult forms. Find the _spiracles_ and _prolegs_ on the silkworm. Compare _antennæ_ of moth and butterfly. Which has larger body compared to size of wings?

Describe the _scales_ from a butterfly’s wings as seen under microscope (144). How are the scales arranged on moth’s wing (145)? By what part is scale attached to wing? Do the scales overlap?

Study butterfly’s head and _proboscis_ (Figs. 146-148). What shape is compound eye? Are the antennæ jointed? Is the proboscis jointed? Why not call it a tongue? (See text.)

Which mouth parts have almost disappeared? What is the shape of cut ends of halves of proboscis? How are the halves joined to form a tube?

If you saw a butterfly on a flower, for what purpose would you think it was there? What, if you saw it on a leaf? How many spots on fore wing of female cabbage butterfly? (Fig. 124, above.)

Does the silkworm chrysalis fill its cocoon? Eggs may be obtained from U. S. Dept. of Agriculture.

[Illustration: FIG. 149.]

[Illustration: FIG. 150.]

[Illustration: FIG. 151.]

[Illustration: FIG. 152.]

[Illustration: FIG. 153.]

[Illustration: FIG. 154.]

[Illustration: FIG. 155.]

[Illustration: FIG. 156.]

[Illustration: FIG. 157.]

[Illustration: FIG. 158.--Anatomy of bee.]

FIGS. 149-161. =Illustrated Study of Bees and their Kindred.=--Head of worker (Fig. 149): _o_, upper lip; _ok_, chewing jaws; _uk_, grasping jaws; _kt_, jaw finger; _lt_, lip finger; _z_, tongue.

How do heads of drone (150) and queen (151) differ as to mouth, size of the two compound eyes, size and position of the three simple eyes? Is the head of a worker more like head of drone or head of queen? Judging by the head, which is the queen, drone, and worker in Figs. 154-156? Which of the three is largest? Smallest? Broadest?

Figure 152 shows hind leg of worker. What surrounds the hollow, _us_, which serves as pollen basket? The point, _fh_, is a tool for removing wax which is secreted (_c_, Fig. 157) between rings on abdomen. In Fig. 158, find relative positions of heart, _v_, food tube, and nerve chain. Is crop, _J_, in thorax or abdomen? In this nectar is changed to honey, that it may not spoil. Compare nerve chain in Fig. 132.

[Illustration: FIG. 159.--Ichneumon fly.]

[Illustration: FIG. 160.]

[Illustration: FIG. 161.--Wasp using pebble.

From Peckham’s “Solitary Wasps,” Houghton, Mifflin & Co.]

Compare the cells of _bumble bee_ (Fig. 153) with those of hive bee. They differ not only in shape but in material, being made of web instead of wax, and they usually contain larvæ instead of honey. Only a few of the queens among bumble bees and wasps survive the winter. How do ants and honey bees provide for the workers also to survive the winter? Name all the social insects that you can think of. Do they all belong to the same order?

The ichneumon fly shown enlarged in Fig. 159 lays its eggs under a caterpillar’s skin. What becomes of the eggs? The true size of the insect is shown by the cross lines at _a_. The eggs are almost microscopic in size. The pupæ shown (true size) on caterpillar are sometimes mistaken for eggs. The same mistake is made about the pupa cases of ants. Ichneumon flies also use tree-borers as “hosts” for their eggs and larva. Is this insect a friend of man?

The _digging wasp_ (Figs. 160 and 161) supplies its larva with caterpillars and closes the hole, sometimes using a stone as pounding tool. Among the few other uses of tools among lower animals are the elephant’s use of a branch for a fly brush, and the ape’s use of a walking stick. This wasp digs with fore feet like a dog and kicks the dirt out of the way with its hind feet.

Are the wings of bees and wasps more closely or less closely veined than the wings of dragon flies? (Fig. 177.) For an interesting account of the order “Joined-wings” (bees and their kindred) see Comstock’s “Ways of the Six-footed,” Ginn & Co.

=Illustrated Study of Beetles.=

[Illustration: FIG. 162.--Diving beetle (_Dysticus_), with larva, _a_.]

[Illustration: FIG. 163.--Weevil.]

[Illustration: FIG. 164.]

[Illustration: FIG. 165.]

[Illustration: FIG. 166.--Click beetle.]

[Illustration: FIG. 167.--MAY BEETLE.]

[Illustration: FIG. 168.]

[Illustration: FIG. 169.--Colorado beetle (potato bug).]

=Illustrated Study of Beetles= (Figs. 162-169).--Write the life history of the _Colorado beetle_, or potato bug (Fig. 169), stating where the eggs are laid and describing the form and activities of each stage (the pupal stage, _b_, is passed in the ground).

Do the same for the MAY BEETLE (Figs. 167-168). (It is a larva--the white grub--for three years; hogs root them up.) Beetles, like moths, may be trapped with a lantern set above a tub of water.

Where does a _Scarab_ or sacred beetle of the Egyptians, also called tumble bug (Fig. 164), lay its eggs (Fig. 165)? Why?

How does the _click beetle_, or jack snapper (Fig. 166), throw itself into the air? For what purpose?

The large proboscis of the _weevil_ (Fig. 163) is used for piercing a hole in which an egg is laid in grain of corn, boll of cotton, acorn, chestnut, plum, etc.

How are the legs and body of the _diving beetle_ suited for swimming (Fig. 162)? Describe its larva.

What is the shape of the lady bug (Fig. 97)? It feeds upon plant lice (Fig. 185). Is any beetle of benefit to man?

[Illustration: FIG. 170.--Life history of ant lion.]

=Illustrated Study of Ant Lion, or Doodle Bug= (Fig. 170).--Find the pitfall (what shape?); the larva (describe it); the pupa case (ball covered with web and sand); the imago. Compare imago with dragon fly (Fig. 177).

How does ant lion prevent ant from climbing out of pitfall (see Fig. 170)? What is on edge of nearest pitfall? Explain.

Ant lions may be kept in a box half filled with sand and fed on ants. How is the pitfall dug? What part of ant is eaten? How is unused food removed?

How long is it in the larval state? Pupal state? Keep net over box to prevent adult from flying away when it emerges.

[Illustration: FIG. 171.]

[Illustration: FIG. 172.--Metamorphosis of house fly (enlarged).]

[Illustration: FIG. 173.--Metamorphosis of flea.]

[Illustration: FIG. 174.--Louse.]

[Illustration: FIG. 175.--Bed bug. × 5.]

[Illustration: FIG. 176.--Life history of mosquito.]

=Illustrated Study of Insect Pests= (Figs. 171-176).--Why does the _clothes moth_ (171) lay its eggs upon woolen clothing? How does the larva conceal itself? The larva can cut through paper and cotton, yet sealing clothes in bags of paper or cotton protects them. Explain.

The _house fly_ eats liquid sweets. It lays its eggs in horse dung. Describe its larval and pupal forms. Banishing horses from city would have what beneficial effect?

Describe the _louse_ and its eggs, which are shown attached to a hair, natural size and enlarged.

Describe the _bed bug_. Benzine poured in cracks kills bed bugs. Do bed bugs bite or suck? Why are they wingless?

Describe the larva, _f_, pupa, _g_, and the adult _flea_, all shown enlarged. Its mandibles, _b_, _b_, are used for piercing. To kill fleas lather dog or cat completely and let lather remain on five minutes before washing. Eggs are laid and first stages passed in the ground.

How does the _mosquito_ lay its eggs in the water without drowning (176)? Why are the eggs always laid in still water? Which part of the larva (wiggletail) is held to the surface in breathing? What part of the pupa (called tumbler, or bull head) is held to the surface in breathing? Give differences in larva and pupa. Where does pupa change to perfect insect? Describe mouth parts of male mosquito (at left) and female (at right). Only female mosquitoes suck blood. Males suck juice of plants. Malarial mosquito alights with hind end of body raised at an angle. For figure see Human Biology, Chap. X. Why does killing fish and frogs increase mosquitoes? 1 oz. of kerosene for 15 ft. of surface of water, renewed monthly, prevents mosquitoes.

What is the use to the squash bug (Fig. 184) of having so bad an odor?

[Illustration: FIG. 177.]

FIG. 177. =Illustrated Study of Dragon Fly.=--3 shows dragon fly laying its eggs in water while poised on wing. Describe the larval form (water tiger). The extensible tongs are the maxillæ enlarged. The pupa (1) is active and lives in water. Where does transformation to adult take place (5)? Why are eyes of adult large? its legs small? Compare front and hind wings.

Do the eyes touch each other? Why is a long abdomen useful in flight? Why would long feelers be useless? What is the time of greatest danger in the development of the dragon fly? What other appropriate name has this insect? Why should we never kill a dragon fly?

[Illustration: FIG. 178.--The tarantula.]

[Illustration: FIG. 179.--Trap-door spider.]

[Illustration: FIG. 180.]

[Illustration: FIG. 181.--Anatomy of spider.]

[Illustration: FIG. 182.--Laying egg.]

[Illustration: FIG. 183.--Foot of spider.]

=Illustrated Study of Spiders= (Figs. 178-183).--The tarantula, like most spiders, has eight simple eyes (none compound). Find them (Fig. 178). How do spiders and insects differ in body? Number of legs? Which have more joints to legs? Does trap-door spider hold the door closed (Fig. 179)? How many pairs of spinnerets for spinning web has a spider (_Spw_, 180)? Foot of spider has how many claws? How many combs on claws for holding web? Spiders spin a cocoon for holding eggs. From what part of abdomen are eggs laid (_E_, 182; 2, 181)? Find spider’s air sacs, _lu_, Fig. 181; spinning organs, _sp_; fang, _kf_; poison gland, _g_; palpi, _kt_; eyes, _au_; nerve ganglia, _og_, _ug_; sucking tube, _sr_; stomach, _d_; intestine, _ma_; liver, _le_; heart, _h_, (black); vent, _a_. Give two reasons why a spider is not an insect. How does it place its feet at each step (Fig. 110)? Does the size of its nerve ganglia indicate great or little intelligence? Why do you think first part of body corresponds to both head and thorax of insects?

[Illustration: FIG. 184.--Squash bug, or stink bug.]

The following Farmer’s Bulletins are available for free distribution to those interested, by the U. S. Department of Agriculture, Washington, D.C.:--

Farmer’s Bulletin No. 47, Insects affecting the Cotton Plant; No. 59, Bee Keeping; No. 70, The Principal Insect Enemies of the Grape; No. 80, The Peach Twig Borer; No. 99, Three Insect Enemies of Shade Trees; No. 120, The Principal Insects affecting the Tobacco Plant; No. 127, Important Insecticides; No. 132, The Principal Insect Enemies of Growing Wheat; No. 145, Carbon Bisulphid as an Insecticide; No. 146, Insecticides and Fungicides; No. 152, revised, Mange in Cattle; No. 153, Orchard Enemies in the Pacific Northwest; No. 155, How Insects affect Health in Rural Districts; No. 159, Scab in Sheep; No. 165, Silkworm Culture; No. 171, The Control of the Codling Moth; No. 172, Scale Insects and Mites on Citrus Trees; No. 196, Usefulness of the Toad; No. 209, Controlling the Boll Weevil in Cotton Seed and at Ginneries; No. 211, The Use of Paris Green in controlling the Cotton Boll Weevil; No. 212, The Cotton Bollworm; No. 216, The Control of the Boll Weevil; No. 223, Miscellaneous Cotton Insects in Texas; No. 247, The Control of the Codling Moth and Apple Scab.

[Illustration: FIG. 185.--Female plant louse, with and without wings (enlarged).]

The following bulletins of the Bureau of Entomology may be obtained from the same source at the prices affixed: Bulletin No. 25 (old series), Destructive Locusts, 15c.; No. 1 (new series), The Honey Bee, 15c.; No. 3, The San José Scale, 10c.; No. 4, The Principal Household Insects of the U. S., 10c.; No. 11, The Gypsy Moth in America, 5c.; No. 14, The Periodical Cicada, 15c.; No. 15, The Chinch Bug, 10c.; No. 16, The Hessian Fly, 10c.; Nos. 19, 23, and 33, Insects Injurious to Vegetables, 10c. each; No. 25, Notes on Mosquitoes of the U. S., 10c.; No. 42, Some Insects attacking the Stems of Growing Wheat, Rye, Barley, and Oats, 5c.; No. 50, The Cotton Bollworm, 25c.; No. 51, The Mexican Boll Weevil, 25c.

Bureau of Plant Industry--Bulletin No. 88, Weevil-resisting Adaptations of the Cotton Plant, 10c. This gives an instructive account of the struggle of a plant for existence against an insect enemy.

[Illustration: FIG. 186.--Gall fly (enlarged) and oak gall with larva, and one from which a developed insect has escaped.]

[Illustration: FIG. 187.--PLAN OF MOUTH PARTS OF THE INSECT ORDERS. _A_, straight wings, nerve wings, false nerve wings; _B_, joined wings; _C_, scaly wings; _D_, half wings; _E_, two wings.

_ol_, upper lip; _ok_, biting jaws; _uk_, holding jaws; _ul_, under lip; _kt_, jaw fingers; _lt_, lip fingers.]

[Illustration]

[Illustration: Pearl divers.]