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 moults,
place sod in the bottom of a box and cover the box with mosquito
netting or wire gauze.
[Illustration:
FIG. 106.—A GRASSHOPPER.
]
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 crayfish? What
is the length of your specimen? Its colour? Why does it have this
coloration? In what ways does the grasshopper resemble the crayfish?
Differ from it?
=The Three Regions of the Body.=—The body of the grasshopper is divided
into three regions—the _head_, the _thorax_, and the _abdomen_. Which of
these three divisions has no distinct subdivisions? The body of the
grasshopper, like that of the earth worm, is made of _ringlike
segments_. Are the segments most distinct in the head, the thorax, or
the 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 in 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?
[Illustration:
FIG. 107.—A GRASSHOPPER DISSECTED.
]
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?
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.
[Illustration:
FIG. 108.—GRASSHOPPER LAYING EGGS. (Riley.)
]
=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 two appendages 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, the grasshopper makes a
pit almost as deep as the abdomen is long. The eggs are laid in the
bottom of the pit.
=Draw= a side view of the grasshopper.
=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 of the thorax is called _prothorax_. 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 the 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 purpose different from that of the
other legs?
[Illustration:
FIG. 109.—HOW A GRASSHOPPER WALKS.
]
[Illustration:
FIG. 110.—HOW A SPIDER WALKS.
]
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 the 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?
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?
[Illustration:
FIG. 112.—GRASSHOPPER IN FLIGHT.
]
Compare the first and second pairs of wings in shape, size, colour,
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?
=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 the neck? Is the head
movable in all directions?
What is the position of the large =eyes=? Like the eyes of the crayfish,
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 crayfish?
[Illustration:
FIG. 113.
]
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 also are organs of
hearing and smelling.
The =mouth parts= of a grasshopper should be compared with the mouth
parts of a beetle shown in Fig. 113, since they correspond closely. If
the grasshopper is fed with a blade of fresh grass, the function of each
organ 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.
[Illustration:
FIG. 115.—EGG AND MOULTS OF A GRASSHOPPER.
]
=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.
=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 retards further growth until the insect moults, the skin
first splitting above the prothorax. After hatching, there are five
successive periods of growth. At which moult do the very short wings
first appear? (Fig. 115.) After the last moult 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 family, and to call the shorter winged, stouter
family 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.
]
[Illustration:
FIG. 120.—FRONT LEG OF MOLE CRICKET. × 3.
]
=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 grasshopper ravages in 1874–5.
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 noxious insects. Which of its
legs are specialized? The _walking stick_ (Fig. 121) and the _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 colours have you seen on grasshoppers? Which colours
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.
=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 crayfish, tadpoles, and the eggs of frogs and toads should also
be collected, if found.) Moths may be caught at night by daubing
molasses or syrup 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.
Captured insects which, in either the larval or the 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 is divided by means of two marked narrowings
into three parts: the head, the chest, and the abdomen.
[Illustration:
FIG. 122.—YELLOW FEVER MOSQUITO, showing head, thorax, abdomen.
]
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 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
adult animals have that number, the spider having eight, the crayfish
and crabs having ten, the centipedes still more, while 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.
[Illustration:
FIG. 126.—FOOT OF FLY, with climbing pads.
]
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. 161) is thickest? Slenderest? Shortest? One
joint (which?) of the foot (Fig. 161) 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.
The =abdomen= in various species consists of from five to eleven
overlapping rings with their fold-like joints between them. Does each
ring overlap the ring in front or the one behind it?
[Illustration:
FIG. 127.—VISCERA OF GRASSHOPPER. Key in text. Compare with Fig. 114.
]
[Illustration:
FIG. 128.—AIR TUBES OF INSECT.
]
The =food tube= (Fig. 127) begins at the mouth, which usually bears
salivary glands (4, Fig. 127, which represents internal organs of the
grasshopper). The food tube expands first into a _croplike_ enlargement;
next to this is an organ (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 the large intestine (9) are
a number of _fine tubes_ (8) which correspond to _kidneys_ and empty
their secretion into the large intestine.
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 dioxide, 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 colour. The blood is sent even to the
wings. The veins in the wings consist of horny tubes inclosing air tubes
surrounded by blood spaces, and the purification of the blood takes
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 unequalled by
any other animals.
[Illustration:
FIG. 132.—NERVOUS SYSTEM OF BEE.
]
[Illustration:
FIG. 133.—FEELER of a beetle.
]
=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 the 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.
=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 centre 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 the moulting 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.
]
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 the imago, and no
pupal stage, the metamorphosis, or change, is said to be _complete_.
When, as with the grasshopper, no very marked change takes place between
the larva and the imago, there being no pupal stage, 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.
[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.
]
RECOGNITION-CHARACTERS FOR THE PRINCIPAL ORDERS OF ADULT WINGED INSECTS
(All are wingless when young, and wingless adult forms occur in all the
orders: order APTERA lacks wing-bearing thoracic structures.)
A single pair of wings is characteristic of the order DIPTERA.
A jointed beak, that is sheath-like, inclosing the other mouth parts, is
characteristic of the order HEMIPTERA.
A coiled sucking proboscis and a wing covering of dust-like microscopic
scales are characteristic of the order LEPIDOPTERA.
Horny sheath-like fore wings, covering the hind wings and meeting in a
straight line down the middle of the back, will distinguish the order
COLEOPTERA.
Hind wings folded like a fan beneath the thickened and overlapping fore
wings, will distinguish most members of the order ORTHOPTERA.
The possession of a sting (in females) and of two pairs of thin
membranous wings—the small hind wing hooked to the rear margin of the
fore wing—will distinguish the common HYMENOPTERA.
Besides these, there remain a number of groups most of which have in the
past been included under the order NEUROPTERA, among which the Mayflies
will be readily recognized by the lack of mouth parts and by the
possession of two or three long tails; the dragon flies by the two pairs
of large wings, enormous eyes, and minute bristle-like antennæ; the
scorpion flies, by the possession of a rigid beak, with the mouth parts
at its tip; the caddis flies, by their hairy wings and lack of jaws; the
lace wings, by the exquisite regularity of the series of cross veins
about the margin of their wings, etc.
[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
a 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 in the wind.
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 the 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 prolegs, one pair of which is always on the
last segment. How many pairs of prolegs 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 moult. Hairy caterpillars are
uncomfortable for birds to eat. The naked and brightly marked ones
(examples of 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 estimated 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 a zigzag course? Advantage of this? Bright colours are
protective, as lepidoptera are in greatest danger when at rest on
flowers. Are the brightest colours on upper or under side of wings of
butterfly? Why? (Think of the colours 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 colour of the wings is given by
the scales?
State =how moths and butterflies differ= in respect to: body, wings,
feelers, habits.
=Insects and Flowers.=—Perhaps we are indebted to insects for the bright
colours 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
colours and sweet odours are the advertisements of the flowers to
attract insects. Flowers of brightest hues are the ones that receive the
visits of insects. Moths, butterflies, and bees carry most pollen (see
Beginners’ Botany, Chap. VI).
=Comparative Study.=—Make a table like this, occupying entire page of
notebook, leaving no margins, and fill in accurately:—
═════════════════╤═══════════╤═════════╤═══════╤═══════╤═══════╤═══════
│GRASSHOPPER│BUTTERFLY│FLY pp.│DRAGON │BEETLE │BEE pp.
│ │ │92, 93 │FLY p. │pp. 90,│88, 89
│ │ │ │ 93 │ 91 │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Number and kind │ │ │ │ │ │
of wings │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Description of │ │ │ │ │ │
legs │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Antennæ (length, │ │ │ │ │ │
shape, joints) │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Biting or sucking│ │ │ │ │ │
mouth parts │ │ │ │ │ │
─────────────────┼───────────┼─────────┼───────┼───────┼───────┼───────
Complete or │ │ │ │ │ │
incomplete │ │ │ │ │ │
metamorphosis. │ │ │ │ │ │
═════════════════╧═══════════╧═════════╧═══════╧═══════╧═══════╧═══════
[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.
]
[Illustration:
FIG. 145.—SCALES ON MOTH’S WING.
]
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._
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?
[Illustration:
FIG. 146.—HEAD OF BUTTERFLY.
]
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?
[Illustration:
FIG. 148.—HEAD OF BUTTERFLY (side view).
]
[Illustration:
FIG. 147.—SECTION OF PROBOSCIS of butterfly showing lapping joint and
dovetail joint.
]
[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.
]
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?
[Illustration:
FIG. 160.
]
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?
[Illustration:
FIG. 161.—Wasp using pebble.
From Peckham’s “Solitary Wasps,” Houghton, Mifflin & Co.
]
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.)
=Illustrated Study of Beetles.=
[Illustration:
FIG. 162.—Diving beetle (_Dytiscus_), 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 and its eggs attached to a hair. Natural size and
magnified.
]
[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 woollen 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. 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
odour?
[Illustration:
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?
The following Farmer’s Bulletins, (revised to 1921) are available for
distribution to those interested, by the United States Department of
Agriculture, Washington, D.C.—
Farmer’s Bulletin No. 47, Insects Affecting the Cotton Plant; No. 447,
Bee Keeping; No. 440, The Peach Twig Borer; No. 120, The Principal
Insects Affecting the Tobacco Plant; No. 856, Important Insecticides;
No. 835, The Principal Insect Enemies of Growing Wheat; No. 799, Carbon
Bisulphide as an Insecticide; No. 243, Insecticides and Fungicides; No.
152 (revised) Mange in Cattle; No. 155, How Insects Affect Health in
Rural Districts; No. 492, 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. 872, The Cotton Bollworm; No. 848, The Control of the
Boll Weevil; No. 223, Miscellaneous Cotton Insects in Texas; No. 908,
The Control of the Codling Moth and Apple Scab.
Bulletins of the Bureau of Entomology may be obtained from the same
source, while the supply lasts, as follows:
Destructive Locusts; The Honey Bee; The San José Scale; The Principal
Household Insects of the United States; The Gypsy Moth in America; The
Periodical Cicada; The Chinch Bug; The Hessian Fly; Insects Injurious to
Vegetables; Notes on Mosquitoes; Some Insects Attacking the Stems of
Growing Wheat, Rye, Barley, and Oats.
Bulletins on Similar Topics, Published by the Department of Agriculture,
Ontario—
(Write to the Publications Branch)
Bulletin No. 187—The Codling Moth
Bulletin No. 195—The Insecticides and Fungicides
Bulletin No. 198—Lime Sulphur Wash
Bulletin No. 219—The San José and Oyster-shell Scales
Bulletin No. 241—Peach Growing in Ontario
Bulletin No. 250—Insects Attacking Fruit Trees
Bulletin No. 251—Insects Affecting Vegetables
Bulletin No. 256—The Wintering of Bees
Bulletin No. 257—The More Important Fruit Tree Diseases in Ontario
Bulletin No. 258—The More Important Fungus and Bacterial Diseases of
Vegetables in Ontario
Bulletin No. 271—The Apple Maggot
Bulletin No. 276—Bee Diseases in Ontario
Bulletins Published by the Department of Agriculture, Ottawa—
(Write to the Publications Branch)
Bulletin No. 9—The Army Worm
Bulletin No. 10—Cutworms and their Control
Bulletin No. 26—Bees and How to Keep Them
Circular No. 9—1921—Common Garden Insects and their Control
[Illustration:
Pearl divers.
]