[Illustration:
FIG. 57.—A Grasshopper, with the different regions of the body
separated from one another. A, head; B, thorax: _I._, prothorax;
_II._, mesothorax; _III._, metathorax; C, abdomen; _a_, antennæ;
_b_, eyes; _c_, _d_, _e_, legs; _f_, _g_, wings; _p_, shank; _q_,
foot.
]
Breathe by tracheæ (cp. p. 84). The segments fuse into three body
regions (Fig. 57). These are—(1) the _Head_, bearing the eyes, feelers
(antennæ), and jaws; (2) the _Thorax_, composed of three fused segments,
of which the first (prothorax) bears a pair of legs, while the second
(mesothorax) and third (metathorax) not only bear a pair of legs each,
but also sometimes a pair of wings in addition; (3) the _Abdomen_, which
possesses no limbs, and of which the number of segments is not always
the same. These three regions of the body perform different functions;
the head is concerned with sensation and the taking up of food, the
thorax with movement, while the abdomen contains the organs of digestion
and reproduction. I will now deal somewhat more fully with the different
body regions of an insect.
_Head._—Almost all insects have in the adult state a compound eye,
_i.e._ an eye made up of a large number (up to ten thousand) of smaller
eyes. In many insects one finds in addition to this a few simple eyes on
the top of the head. The feelers are very unlike in different insects;
they serve as organs of touch, and perhaps also help some other sense.
The mouth-parts consist of three pairs of jaws, of which the first (the
mandibles) and the second pair (maxillæ) are freely movable from side to
side, while the third consists of two jaws immovably fused together
(lower lip, or labium). A downward projection of the skin of the head
(the upper lip, or labrum) overhangs the three pairs of jaws (Fig. 58).
In insects which feed on solid matters, tearing or chewing them, the
jaws are short and sharp-edged (biting mouth-parts); in those which take
up fluid food (blood, the juices of plants, etc.) they are elongated,
and adapted for licking, sucking, or piercing.
[Illustration:
FIG. 58.—Head and Mouth-parts of a Ground Beetle, enlarged four times.
A, from above; B, from below. _a_, labrum; _b_, mandible; _f_,
maxilla with palpi (_g_); _c_, labium with palp (_e_).
]
_Thorax._—The names of the parts of the legs are for the most part those
used in the case of mammalian limbs; though the similarity between the
limbs of Mammals and Insects is quite superficial. The following parts
are distinguished in the leg of an insect: (1) the generally spherical
hip (_coxa_) (Fig. 59, _a_); (2) the very short _trochanter_ (_b_); (3)
the elongated thigh (_femur_) (_c_); (4) the shank (_tibia_) provided
with movable spines at its tip (_d_); (5) the three- to five-jointed
foot (_tarsus_) (_e_), whose last joint ends in claws, and often also in
flap-like outgrowths. The _Wings_ are expansions of the skin, which
consist of two layers. There are tracheæ between the upper and lower
lamellæ. At first (in the pupa) the wings are folded up; but the forcing
of air into the tracheæ quickly causes them to unfold. A firm substance
is now deposited in the larger tracheæ, which are thus converted into
veins or ribs giving support to the wings. In beetles the fore wings are
quite hard and horny, and serve for protecting the delicate hind wings
and soft back rather than for flight; they are therefore named
“wing-covers” (_elytra_). In many insects the fore wings (wasps) or the
hind wings (beetles, grasshoppers) are folded when at rest.
[Illustration:
FIG. 59.—Leg of a Ground Beetle (× 2).
]
[Illustration:
FIG. 60.—Silkworm Moth (_Bombyx mori_). Female moth, caterpillar, pupa
and cocoon.
]
The _abdomen_ only bears organs of movement in caterpillars (Fig. 60)
and a few other insects in the young condition, and in these cases they
are not jointed like the true legs or “thoracic feet,” but unjointed
pro-legs or “abdominal feet.” In the adult insect the abdomen may have
thread-like (mole-cricket) or pincer-like (earwig) appendages; or
appendages used in egg-laying (ovipositors, _e.g._ Locust).
Most insects have great powers of reproduction. A few bring forth living
young, but most insects lay eggs. It is only in a few (_e.g._ lice) that
animals exactly like their parents are hatched from the eggs; the large
majority of insects pass through a _change_, or _metamorphosis_.
A distinction is drawn between _complete_ and _incomplete_
metamorphosis. It is said to be complete when the insect passes through
a stage in which it takes up no food, and, as a rule, moves but little.
In this condition of almost complete rest the insect is called a “pupa”
(Figs. 60, 61, 65). The metamorphosis is called incomplete when the
insect does not pass through a pupa stage, and therefore feeds and moves
during all the periods of its development, merely altering its form
somewhat during its various moults (Fig. 62).
[Illustration:
FIG. 61.—The Hornet (_Vespa crabro_), with larva and pupa.
]
The word “moult” must here be explained. The covering of the skin of
Arthropods consists of hard parts incapable of being stretched. At the
end of a definite period of time this firm covering is stripped off and
replaced by a new investment, soft at first, but afterwards becoming
hard. In this way growth can be effected in spite of the hard
integument. Everyone must have noticed at some time or other the
moulting of caterpillars.
[Illustration:
FIG. 62.—The Migratory Grasshopper (_Acrydium migratorium_). Larva and
adult female.
]
[Illustration:
FIG. 63.—Looper Caterpillar.
]
[Illustration:
FIG. 64.—False Caterpillar.
]
In insects with incomplete metamorphosis the form of the animal alters a
little at every moult, becoming more and more like that of the adult
insect. In the last moult but one small imperfect wings appear (Fig. 62,
_left_), and fully developed wings are only present after the last
moult. The ovipositors of female insects, in those cases where the
metamorphosis is incomplete, first appear as fully developed organs in
the perfect condition of the animal, but begin to develop in the
preceding stage. In cases of this kind of metamorphosis the young insect
(“larva”) closely resembles the adult in form even in the first stage of
development. In insects undergoing complete metamorphosis the difference
between larva and adult insect (imago) is much greater (Figs. 60, 61,
65).
[Illustration:
FIG. 65.—The Common Cockchafer (_Melolontha vulgaris_). Larva, pupa,
female flying, and male creeping out of the earth.
]
The time passed in the pupa state by insects with complete metamorphosis
is by no means always of the same length. For example, there are two
generations annually of the cabbage white butterfly; one lives through
the winter in the pupa state, the pupæ of the other are found in summer.
So that while an insect of the winter generation lives about half a year
in the pupa state, this condition lasts only about a month in the summer
generation. A higher temperature hastens the development.
Although the insect in the pupa state takes no food, it nevertheless
breathes, and therefore continually uses up body substance. This using
up only takes place to a small extent however, since the animal moves
but little. From whence, then, does the pupa get the material to cover
the loss of body substance? In the larval condition the insect takes far
more food than it requires for the development of its body, and from
this excess it builds up reserve stuffs, which are deposited in the
so-called “fat-bodies” of the larva. These reserve materials are
re-absorbed during the pupa state, and serve to maintain the breathing.
Consequently a pupa that has just been formed moves more than another
one just about to become a butterfly.
[Illustration:
FIG. 66.—Larva of a Weevil.
]
[Illustration:
FIG. 67.—A Hover Fly (_Syrphus pyrasti_). Fly, maggot, and pupa case.
]
The larvæ and pupæ of the different kinds of insects which undergo a
complete metamorphosis have not the same shape of body. Among the larvæ
may be distinguished _caterpillars_, _grubs_, and _maggots_. The
_caterpillars_ (Fig. 60) have a clearly marked head with hard covering,
three pairs of jointed thoracic legs, and a varying number of unjointed
pro-legs. They are usually variegated or green in colour, and are
divided into _true caterpillars_ and _false caterpillars_ (Figs. 60, 63,
and 64). The first, after the resting pupa stage, become butterflies or
moths; the latter saw-flies. The true caterpillars have two to five
pairs of pro-legs, the false caterpillars six to eight pairs. Reckoning
in the thoracic legs, therefore, the true caterpillars have altogether
five to eight, the false caterpillars nine to eleven pairs. The head of
the latter is more rounded, while that of the former is more flattened.
The way in which caterpillars walk depends upon the number of their
legs. If this is fairly large so that most of the segments of the body
are provided with legs, the whole body remains tolerably extended during
progression. But if the number is small—as in the looper caterpillars,
where there are three pairs of thoracic legs at the anterior end, and at
the posterior end only a terminal pair of legs (the caudal pro-legs) and
another pair in front of them—the middle legless region is strongly bent
during locomotion (Fig. 63). Hence the name “looper.” The loopers often
bend their bodies in a characteristic way. When at rest the hinder part
is coiled up spirally; but as soon as the animals are alarmed they throw
the hinder part of the body upwards and forwards and even over the head.
The _grubs_ (Figs. 66 and 69, _left_) have indeed, like the
caterpillars, a clearly visible hard head, but no characteristic
abdominal legs, or at most a pair of sucker feet at the end of the body
(wireworms). Thoracic legs are present in several grubs (cockchafer
larvæ, wireworms, leaf beetles); in others (larvæ of weevils and fleas)
they are entirely absent. _Maggots_ are those entirely footless insect
larvæ which do not possess a head clearly marked off from the rest of
the body, and the head-end of which is only to be recognized by the
presence of the mouth and mouth-parts. _Pupæ_ are enclosed in a case
which either only faintly indicates the outline of the various parts of
the adult insect, or else closely surrounds every part of the
body—wings, legs, antennæ, and even the mouth-parts and eyes. Pupæ of
the first kind are termed _obtectate_ (Fig. 60); those of the second,
_free_ (Figs. 61, 65).
Many pupæ are _naked_, others are surrounded by a web (cocoon) spun by
the larva (Fig. 60). There are also pupæ distinguished by the
peculiarity that when the insect has lived through the maggot-stage it
does not strip off its integument, but turns into a pupa inside the
shrivelled maggot-skin, from which the perfect insect later on breaks
out (Fig. 67).
The class of insects can be divided into eleven orders: (1) _Coleoptera_
(Beetles); (2) _Orthoptera_ (Grasshoppers, Locusts); (3) _Neuroptera_
(Dragon-flies); (4) _Hymenoptera_ (Bees, Ants, Saw-flies); (5)
_Lepidoptera_ (Butterflies and Moths); (6) _Hemiptera_ (Aphides, Bugs);
(7) _Physopoda_ (Thrips); (8) _Diptera_ (Flies with two wings); (9)
_Aphaniptera_ (Fleas); (10) _Pediculina_ (Lice); (11) _Collembola_
(Spring-tails and Tassel-tails).
ORDER I.: =Coleoptera= (BEETLES).
Beetles (Fig. 65) are insects with biting mouth-parts, and strongly
developed prothorax united with the mesothorax so as to permit free
movement. The fore wings are in the form of hard covers, leaving exposed
only the head, neck-shield (_i.e._ the dorsal side of the prothorax), a
three-cornered bit of the mesothorax (_scutellum_), and sometimes the
tip of the abdomen. Flight is effected by the hind wings alone, which in
a state of rest are drawn back under the wing-covers. The metamorphosis
is complete; the larvæ are legless, or with thoracic legs only, and have
a hard head with biting mouth-parts; change into free pupæ (p. 93).
Family: =Carabidæ= (_Ground Beetles_).
Usually elongated, slender; with long slender legs, five-jointed tarsi,
eleven-jointed antennæ, powerful jaws (Figs. 68, 69). Run rapidly;
usually keep on the ground; hide themselves during the day, but are very
active at night; with very few exceptions feed entirely on other
insects; when touched squirt an acrid stinking fluid out of the abdomen.
Larvæ longish, six-legged, with short antennæ and sharp jaws, with a few
exceptions live exclusively on other insects and lower animals.
Several species are of service, both in the adult and larval conditions,
since they destroy injurious insects, _e.g._ surface caterpillars,
wireworms, cockchafers, grubs, crane-fly larvæ. The following do good in
cultivated fields: =Golden Ground Beetle= (_Carabus auratus_), =Garden
Ground Beetle= (_C. hortensis_), =Granulated Ground Beetle= (_C.
granulatus_), =Cross-barred Ground Beetle= (_C. cancellatus_), =Field
Ground Beetle= (_C. nemoralis_), =Large-headed Ground Beetle=
(_Cephalotes vulgaris_), species of _Harpalus_, _Pterostichus_, etc.
[Illustration:
FIG. 68.—A Ground Beetle (_Carabus auronitens_).
]
[Illustration:
FIG. 69.—Corn Ground Beetle (_Zabrus gibbus_) and larva.
]
The only destructive form is the =Corn Ground Beetle= (_Zabrus gibbus_,
Fig. 69); short, thick-set; back black; belly, legs, and antennæ dark
brown. Larva cylindrical, slightly hairy, brown, with yellowish white
belly; head broad and flattened, black. The beetles (June, July) usually
remain hidden in the soil during the day, climbing up the stalks of
barley, wheat, and rye during the evening and in dull weather, and
eating the grain in the ear. The larvæ remain during the day in vertical
holes which they dig out; but at night and during dull weather they
devour the overground parts of the grain-plants mentioned above,
especially the hearts of young plants. They are destructive both in
autumn and spring, damaging winter and summer grain. The larval
condition is maintained for three years, the animal then turning into a
pupa during July. Its ravages are limited to special years. _Remedy_:
Sowing oats, peas, or vetches, or planting potatoes in fields infested
by the beetles or their larvæ; collecting the beetles in the evening
when they are in the ears.
Family: =Staphylinidæ= (_Rove Beetles_).
[Illustration:
FIG. 70.—Rove Beetle (_Staphylinus erythropterus_).
]
[Illustration:
FIG. 71.—The Black Burying Beetle (_Silpha atrata_) and larva.
]
Usually elongated, small (Fig. 70). The short truncated wing-covers
leave the whole of the abdomen exposed. The rove beetles resemble the
earwigs in their appearance and in a way they have of frequently lifting
up the hinder end of the body and turning it forwards. Tarsi
five-jointed, jaws strongly developed. The six-legged larvæ resemble
those of the ground beetles, but have a relatively large head. The
beetles live through the winter; the metamorphosis takes place in
autumn. Live on the ground under fallen leaves, also under the bark of
trees; in carcases. Some chiefly eat insects living in the soil and
noxious insects; others, dung and decomposing matter. (Species of
_Staphylinus_, and of _Ocypus_, e.g. _O. olens_, the =Devil’s Coach
Horse=.) Several are of service. A few devour the parts of plants.
_Anthobium torquatum_ is found in large numbers in the flowers of rape,
devouring the petals, stamens, and pollen.
Family: =Silphidæ= (_Burying_, or _Sexton Beetles_).
The antennæ either thicken gradually or have only the end-joints larger;
body flat; head projecting; tarsi five-jointed. The burying beetles and
their larvæ feed on dead animals. A few (sp. of _Necrophorus_) bury the
whole animal in the earth, and lay their eggs in it. Failing carrion,
some of them can live on vegetable food; these sometimes do harm. Others
prefer living insects and snails. They are of service in the economy of
nature by doing away with stinking bodies. The following are sometimes
harmful: =Black Burying Beetle= (_Silpha atrata_, Fig. 71), the larvæ of
which often do much damage in fields of beetroot; _Silpha opaca_ (=Beet
Carrion Beetle=), and _S. reticulata_, which, in the adult condition,
may do harm to several kinds of plants. Remedies need not be considered,
as it is only rarely they increase so largely as to make the supply of
carrion insufficient, and consequently attack plants.
Family: =Nitidulidæ= (_Shine Beetles_).
Small. Antennæ club-shaped, eleven-jointed. Tarsi five-jointed. A few
species live on carrion and on fungi, others under the bark of trees, a
few in flowers. To these last belongs the =Turnip Flower Beetle=
(_Meligethes æneus_); somewhat convex, elongated oval; shining metallic
greenish black, finely dotted. Occurs in the inflorescences of turnip,
rape, and allied species; also in the flowers of mustard, charlock, and
similar crucifers, and species of buttercup (_Ranunculus_). At the
beginning of spring, the turnip-flower beetle bores into the buds of
turnip, rape, etc., and, later on, attacks the flowers. It perforates
the petals, devours the stamens and pollen, and, lastly, the pistil. The
infested flowers wither. Three to four beetles are often found in a
single flower. The female soon lays her eggs, separately, in the ovary
of the flower. One to two weeks later the larvæ may be found in the
flowers, one or more in each. The larvæ, one-fiftieth of an inch long to
begin with, are, when ready to become pupæ, about one-fifth of an inch
long, cylindrical, yellowish white with blackish brown head; they have
three pairs of short thoracic legs, as well as a pair of caudal
pro-legs. Each segment of the body has two dark blotches on its upper
side. On an average, the larvæ reach their full size in four to five
weeks. They are first found at the bottom of the flower, where they gnaw
the stamens and ovary. They then wander from flower to flower, until
ready to become pupæ. If there are no more flowers in the neighbourhood
they attack the developing pods, first gnaw the green husk, then bore
through it and devour the young seeds. Become pupæ in the soil. The
beetle emerges after a fourteen days’ pupa rest. At least two, usually
three, sometimes four generations. _Remedy_: Rooting out charlock and
the species of buttercup. Selection of strongly growing varieties of
turnip, rape, etc., which blossom late (and therefore soon finish
blooming). Drill-culture.
Family: =Cryptophagidæ= (_Secret_-_eating Beetles_).
Very minute. Antennæ composed of eleven joints, of which the three last
form a club. Legs wide apart; tarsi five-jointed. Live in flowers,
fungi, dead parts of plants, under bark, in the earth, in humblebees’
and ants’ nests, etc. The =Beet Beetle= (_Atomaria linearis_) is
harmful: longish, egg-shaped, strongly convex; neck-shield as long as
broad. Brownish black or dark brown. In fields where beet is cultivated
for several years in succession, the beetles often increase in a
prodigious way. They attack the seedlings, and devour the base of the
stalk just below the surface of the soil, sometimes biting it half
through. The attacked seedlings often die even before the cotyledons
appear above the surface of the soil. Looking, therefore, in spring at
fields infested by the beet beetle, the seedlings will appear quite
normally developed in some few places, while in some other places there
may be no plants at all: in many spots, again, small plants will be seen
bearing only seed-leaves, withered and yellow. These cannot be pulled
out of the ground, for they break off at the place gnawed by the beetle.
It is often necessary to give two or three successive sowings, as the
young crop is attacked again and again. The larva of the beet beetle is
still unknown, though this undoubtedly develops in the beet-fields.
_Remedy_: Suitable rotation. When the conditions will not permit this,
the seed must be sown thickly, so that as many seedlings as possible may
remain sound, should the beetles exert their destructive influence in
the spring.
Family: =Lamellicornia= (_Chafers_).
[Illustration:
FIG. 72.—_a_, Antennæ of male; _b_, of female Cockchafer.
]
Body strong, stout (Fig. 65). The first joints of the antennæ have the
usual shape; the last, three to seven, are very short, but broadened out
on the inner side into leaf-like appendages, so that the end of the
antennæ is fan-shaped (Fig. 72). The little leaves are laid together
when at rest, so as to form a club-shaped thickened end; in flight, and
when the attention of the beetle is excited, they are spread out like a
fan. Legs strong; feet five-jointed. Flight rapid, somewhat awkward.
Larvæ thick; body cylindrical, but curved; head hard, brown; rest of the
body thin-skinned and yellowish white. The first three segments of the
body bear legs. The curved larvæ can move about in the soil, but not on
the surface. The beetles and larvæ devour vegetable substances; a
comparatively small number of species feed on dung.
[Illustration:
FIG. 73.—_a_, abdomen of Common; _b_, of Horse-chestnut Cockchafer.
]
The =Common Cockchafer= (_Melolontha vulgaris_) will serve as a type of
the lamellicorns (Fig. 65). The last segment of the body forms a
gradually tapering process. The club of the antennæ with seven large
leaflets in the male, and six smaller leaflets in the female (Fig. 72).
Head, neck-shield, entire ventral surface, and legs, black; although
these parts, with the exception of the head, may be reddish brown. Many
specimens are thickly clothed with numerous white hairs; others are
almost hairless. The beetles usually appear during May, but sometimes by
mid April, and sometimes not till the beginning of June. In the evening
they leave the soil and seek the neighbouring trees. They devour the
leaves and especially the buds of oak, horse-chestnut, beech, poplar,
willow, cherry, and other forest and fruit trees, but spare the lime and
generally the morel cherry. Of coniferous trees it only devours the
needles of larch and the young shoots of pine. Among cabbage-like plants
it only devours rape. In “chafer years” the cockchafer becomes a
veritable scourge to the farmer. For the purpose of laying her eggs
(about forty in number), the female selects by preference a fertile soil
rich in humus, but will also put up with a dry sandy soil. The grubs
devour the grass and clover-roots in meadows, and, in cultivated fields,
the roots of grain-plants, peas, and beans, rape, cabbage, etc., also
turnips and potatoes; in gardens the roots of many vegetables and
flowers, and, in particular, the underground parts of strawberry plants.
If, on poor sandy soil, they can get nothing else, they devour the bark
of oak and fir. Cockchafers take three to four years for their
development: four in England, North Germany, and Central Germany; three
in South France, Switzerland, the Rhine district, and Holland. In
regions where the insect is abundant, every third or fourth year is a
“chaferyear,” when the beetles appear in millions, while scarcely a
cockchafer can be found in the intervening years. In districts less
infested there is not the same marked distinction. It therefore appears
that cockchafers and their larvæ are to be reckoned as injurious
insects: their occurrence, however, is local. _Natural enemies_: moles,
shrews, bats, foxes, crow-like birds, starlings, sparrows, owls, and the
large species of ground-beetle. Winter floods do no harm to the grubs,
which are then deep in the ground,—but this is not the case with floods
occurring in summer, when they are near the surface eating the roots of
the plants. _Remedies_: Collecting the grubs turned up during ploughing.
Catching the cockchafers; this is very expensive, since it has to be
done very energetically if most of them have left the pupastage. A part
of the expense may, however, be recouped by using the cockchafers as
manure.
The =Horse-chestnut Cockchafer= (_Melolontha hippocastani_) has a short
slender caudal process, somewhat broader at the tip (Fig. 73). Its
habits are in no way different from those of the preceding species.
The =Buckwheat Beetle= (_Phyllopertha horticola_), one-third to
one-fifth of an inch long, without a caudal process. Shining blackish
green, with yellowish brown elytra. Dark-coloured specimens are also
found. The beetles appear in June; in some years they occur, like
cockchafers, in large numbers. Habits of the beetle and of the small
grub not markedly different from those of the cockchafer.
The =Rye Chafer= (_Anisoplia fruticola_), somewhat larger than the
buckwheat beetle, in other respects very like it, but with a snout-like
projection of the thickened skin of the head. Dark bronzy green, whitish
on the under side. Wing-covers yellowish brown. On poor sandy soil, on
the flowering ears of rye. The beetles gnaw the flowers.
[The =Garden Chafer= (_Anisoplia horticola_) is closely related to the
preceding. The grub is very harmful to pastures.]
Family: =Elateridæ= (_Click Beetles_).
[Illustration:
FIG. 74.—The Skipjack (_Agriotes lineatus_): 1, magnified larva, below
it the under side of the tip of the abdomen and the larva, natural
size; 2, the beetle; 3, under side of the head of the larva,
strongly magnified. _a_, maxilla; _b_, lower lip; _d_, labial palp;
_e_, _k_, inner and outer maxillary palps; _f_, antennæ.
]
The Click Beetles (Fig. 74) are longish, of equal breadth all along,
tolerably blunt at the hind end. Neck-shield strongly developed. Antennæ
“serrated,” _i.e._ made up of three-cornered joints. Feet five-jointed.
Looking at the under side a spine may be seen on the hinder margin of
the prothorax (Fig. 75, _b_), and on the mesothorax (_c_) a furrow which
receives the spine when the body is extended, but the spine is drawn out
of it if the prothorax and mesothorax are lifted up from anything they
happen to rest on (Fig. 75). A skipjack that has fallen upon its back
first draws its antennæ and legs close to its body, and then bends this
in such a way that the head and prothorax make an angle with the rest of
the thorax and the abdomen. In this way the junction of the prothorax
and mesothorax is lifted up, and the spine drawn as far as possible out
of the furrow. As soon as the beetle has taken up this attitude, it can
spring back into its usual position by lifting the two ends of the body
and pressing the spine forcibly back into the furrow, whereby it is
jerked against the ground with such a shock that its elasticity makes it
spring into the air, where it turns round and comes down again ventral
side below. The larvæ (“wireworms,” Fig. 74, 1) are like meal-worms,
elongated, always flattened on the ventral side, and sometimes on the
dorsal side as well. The head is dark brown, the twelve remaining
segments of the body yellow to yellowish brown; the first three segments
of the body bear three pairs of very small legs; the last segment has a
pair of caudal pro-legs.
[Illustration:
FIG. 75.—A Skipjack lying on its back and about to spring up. _a_,
head; _b_, spine of the prothorax; _c_, mesothorax; _d_, metathorax;
_e_, abdomen.
]
[Illustration:
FIG. 76.—Grain-plants sown deep and shallow; a wireworm is devouring
the underground part of the stem of the first.
]
Many species of click beetle are quite harmless, since they only devour
decaying vegetable matter, either in humus or in the rotting substance
of dying trees. There are also species, however, the larvæ of which feed
on the living roots of plants. The wireworms of _Lacon murinus_, which
are tolerably thick and have a flattened tip to the abdomen, devour the
roots of fruit trees, rose-bushes, various vegetables (lettuce, cabbage,
onions, turnips) and flowers; they are principally to be found in garden
soils rich in humus. The relatively small hairless wireworms which do
great damage, especially to grain-plants, but also to potatoes, carrots,
turnips, rape, hops, and almost all the plants of our arable land,
belong to _Agriotes lineatus_ or _A. obscurus_; the larger and more
hairy wireworms destructive in cultivated land almost all belong to
_Athous hæmorrhoidalis_ or a related species. The species named above
also do much damage in meadows and grass land. Those fields are most
infested which bore grass or clover the preceding year. Wireworms are
usually more destructive in dry soil than in wet. They devour all
underground parts, but specially prefer fleshy organs (potatoes,
turnips), as well as the underground stem-parts of grain-plants, working
themselves up from the soil into the inside of the lower part of the
haulm, where they destroy the plant by gnawing its base. They also often
destroy, in young grain-plants, the region of the stem which extends
from the remains of the seed to the surface (Fig. 76, _left_). In both
cases the plant is killed by the wireworms; the injuring of the roots is
less fatal. It is obvious that in shallow sowing only a small piece of
underground stem is exposed to the attacks of wireworms, in deep sowing
a much larger piece; besides this, a plant which has been sown shallow
develops earlier a strong mass of roots, and in its young state can
therefore offer a greater resistance to the destructive influence. Since
wireworms require four or five years for their development, the same
field is infested by them the whole year. The greatest damage is done in
spring and autumn. When wireworms have gnawed into the lower part of the
haulm, the lower leaves first turn yellow, and the death of the whole
plant soon follows. _Remedies_: Repeated ploughing of fields infested by
wireworms, so that rooks, starlings, wagtails, gulls, etc., can devour
them. Perhaps, too, many larvæ are frozen. Sowing the seed as shallow as
possible on infested fields (Fig. 76). Waste potatoes may be used as a
means of drawing them from the crop.
Family: =Curculionidæ= (_Weevils_).
Most species are small. Head lengthened into a proboscis (Fig. 79, 3);
the jaws are found at the front end of the proboscis, the eyes at its
base. The antennæ, which in most species are bent like a knee, and are
always thickened at the tip, are attached to the front end, middle, or
hinder end of the proboscis. The wing-covers usually extend to the tip
of the abdomen, and clasp it in several species. Feet four-jointed.
Weevils are mostly sluggish; many kinds do not fly at all; others only
during the breeding season. When disturbed they let themselves fall to
the ground as if dead. Almost without exception the females lay their
eggs within plants, boring a hole by means of their proboscis, and
shoving in the egg. The whitish larvæ (Fig. 66) are more or less curved
and limbless, with hard brownish heads.
[Illustration:
FIG. 77.—The Bean Beetle (_Bruchus rufimanus_) and beans gnawed by it.
]
The =Seed Beetles= (_Bruchus_) have a very short snout. Body short,
thick-set, almost four-cornered. The wing-covers leave the hinder part
of the body exposed. The female lays her eggs in the seeds of leguminous
plants. The larva hollows out one or several, becoming a pupa in the one
last inhabited. Here belong the =Pea Beetle= (_B. pisi_), the two =Bean
Beetles= (_B. rufimanus_ and _B. granarius_), of which the last-named
also lives in vetches and chickling peas, and the =Lentil Beetle= (_B.
lentis_). The =Pea Beetle= (_B. pisi_) is black, with brown hairy
covering flecked with white. Like all other species of seed beetle, it
becomes a pupa in the last seed inhabited by the larva, and the pupa
changes into a beetle in autumn. A pea inhabited by such an insect can
be recognized by a black translucent patch, since the beetle has become
a pupa immediately under the seed-coat. Late the following spring the
beetle crawls out. As the beetles are usually still in the peas at the
time of sowing, the process brings them into the fields. Later on, when
the beetles crawl out, they lay their eggs in the ovaries of the flowers
of the pea-plants, which have meanwhile developed. The _remedies_ are,
consequently,—late sowing of the peas, or killing the beetles in them by
exposure (for two minutes) to a temperature of 122° Fahr., or for ten
minutes to sulphur dioxide fumes in a closed space. The remaining three
species of Bruchus have the same habits as the bean beetle, but the
insect often creeps out much earlier, so that the seeds do not require
treatment.
[Illustration:
FIG. 78.—Attacks of Pea Weevil: _a_, _b_, on pea leaves; _c_, on a
bean leaflet.
]
The =Pea Weevil= (_Sitones lineatus_). Longish, with grey scales on a
black background. Neck-shield with three longitudinal streaks,
wing-covers with dotted lines. These weevils appear at the first
beginning of spring on peas, field and garden beans, clover, and
vetches. They gnaw the leaf-margins of the tender plants, and always in
such a way as to present a toothed appearance (Fig. 78). It often
happens that in a large field one can scarcely find a pea-leaf with
uninjured margin. When the plants are somewhat grown the damage done by
the weevils is of no further importance; but if the plants, when still
very young, are prevented from growing rapidly by reason of rough cold
weather or unfavourable conditions of soil, while at the same time the
weevils continue their attacks, the small leaves will be completely
destroyed, and the plants will perish. The larvæ gnaw the roots of the
plants infested by the weevils. _Remedy_: rational rotation.
The =Mouse-tooth Weevils= (_Baris_, or _Baridius_). Small, tolerably
elongated weevils with fairly long neck-shield (Fig. 79). Develop in
cruciferous plants. The =Rape Mouse-tooth Weevil= (_B. chloris_).
Shining green. Leaves in spring its hiding-place in the soil; the female
then lays her eggs in the leaf-axils or stem of rape or turnip. The
larva eats out passages in the stem and branches; in July it becomes a
pupa in the inside of the stem; in late summer the beetle appears, and
quickly creeps into the soil. _Remedy_: Pulling up and burning the rape
and turnip stubble, which harbours the weevil. The =Pitchy Mouse-tooth
Weevil= (_B. picina_), one-sixth of an inch long, shining black. Similar
habits to the previous species; but lives exclusively in headed cabbage
and cauliflower, never in rape and turnip. The =Cress Mouse-tooth
Weevil= (_B. lepidii_), black with blue or greenish-blue back,
one-eighth of an inch long. Lives in the stems of cauliflower and garden
cress.
[Illustration:
FIG. 79.—Mouse-tooth Weevil (_Baridius chloris_). 1, _larva_; drawn on
the left, natural size,—above, the magnified head: 2, _pupa_,
magnified: 3, _beetle_; drawn of the natural size above: _a._, eye;
_g_, antennary groove with antenna not drawn back.
]
[Illustration:
FIG. 80.—Turnip Gall Weevil (_Ceutorhynchus sulcicollis_).
]
The =Gall Weevils= (_Ceutorhynchus_) are very small beetles with
thick-set bodies. In a state of rest the proboscis is folded back into a
ventral furrow, situated between the fore-hips. They are black, and
thickly covered with grey hairs. Live on cruciferous plants. The =Turnip
Gall Weevil= (_Ceutorhynchus sulcicollis_), one-eighth of an inch long,
dull black, with many grey hairs on the ventral side and few on the
dorsal side. The deeply pitted neck-shield has in its centre a
well-marked longitudinal furrow. Wing-covers deeply furrowed. The beetle
appears in April, and gnaws the flowers and shoots, but can scarcely be
considered as harmful. In late summer or autumn, after the sprouting of
the winter rape, the female bites into the root immediately under the
surface of the soil, or into the lower parts of the stem, so as to form
a hole in which she lays one or two eggs. As the larva begins to
develop, the surrounding parts of the stem or root grow into a gall-like
swelling (Fig. 80). At the beginning of spring the developed larvæ creep
out, and become pupæ in the soil; in April the beetle appears. If the
Ceutorhynchus galls are only present in small numbers they damage the
rape plants only to a small extent, but when ten to twelve are found in
one plant the roots grow crooked, and remain short, and consequently the
growth of the overground parts is detrimentally affected. Ceutorhynchus
galls are found, not only on rape, but also on the different kinds of
cabbage, and on turnip plants. In the last case they often occur in such
numbers that the turnips do not develop at all, and the overground parts
also remain small. There is a similar form (_C. assimilis_), as large as
the preceding species, but somewhat slimmer, and, on account of greater
hairiness, greyer. Appears in spring on flowering rape and several kinds
of cabbage, as well as on similar cruciferous plants. It is harmful
because the beetles gnaw the buds and flowers, and the larvæ feed on the
seeds within the pods. The attacked pods ripen early, and open so that
the larvæ fall to the ground, where they become pupæ. Usually only a
single larva is found in each pod. The =Rape Gall Weevil= (_C. napi_),
somewhat larger than the two preceding species, has a neck-shield which
projects strongly forward like a collar, and is marked by a median
longitudinal furrow. It is covered with yellowish-grey hairs. At the
time when rape blooms it appears upon the flowers. The female lays her
eggs singly in a hole previously bored in the stalk by her proboscis;
during spring and early summer the larva eats out the stem, which turns
brown inside, and becomes diseased or even dies.
Family: =Chrysomelidæ= (_Leaf Beetles_).
[Illustration:
FIG. 81.—Potato Beetle (_Chrysomela decemlineata_).
]
Small, generally thick-set beetles, arched on the upper side, with
eleven-jointed antennæ thickening somewhat towards their tips, and
four-jointed feet. The first joints of the feet are covered with
felt-like hairs on their under sides (Fig. 81). The larvæ have three
pairs of thoracic feet, and, in addition to this, there are in most
species a pair of caudal pro-legs. Live in the inside parts of plants
(stems, leaves), and are usually elongated and yellowish white; those
which live on the outside of plants are more convex, shorter, and
thicker, more or less hairy, often of a striking colour, and always with
dark spots. The beetles eat leaves; the larvæ feed upon parts of the
same plants, sometimes living outside upon the leaves, or it may be
excavating channels in the inside of a leaf or of the stem. Most leaf
beetles lay many eggs, and in many species there are several generations
annually. The plants attacked by them are often stripped quite bare.
Here belongs the blue =Alder Leaf Beetle= (_Galeruca alni_), the =Poplar
Beetles= (_Chrysomeli populi_ and _C. tremulæ_), the =Asparagus Beetles=
(_Crioceris merdigera_ and _C. duodecimpunctata_), etc. Of species
injurious agriculturally, I will first mention the =Colorado= or =Potato
Beetle= (_Chrysomela decemlineata_). This beetle originally lived in the
west of the United States on wild solanaceous plants; but as soon as
potato culture extended to the west the beetles also attacked potato
plants. As soon as the insects had spread to this plant they began to
appear in great numbers owing to their very great powers of
reproduction; and they quickly spread from one field to another, always
going further and further east. 1859 was the first year when they became
notorious as pests, and, since they first appeared as such in the State
of Colorado, the insect received the name “Colorado Beetle.” In a short
time the beetles spread to the east, especially to places where potato
culture was carried on; in 1865 they crossed the Mississippi, and in
1870 they were already spread over the states of Indiana, Ohio,
Pennsylvania, Massachusetts, and New York. They were soon found in all
the eastern states, and European farmers began to be alarmed. In most of
the countries of Europe police regulations were made for the purpose of
preventing the introduction of the unbidden guests. Colorado beetles
have indeed been brought several times to Germany on board ship, but in
almost all cases the pests so introduced have been recognized and
caught. Twice during 1877 they were able to increase (Mulheim,
Schildau), and the same thing has happened once at a more recent date
(Torgau); but the vigorous action of the authorities quickly
exterminated the beetles.
[Illustration:
FIG. 82.—Colorado Beetles: _a_, eggs; _b_, _c_, _d_, younger and older
larvæ; _e_, pupæ seen from the ventral side and from the dorsal
side.
]
Beetle (Fig. 81), half an inch long, dusky yellow, with five
longitudinal black streaks on each wing-cover, and black markings on the
neck-shield. Larva (Fig. 82), half an inch long, thick, fleshy; legs
short and weak. Orange-yellow, with shining black head, and with black
spots on the body segments. The younger larvæ are darker, almost blood
red. When the young potato plants come up, the beetles which have
survived the winter creep out of the soil and devour the margins of the
young leaves. The female lays her yellow eggs (700 to 1200?) in heaps on
the leaves (Fig. 82, _a_). After a week the larvæ appear, and carry on
the work of the beetles. They attain their full development in seventeen
to twenty days, become pupæ in the soil, and the beetles of the second
generation make their appearance in the middle of June. Still a third
generation may appear the same year. Since a considerable time elapses
between the laying of the first and second batches of eggs, one usually
sees eggs, larvæ, pupæ, and beetles at the same time. Entire potato
fields are eaten bare by the beetles and their larvæ, the formation of
the potatoes being quite prevented. _Remedies_: Energetic measures must
be taken on the first appearance of the beetle in any district. Where
possible, all the beetles and larvæ must be collected, the plants being
dug up and destroyed with the beetles, pupæ, larvæ, and eggs adhering to
them. Petroleum must then be poured over the whole field and set on
fire, so as to destroy any insects which may be hidden in the soil.
Spraying the attacked plants with Schweinfurt green.
[Illustration:
FIG. 83.—The Cloudy Tortoise Beetle (_Cassida nebulosa_).
]
The =Cloudy Tortoise Beetle= (_Cassida nebulosa_)—Fig. 83. One-fifth to
one-fourth of an inch long; the broad neck-shield projects in front over
the small head. The wing-covers, too, are much broader than the body of
the animal; they are longitudinally ribbed. Dorsal side reddish brown,
in young individuals greenish; always with black spots. Ventral side
black. Larva elongated oval, yellowish green. Segments of the body beset
with thorn-like structures bearing lateral branches; the last segment
possesses a “tail-fork,” which the larva usually carries bent over its
back and on which it heaps up its dung. The beetles which have survived
the winter usually attack in spring only wild goose-foot and orach
plants, on which they lay their eggs in heaps. The larvæ quickly appear,
and to begin with chiefly keep to the under sides of the leaves. They
are sluggish, grow quickly, and devour the leaf substance; when fully
developed they cement themselves to a leaf and become pupæ. In June the
beetles of the second generation appear, which again lay their eggs on
the leaves. In favourable weather there may be even a third generation.
In many it happens that the beetles of the second generation migrate to
beet or mangold plants, sometimes damaging them to a very great extent.
_Remedy_: Rooting out species of goose-foot or orach.
The =Earth Fleas=, or =Flea Beetles=, are all small leaf beetles with
the power of springing, and therefore provided with thick thighs. Here
belong:—
[Illustration:
FIG. 84.—The Rape Flea Beetle (2) with hind-leg of the same; larva (1)
and its head.
]
The =Rape Flea Beetle= (_Psylliodes chrysocephalus_)—Fig. 84.
Egg-shaped. Hind feet not inserted at the ends of the shanks, but higher
up. The first joint of the foot is as long as the others put together.
The rest of the hind foot is bent in a knee-like way on the first long
joint. Shining blackish brown or blackish green, rarely brownish. Larva
one-fifth to one-fourth of an inch, dusky white; head, neck-shield, and
last segment of the body blackish brown. In spring and during the entire
summer the beetles are found upon the plants of winter rape. Although
they gnaw the leaves and the immature shoot the damage caused is small.
In late summer or autumn the female beetles lay their eggs separately at
the bases of the leaf-stalks of the young winter rape plants. The larvæ
which emerge bore into the leaf-stalk, and eat it completely out during
autumn, winter, and spring, so that the leaf dies. Since the eggs are
laid separately the larvæ do not all develop at the same time in the
spring. In spring many larvæ eat their way from the leaf-stalks into the
still very short stem, which consequently ceases to develop. It often
happens that most, or even all, of the plants in a rape field are
withered; on poor soil the whole crop must be at once ploughed up; but
on fertile soil the plants often develop much better than one would
believe. Plants whose stem has been killed in the winter while still
short may develop a few (3 to 5) branches from buds situated near its
base, but these usually remain small, and do not yield a large crop. The
beetles, appearing in spring, lay their eggs on the lower leaf-stalks of
the rape, either on the old plants of winter rape or young plants of
summer rape. In the latter case the summer rape is quite spoilt in the
same way as the winter rape during the previous winter. In the former
case the larvæ eat out the lower part of the leaf-stalks, and make their
way into the stem, hollowing it out at a definite spot in such a way
that it is no longer able to hold itself up, especially when the shoots
and seeds develop. The stems bend and become kneed, sometimes to such an
extent that the rape field looks as if persons or cattle had been
running about in it in all directions, and treading everything down.
Meanwhile the larvæ bore their way out of the stem, and become pupæ in
the soil. In late summer the beetles appear, and once more lay their
eggs on the leaf-stalks of the winter rape. There are, therefore, two
generations annually. _Remedies_: Never sow summer rape after winter
rape which has been destroyed by the beetle and ploughed up. Temporary
limitation of rape culture.
The =Cabbage Flea Beetle= (_Haltica oleracea_), one-fifth to one-sixth
of an inch long, longish oval, dark green, metallic sheen. The hind legs
do not possess the peculiar features of the rape flea beetle (p. 114).
Larva one-fifth to one-fourth of an inch long, greyish black, with
bristly hairs, and with two rows of shining black warts. The beetles
attack, in the spring, chiefly cabbage, rape, radishes, horseradish; but
do not spare other plants (_e.g._ peas and beets) as well. Seedlings are
chiefly attacked, and in all cases only young plants are devoured. Since
both seed-leaves and terminal buds are eaten, much damage is done,
especially during continuously dry weather. It must often happen that
the beetles wander away, to find other species of plants for the purpose
of egg-laying; so that it is exceptional to find the larvæ upon species
of cabbage. These larvæ are much less injurious than the beetles, since
they usually only prey upon mature plants. In their youngest condition
they are found in groups, feeding upon the leaves; this results from the
eggs being laid in little heaps. Later on, they wander away from one
another. In favourable weather they are fully grown in six weeks, and
several generations may succeed one another in the same year.
_Remedies_: Destruction of the weeds which attract the beetles
(charlock, shepherd’s purse, yellow rocket, treacle mustard, etc.) Good
preparation of the soil, suitable manuring and drill culture, since
these bring about a more rapid growth of the plants. Thick sowing (but
not too thick), so that, even after the destruction of many seedlings, a
sufficient number may remain. Moistening the fields by means of
water-carts or sprayers. In garden-beds twigs are laid down, by which
the seeds are protected against birds and the seedlings against flea
beetles. “Flea-beetle machines,” consisting of a board smeared with tar,
which is drawn across the field, so that the frightened beetles spring
up, and remain hanging in the sticky substance. After rain, or when dew
is still clinging to the plants, they should be strewed with powdered
fowls’ dung, pigeons’ dung, or horse dung, wood-ashes, road-dust,
powdered lime, coal-ashes; or the plan of sprinkling with a decoction of
wormwood may be adopted.
The =Turnip Flea Beetle=, or =Turnip Fly= (_Haltica nemorum_), one-tenth
to one-eighth of an inch long, egg-shaped, black, with longitudinal
streaks of a sulphur yellow colour on the thickly pitted wing-covers.
Larva one-fifth of an inch long, yellowish white, with dark brown head,
neck-shield, and last body segment. The adult beetles have the same
habits as in the preceding species; they also do damage in the same way,
and attack the same plants, especially in the seedling condition. The
female, however, does not lay her eggs in heaps, but separately on the
leaves, and always on the under side. The larva bores into the leaf, and
digs a passage, which, like the animal inhabiting it, is at first small,
but gets gradually larger. In fine weather the larva is fully developed
in a week. It then pierces the skin covering the under side of the leaf,
falls to the ground, and becomes a pupa. Several generations may appear
every year, if the weather is favourable (dry). This species is quite as
harmful as the preceding, chiefly in the mature condition. _Remedies_:
Compare the preceding species.
Family: =Coccinellidæ= (_Lady-birds_).
Hemispherical; upper side convex; under side flattened. Head small,
retractile. Antennæ, eleven-jointed, thickened at their tips. Legs
short; feet apparently three-jointed—in reality four-jointed, the second
joint, however, being very small. Colour, usually variegated; many
species black with red, or red with black spots. When grasped, they let
a yellowish, unpleasant-smelling fluid escape from the abdomen. The
blunt, four-cornered, usually variegated pupæ hang on the leaves. The
fully developed larvæ are longer than the beetles. They closely resemble
those of the leaf beetles, but are not so thick-set, and their longer
legs stick out more laterally. They are covered with warts and little
spines (Fig. 85). The larvæ and beetles of most species feed chiefly on
aphides and shield-lice; they are therefore of use, and this is
especially true of the exceedingly ravenous larvæ. The larvæ of the
Seven-spotted and Two-spotted Lady-birds, in particular (_Coccinella
septempunctata_ and _C. bipunctata_), are found in large numbers among
aphis colonies. The yellow eggs are laid in heaps.
[Illustration:
FIG. 85.—The Seven-spotted Lady-bird (_Coccinella septempunctata_):
larvæ, pupæ, beetles; all natural size.
]
SECOND ORDER: =Orthoptera= (STRAIGHT-WINGED INSECTS).
Insects with biting mouth-parts and incomplete metamorphosis (p. 89).
Four wings, of which the anterior are usually harder than the posterior;
hind wings membranous, broader than the fore wings, and folded like a
fan. The Orthoptera feed entirely, or almost so, upon vegetable
substances. To this order belong:—the =Earwigs= (_Forficulariæ_), which
feed on sweet fruits and flowers, and are sometimes very injurious; the
=Cockroaches= (_Blattariæ_), which do much damage to provisions in
kitchens, stores, and on board ship; the =Grasshoppers= (_Acrydites_),
to which, besides the =Migratory Grasshopper= (_Acrydium migratorium_)
Fig. 62, various species of meadow grasshoppers belong, which are quite
harmless; the =Locusts= (_Locustidæ_), to which the well-known =Green
Locust= (_Locusta viridissima_) belongs; and the =Crickets=
(_Gryllidæ_), to which belong, among others, the =House Cricket=
(_Gryllus domesticus_), the quite harmless =Field Cricket= (_Gryllus
campestris_), and the =Mole Cricket= (_Gryllotalpa vulgaris_).
The =Migratory Grasshopper= (_Acrydium migratorium_).
1⅗ to 2⅗ inches long; spread of the wing, on the average, 2½ inches.
Greenish grey. Under side flesh colour. Wing-covers brownish, darkly
flecked. Colour very variable (Fig. 62). Excessive multiplication and
migrations of this insect often take place in South Russia and Turkey;
but they may also appear in Central Europe. In North Germany, for
example, the following years of this century were “grasshopper years:”
1803, 1825–27, 1853, 1875–76. In many cases the appearance of swarms of
grasshoppers in Central Europe is due to migration from Russia and
Hungary; but it also often happens that the insects which appear in such
large numbers have been bred in the places where they are found. Since
the female lays, on the average, 150 eggs, excessive increase may take
place in any country to which they are indigenous—and therefore in
Central Europe. It appears, however, that a large number of grasshoppers
are usually killed by their natural enemies, such as cold and damp
weather. Excessive increase may, however, take place in exceptionally
favourable years; and since the larvæ, which are incapable of flight,
devour everything available, the mature insects developed from them are
forced to migrate. Where they descend they destroy everything they find
in the fields. _Remedies_: Destruction of the longish eggs, which are
laid in heaps in the earth of fallow ground and meadows. In all those
places where dead insects are found in large numbers on the ground many
eggs will also be discovered, for the insects keep on laying till they
sink down dead in the place where the last heap of eggs was deposited.
Such places should be dug or ploughed, and the eggs, which are present
in thousands, either collected or else searched out by pigs, ducks,
geese, and fowls, which have been driven to the spot. Destruction of the
young animals while still incapable of flight. Working the soil with
harrows, rollers, and cultivators will be effective here. The adult
grasshoppers must for the most part be destroyed with fire. [Heaps of
straw and brushwood are soaked with paraffin and then set on fire.]
The =Mole Cricket= (_Gryllotalpa vulgaris_).
Body stout and flattened. Antennæ, palps, and tail-filaments very long.
Fore legs broad, modified into true “digging legs,” superficially
resembling the feet of a mole. Fore wings broad, but short, leathery. In
a state of rest, the hind wings lie on the back, like a couple of tails.
Colour dark brown. Principally occurs on peaty soils mixed with sand or
clay, also on all soils which have become of firm consistency by the
application of much manure. Their presence is therefore local. Very
early in the year the mole-cricket leaves its winter hiding-place, and
begins to make its passages near the surface. Where the female makes her
nest the passage turns downward a little. The nest is 1⅗ of an inch in
diameter, and its walls are compacted by the pressure of the hard body.
The number of eggs is from 200 to 250; they are laid in lots with a few
intermediate spaces. The young creep out in the spring, and are
wingless. To begin with, they are white, but quickly become brown. The
mother guards her young very carefully. These grow tolerably fast, and
first begin to lead an independent life after the second moult. In
October and November they undergo a third moult. Then, still in a
wingless condition, they hide themselves, and do not moult again till
April or May, when the wing-cases appear; while after the fifth moult
(May, June) the mole-cricket becomes an adult insect, capable of
reproducing. This insect is found in cornfields, gardens, grassland, and
meadows, also in orchards and woods. It gnaws the roots of all kinds of
plants, and often effects great damage in this way. The mole-cricket is
also harmful on account of its passages, which are dug close to the
surface. In this way it lifts young plants out of the soil; while older
plants are killed, both by its gnawing and by its digging. Such plants
can often be pulled up by grasping the leaves. All the plants wither in
the place where the nest is found. Dry, cold winters kill almost all the
mole-crickets; much drought in summer and also continuous wet are
unfavourable to them. _Enemies_: moles, rooks, etc., butcher-birds,
starlings, and the larger ground beetles. _Remedies_: Destruction of the
nests, in June, to begin with, but also to be continued later. In those
parts of a field where the plants are yellow or withered in a large
circular patch (some 39 inches in diameter) the nest is felt for with
the finger, and carefully lifted up, so that the eggs do not fall out.
Mole-crickets can also be caught by means of flower-pots. The apertures
in the bottoms of these are stopped with corks, and they are then sunk
in the soil with their mouths on a level with the mole-cricket passages;
they thus serve as pitfalls, from which the insects cannot escape. If
during winter little heaps of horse dung are placed on the ground, the
insects creep into them for the sake of the warmth, and can thus be
collected and killed.
THIRD ORDER: =Neuroptera= (NET-WINGED INSECTS).
Insects with biting mouth-parts and four similar membranous wings, with
numerous veins arranged in a net-like manner. The metamorphosis is
either incomplete (p. 89: dragon flies, may flies, book lice), or
complete (p. 89: ant lions, lace flies, snake flies, scorpion flies,
caddis flies). The indigenous forms, with the single exception of book
lice, feed upon animal food, usually on the juices of other insects.
Several of them are tolerably useful in this way.
The =Dragon Flies= (_Libellulidæ_) fly about incessantly from place to
place on bright warm days, and catch a large number of insects,
especially butterflies and flies, among which are many that are harmful.
The larvæ live in water, and feed on insects and such small deer, which,
however, are of no importance to forestry or agriculture. They also
devour fish-spawn, and may therefore be injurious in that way.
[Illustration:
FIG. 86.—The Common Lace Fly (_Chrysopa vulgaris_): _a_, eggs; _b_,
the larva; _c_, cocoon; _d_, pupa contained in the same; _e_, open
cocoon; _f_, adult insect; _a_, _c_, _e_, natural size; _d_,
enlarged and natural size; _b_ and _f_ enlarged.
]
The =Lace Flies= (_Hemerobidæ_) when at rest are covered as with a roof
by their fore and hind wings, which are almost alike, clear as glass,
and finely veined. Head tolerably large, eyes large, abdomen elongated
and slender. The extremely rapacious larvæ (Fig. 86, _b_) feed on the
juices of the bodies of other insects, which they suck up by means of a
pincer-like organ situated on either side of the mouth. The two pincers
are perforated, and the tubes open on each side into the gullet; the
body juices of the insects attacked thus flow into the gut of the larva.
This is strongly built, and always much thicker and larger than the
adult insect. Metamorphosis complete. Three genera belong to the lace
flies:—
1. The delicate greenish, or greenish yellow, illsmelling =Gold-eyed
Lace Flies= (_Chrysopa_), the larvæ of which chiefly feed on plant lice
(a few species on caterpillars, also, and other small insect larvæ).
2. The =Aphis Lions= (_Hemerobius_: _H. hirtus_, with hairy veins on the
fore wings; _H. dipterus_, with hind wings almost entirely absent), the
larvæ of which also feed on aphides, and make a case from their
sucked-out skins.
3. The =Ant Lions= (_Myrmeleon_), of which the fat, thick-set larvæ,
which have a large head and strong grasping pincers, dig out in the sand
funnel-shaped holes, at the bottom of which they hide, lying in wait for
ants and the like, which step on the edge, when the sand gives way and
causes them to fall in. The species of the first two genera are of
service as destroyers of aphides; the ant lions are of no importance.
The =Scorpion Flies= (_Panorpatæ_) have attached to the head a kind of
proboscis, the upper side of which is formed by a prolongation of the
forehead, and the under side by the maxillæ and lower lip, while the
upper lip and mandibles are hinged on at its tip. Here belongs the
slender-bodied =Scorpion Fly= (_Panorpa communis_), an insect found in
May, and again in July or August, on the leaves of trees and shrubs,
when it is sunny. While the abdomen of the female ends in an ovipositor,
it bends upwards in the male, and terminates in a pincer-like organ;
hence the name “scorpion fly.” Wings flecked with brown. Scorpion flies
catch on the wing a very large number of butterflies and moths, and are
therefore useful to some extent.
FOURTH ORDER: =Hymenoptera= (MEMBRANOUS-WINGED INSECTS).
Upper lip and mandibles short; the latter used for biting. Maxillæ
loose-jointed, so that they can be stretched out considerably; elongated
in those which lick the juices of flowers. In the last-named forms the
larva’s lips are still more elongated, and may even form a tongue or
proboscis-like organ, which may bear lateral appendages (“secondary
tongues”). Wings, four, all membranous, with relatively few veins (Figs.
61, 90). Metamorphosis complete; larvæ very various; pupæ free (p. 93).
The female usually possesses an ovipositor, the structure of which
varies a great deal, and which serves in many species, not only for
egg-laying, but also for protection (digging wasps); in others
exclusively for offence or defence (“stings” of bees and wasps), while
the same opening serves for the passage both of eggs and excrement. The
abdominal glands, secreting a sticky substance by which the eggs are
attached, are modified into poison-glands in those Hymenoptera which
possess a sting. In those forms where the ovipositor is not modified
into a sting, it is used for piercing, biting, or sawing. The
Hymenoptera with saw-like ovipositor first make an opening in wood or in
a leaf by means of the saw-teeth in its edge, and then lay an egg in
this hole.
[Illustration:
FIG. 87.—Head of Honey Bee. _A_, compound eyes; _a_, simple eyes; Fh,
antennæ; _Z_, tongue (under lip); _b_, labial palps; _Fz_, elongated
maxillæ; the mandibles and upper lip remain short.
]
Many Hymenoptera (all digging wasps, gold wasps, ichneumon flies, and
gall flies—several true bees and wasps) live alone, or in pairs. Others
form colonies, in which division of labour is always so far carried out
that there are _reproductive individuals_ and _workers_. The former
(males and females; in colonies of bees—“drones” and “queen”) are only
present in small numbers in any particular colony. They live merely for
the perpetuation of the species. At most the males seek their own food,
while the females are usually fed by the workers. Workers, on the other
hand, are individuals in which the (female) reproductive organs remain
in a low state of development, so that they are sterile. They seek food
for the larvæ, and usually for the adult reproductive individuals as
well. They also wage war against strange intruders.
Family: =Apidæ= (_Bees_).
The bees, by means of their very much elongated mouth-parts (maxillæ and
lower lip or “tongue”), collect honey from many different kinds of
flowers. Body somewhat unwieldy, usually hairy. The fore wings are not,
as in wasps, folded together longitudinally when in a state of rest.
Eyes round. The legless, almost maggot-like larvæ are fed with pollen or
with a mixture of pollen and honey.
Most bees are colonial, and in these we find, besides the reproductive
individuals, workers which prepare the nest. This is for the most part
made up of “cells,” in the construction of which the most various
substances are used according to the species, _e.g._ wax, sand grains,
chewed wood, fragments of leaf. In each nest there is at the same time
only _one_ queen, who lays her eggs in the cells; the larvæ are
therefore developed in these cells, other cells serve for the storage of
pollen or honey. In the non-colonial bees there are no workers; in a few
of these species (parasitic bees, cuckoo bees) the female lays her eggs
in the cells of other species, which, like foster parents, undertake the
care of the strange larvæ. These species are naturally devoid of the
apparatus for securing and carrying pollen. In several bees (honey bees,
humblebees) this end is attained by the much-broadened shanks and first,
very large foot-joints of the hind legs. Other bees (_Megachile_) carry
pollen on the under side of the abdomen.
Bees play a very important part in the pollination (fertilization) of
many cultivated plants.
The =Honey Bee= (_Apis mellifica_) cannot be spoken of here; reference
must be made to works on apiculture.
The =Humblebees= (_Bombus_) are tolerably large, stout, thick-set, and
hairy. They construct nests below the surface of the soil (often in
peaty places), made up of oval or irregular waxen cells the size of a
hazel-nut. They fly rapidly, always making a humming sound. Many species
are black, with yellow and white, or red transverse stripes.
Honey-producing flowers in which the corolla is so long that even the
proboscis of humblebees cannot reach the honey hidden at the bottom of
the flower, (tobacco, field and garden beans) are gnawed at their base
by the sharp mandibles of the bees, so that a hole is made in the calyx
and corolla through which the tongue can be put. In this way the ovary
is sometimes wounded, and the normal development of the fruit rendered
impossible. Perhaps a certain amount of damage, always however
inconsiderable, may thus be effected.
Family: =Vespidæ= (_Wasps_).
Mouth-parts as in bees. Also with stings. Slender, and either hairless
or only slightly hairy. Eyes kidney shaped. Fore wings folded together
longitudinally when at rest (Figs. 61 and 88).
A distinction is made between solitary and social wasps; the latter
possess males, females, and workers. Only the fertilized queens survive
the winter. In the spring each of these begins to construct a nest (Fig.
88). In the wasp’s nest each comb consists only of a single layer of
cells, the openings of which are turned downwards. In a single nest
several of these horizontally placed combs are usually found one over
another, and are connected together by means of vertical pillars. Some
nests are built in hollow trees, others in holes in the ground; others
hang freely from trees, in which case they are covered by several layers
of a papery substance. The combs and cells are also made of paper, to
prepare which the insect gnaws and crushes decaying wood, and especially
bark, with its mandibles, mixing the crushed material with saliva. In
this way a pulp is made which is used in the construction of the nest,
and dries into a kind of paper. The opening of the nest is in its under
side (Fig. 88).
[Illustration:
FIG. 88.—The Common Wasp (_Vespa vulgaris_) and its nest.
]
During spring and summer the queen, or “wasp-mother,” lays only eggs
from which workers are hatched, which undertake the work of
nest-construction and care of larvæ, so that the queen can devote
herself exclusively to the function of reproduction. Towards autumn
males, and females capable of being fertilized, are also hatched; these
last afterwards live over the winter in the fertilized condition.
During summer the larvæ are fed by the workers with finely chewed
insects or with honey. They do not, however, suck the honey from
flowers, but steal it from several species of bee, or else form it in
their stomachs from sugary materials drawn from sweet fruits.
Wasps are harmful or troublesome in three ways: (1) by gnawing the bark
of trees; (2) by feeding on sweet fruits; (3) by the painful stings
which they inflict. These are most dangerous in hot summer days. If a
nest situated in the soil is destroyed during ploughing the alarmed
insects attack both men and horses, cases being known where their stings
have proved fatal. The pain is chiefly caused by the poison introduced
into the wound. On this account if the sting remains sticking in the
skin it must not be drawn out simply with the fingers, but carefully, by
means of the nails, lest the poison-bag is pressed and thus still more
poison brought into the wound. _Remedies_: Cooling substances, _e.g._
ground carrots, apples or pears, cabbage leaves, damp sand. Rubbing in
ammonia. If there is acute inflammation, a compress with sugar of lead.
Family: =Fossores= (_Digging Wasps_).
Several species of this group resemble the wasps in their habits, as
well as through their black and yellow-tinged abdomens; but they are
always distinguished from these by their fore wings, which are not
folded together in a state of rest, and by their eyes, which are not
kidney shaped. The shanks and feet possess thorns serviceable for
digging. The sting of the female has no barbs, so that it is not torn
off and left behind in the wound. The digging wasps are not social. They
are lively and active; in summer the female often flies busily about
near the ground in order to find a place for bringing up her young. She
digs a hole in the earth in which she lays an egg. Then she buries an
insect to serve as food for the young when hatched. Lest the insect to
be buried should decompose, while, on the other hand, a living animal
would not allow itself to be buried, the wasp first brings the insect
into a condition in which it cannot make any voluntary movements. For
this purpose most species sting the captured prey several times in the
body, and thus often injure the ventral ganglia (p. 84); by this
treatment the insect is not killed, but reduced to a condition of
apparent death. Most digging wasps are useful, since they chiefly bury
destructive kinds of insects. The =Common Sand Wasp= (_Ammophila
sabulosa_, Fig. 89), buries caterpillars; the =Path Wasp= (_Pompilius
viaticus_), spiders; the =Weevil-killing Sand Wasp= (_Cerceris
arenaria_) and the =Fly-killing Sand Wasp= (_Mellinus arvensis_)
respectively bury weevils and flies.
[Illustration:
FIG. 89.—The Common Sand Wasp (_Ammophila sabulosa_); natural size.
]
Family: =Formicidæ= (_Ants_).
Large strong mandibles adapted for biting; maxillæ and lower lip not
prolonged like a proboscis. Workers wingless; the males and reproductive
females have weakly veined wings. In correspondence with these facts,
the mesothorax which bears the larger wings is most strongly developed
in the last, but the prothorax in the workers. Abdomen united with the
thorax by a one- (_Formica_) or two-jointed (_Myrmica_) stalk. All
female ants, and naturally workers too, possess poison-glands, the
secretion of which accumulates in a poison-bladder; but the sting is
lacking in all species of _Formica_. The stingless ants (_e.g._ the Red
Wood Ant, _F. rufa_) inflict a wound with their strong mandibles, and
then, bending the abdomen forwards under the thorax, squirt the contents
of the poison-bladder into the wound. Ants form colonies, always of
large size, and consisting of reproductive and sterile individuals.
Their food is both of animal and vegetable nature, but chiefly consists
of insects and similar small animals. They mostly devour caterpillars,
but also dead or wounded beetles (_e.g._ cockchafers), mammals, birds,
and reptiles. As destroyers of caterpillars they are of use, but this is
true more of those living in woods than those which inhabit fields and
meadows. Ants are fond of all sweet substances; when they enter houses
the sugar jar is very often the end they have in view. They are
particularly fond of licking up the sweet juice which aphides excrete
from their abdomens. On plants infested with aphides many ants are found
which greedily sip up all the drops hanging from the abdomens of the
aphides; they may even promote the shedding of the juice by stroking the
abdomens of the little animals with their antennæ. There are, indeed,
species of ants which carry the aphides to the plant parts on which they
thrive best, and again, when these are sucked dry, transport them to
other uninjured parts. Sometimes aphides are kept in the overground or
underground nests of the ants. The common yellow meadow ants shelter
aphides in their subterranean nests, where they live on the roots of
grasses and other plants. In order to get, when necessary, fresh food
for these “milch kine,” they occasionally enlarge the nest, so that new
plant roots are laid bare, and they then carry the aphides to these.
During the greater part of the year only workers, larvæ, and pupæ are
found in an ants’ nest, but reproductive individuals appear in summer,
disappearing again before the cold weather comes on. As soon as there is
a sunshiny day they fly out, usually in large numbers. After pairing,
the females let themselves fall to the ground; they then either tear off
their own wings or this is done for them by the workers, which search
them out and take them to the nest, where the laying of eggs quickly
begins. The legless larvæ have feebly developed mouth-parts, and are fed
by the workers on food broken down by them. The pupæ vary; in the
sting-bearing ants (_Myrmica_) they are naked, in the stingless ants
(_Formica_), on the other hand, they are invested in a cocoon. The
latter kind of pupæ, known by the incorrect name of “ants’ eggs,” are
collected and used as food for insect-eating birds. The nests are made
either out of pine-needles and small branches heaped together (=Red Wood
Ant= = _Formica rufa_), or they eat out passages and cell-like spaces in
sound tree trunks (the larger =Wood Ants=, e.g. _F. herculeana_ and _F.
ligniperda_) or in decayed tree trunks (=Small Wood Ant= = _F.
fuliginosa_); others (=Yellow Wood Ants= = _F. flava_, etc.) make
passages and cavities in the ground, throwing up the earth into
ant-hills. _Damage_: Several species do harm by excavating the soil,
either in meadows and cornfields, by which the plants are killed and
harvesting rendered difficult, or under summer-houses and
dwelling-rooms. Others destroy tree stems. They are indirectly harmful
on account of the way in which they care for aphides, causing these
pests to increase to a greater extent than would otherwise be the case.
_Remedies_: If ants have got into a room the nest must be found if
possible, and the insects there destroyed with paraffin or boiling
water. If it proves to be too difficult to find and destroy the nest,
all the openings by which the ants can enter must be stopped up with
lime to which some extract of colocynth has been added. The nests found
in fields and gardens may sometimes be destroyed by quickly digging them
up, pouring paraffin over them, and then igniting it. It is also a good
plan to frequently tread or roll down the ant-hills which are thrown up,
as in this way they will be dispersed in the end. Ants are of service in
forestry, but scarcely in agriculture.
Family: =Ichneumonidæ= (_Ichneumon Flies_).
The species of ichneumon flies deviate in many ways from one another,
but they all have similar habits and play a similar part in nature. They
all have a longer or shorter ovipositor, always surrounded by two flaps,
and serving for laying eggs in other animals. Those which seek their
prey in branches and leaves generally possess a very short ovipositor
not obvious on cursory examination; those which lay their eggs in
insects inhabiting crevices, _e.g._ wood insects, are often provided
with a very long ovipositor. No colonies and, consequently, no workers.
The female ichneumon fly generally lays her eggs in the body of an
insect larva, on which the ichneumon larvæ developed from these eggs
feed, using up the reserve matter stored up in the fat body (p. 92).
Caterpillars are most infested; then follow false caterpillars, and then
the larvæ of weevils and leaf beetles. The eggs of a few kinds are laid
in pupæ, or even in the eggs of moths and butterflies. They always
select for this purpose those insects which possess reserve material.
The large kinds of ichneumon fly lay only a single egg in one host,
especially if the latter is not of large size; many of the smaller
ichneumons, on the other hand, lay many eggs (Fig. 90) in one host, even
up to a hundred or more. A caterpillar containing ichneumon eggs does
not at first appear different from other caterpillars, except that a
dark spot or patch usually indicates where its body was pierced by the
ovipositor of the ichneumon fly. The parasite breathes while in the host
by bringing the tip of its abdomen (where the main stem of the air-tube
system opens) into connection with one of the host’s spiracles. Since
the larva feeds altogether upon perfectly digestible substances an anus
is superfluous and is absent. Many ichneumon larvæ are ready to become
pupæ when the host is about to pass into the same condition; the larva
then bores through the skin of the latter, which quickly dies. Other
species do not attack the organs of the host so soon, but allow it to
become a pupa in peace, and then themselves become pupæ inside it; later
on, one or several ichneumon flies come out of this pupa instead of a
moth or butterfly. It is obvious that ichneumon flies are very
serviceable by destroying a large number of harmful insects. They
cannot, indeed, prevent the increase of any particular noxious insect,
but, when this takes place, they themselves increase to a greater
extent, and finally appear in such numbers as to make an end of the
pest.
[Illustration:
FIG. 90.—The Yellow-legged Ichneumon Fly (_Microgaster glomeratus_) of
the Cabbage Caterpillar. Left, the adult insect; right, the larva
(both enlarged). In the middle, Cabbage Caterpillar and a heap of
Microgaster pupæ.
]
I shall not enumerate here all the various ichneumon flies which benefit
agriculture, but simply mention the =Small Cabbage Caterpillar Ichneumon
Fly= (_Microgaster glomeratus_), depicted in Fig. 90, which, like its
host (the large cabbage white), appears in two generations. The larvæ of
the ichneumon fly live in large numbers in the large cabbage
caterpillar, and at their last moult acquire minute teeth, with which
they bite through the skin of their host; they then leave it to die, and
surround themselves with a cocoon close to its dead body. There are,
besides, a few small and also some large ichneumon flies which lay their
eggs in the pupæ of the cabbage white, so that, _e.g._, in winter many
of its angular pupæ, occurring on tree stems and hedges, are found with
many small or several large white ichneumon larvæ within them.
Family: =Tenthredinidæ= (_Saw_-_flies_).
Body thick-set. Abdomen never very long, and united by a broad base to
the thorax (Fig. 91). Saw-shaped ovipositor (p. 89), drawn in when not
in use, and only protruded during egg-laying. Mandibles strong, the
remaining mouth-parts not so well developed. The larvæ are false
caterpillars (p. 92); they can usually be recognized by their
characteristic attitude, for many of them bend the abdomen very much
upwards and forwards, especially when frightened, and when at rest the
hinder part of the body is spirally coiled (Fig. 91). The fully
developed larva spins a cocoon in which it still remains for a long time
in the larval condition, even during the whole winter. It becomes a pupa
two or three weeks before the appearance of the perfect insect. There
are many larvæ of this kind destructive to woods, but only a few which
interest the farmer. Here is included—
The =Turnip Saw-fly= (_Athalia spinarum_).
_Adult_: Female one-third of an inch long, stretch of wing over
two-thirds of an inch; male somewhat smaller. Bright orange or reddish
yellow. Head black, thorax and legs with black markings. Wings large.
_Larva_: Length may be rather more than two-thirds of an inch. The
just-hatched larvæ are almost colourless, but the skin quickly becomes
bright green, and after the first moult, dark green to black. Ventral
side slate grey. Head shining black. Twelve broad body segments, upon
which are many wrinkles of the skin.
[Illustration:
FIG. 91.—The Turnip Saw-fly (_Athalia spinarum_): adult female and two
caterpillars.
]
The sluggish adult is found, during May or August, upon kohl rabi and
turnips, mustard and charlock, with its wings folded together. The
female, by means of her ovipositor, saws small holes in the margin or
under side of the leaf, and lays her eggs in these. The larvæ are
hatched in from four to six days, and they undergo four moults. The
presence of the larvæ can be detected by their cast skins, which remain
sticking to the leaves even when the animals themselves, which are often
found rolled up on the under sides of the leaves, cannot be seen. The
enemy is also known by its way of feeding, for the larvæ keep on the
surfaces of the leaves (upper or under surface) and eat out longish
holes. As soon as these have reached a certain size, other parts of the
leaves or other leaves are attacked. When the larvæ are numerous the
holes continually increase in number until only the leaf-ribs are left.
The mature larvæ creep into the soil to a depth of from two-fifths to
four-fifths of an inch, and spin a small cocoon. The saw-fly emerges
either the same or the following year. These insects may therefore
appear in May or in August, but in many cases they are seen at only one
of these times, either the summer or autumn turnips being attacked, as
the case may be. _Remedies_: Fowls and ducks willingly eat the larvæ,
and, provided they are not able to do any damage, can therefore be
brought into the fields. Strewing with soot has a good effect. It pays
to pick off the larvæ from young plants.
ORDER 5: =Lepidoptera= (BUTTERFLIES AND MOTHS).
[Illustration:
FIG. 92.—Head of a Butterfly. A, eye; _Fh_, antennæ; Z, proboscis.
]
[Illustration:
FIG. 93.—Scales from a Butterfly’s Wing (strongly magnified).
]
Sucking mouth-parts, forming a “proboscis” made up of the two very long
maxillæ, spirally rolled up under the head when not in use (Fig. 92),
and adapted for sucking honey. There are some forms which take no food
in the adult condition, and in which the proboscis is short; in a few
species of hawk-moths, this organ is even longer than the body. The
larvæ (“caterpillars”) have biting mouth-parts. The body of a butterfly
or moth is covered with hair-like structures developed by the skin; in
the wings these are broader, have a characteristic appearance (Fig. 93),
and partially overlap one another. These scales cause the colours of the
wing. They can easily be wiped off, leaving the corresponding part of
the wing transparent and clear as glass. In many species (all
hawk-moths, many owlet moths) there is a _wing-hooklet_, i.e. the hind
wing has a spine or a thick brush which grasps a band-like area of the
fore wing. In this way the two pairs of wings are held together. The
females of a few species of spinner and looper moths are wingless, or
only possess short flap-like wings useless for flight. The metamorphosis
is complete (p. 89); the larvæ are true caterpillars; the pupæ are
obtectate (p. 93). Many caterpillars creep into the ground to become
pupæ, and spin no investment at all (_e.g._ hawk-moths). Others make a
cocoon, which may consist of threads loosely woven together or may be of
firm texture (Fig. 60). The cocoon consists chiefly of silk, a substance
secreted in a spinning gland, and exuding to the exterior on the lower
lip; but minute particles of sand or earth, and fragments of wood gnawed
off by the caterpillar, may be stuck in the cocoon. The pupæ of
butterflies are naked, without cocoon, but are fixed by threads to
leaves, tree stems, walls, hedges, etc. A distinction is drawn between
girdled and suspended pupæ; the first are fixed by a silk band, which
surrounds them, and the head is directed upwards, while the latter are
suspended by the tip of the abdomen (Fig. 94). The time required for the
development of the perfect insect from the pupa is not always the same,
depending not only upon the species, but also upon the time of year. The
summer generation of the large white spends scarcely fourteen days in
the pupa stage, the winter generation eight months.
Family: =Diurna= (_Butterflies_).
Body relatively weak and thin; wings very broad, not very long
relatively. No wing-hooklet (_see above_). Wings folded together above
in a state of rest, so that their upper sides touch. Antennæ thickened
in a club-like way at the tip. The caterpillars possess five pairs of
pro-legs; they are usually almost devoid of hair. There are, however, a
few (_e.g._ the caterpillar of the peacock butterfly, Fig. 94) which
possess hard, spine-like, much-branched bristles. The naked pupæ are
sharp cornered; some are girdled, others suspended (p. 137).
[Illustration:
FIG. 94.—The Peacock Butterfly (_Vanessa io_), with pupa, and larva
suspended before passing into the pupa state.
]
Among butterflies with larvæ that become suspended pupæ are the =Red
Admiral= (_Vanessa atalanta_), the =Peacock= (_Vanessa io_, Fig. 94),
the =Fritillaries= (_Argynnis_), the =Meadow Browns= (_Hipparchia_),
etc.; and among those with girdled pupæ the =Swallow Tail= (_Papilio
machaon_), the =Whites= (_Pieris_), etc.
The =Cabbage White=, or =Large White= (_Pieris Brassicæ_).
_Butterfly_: Length a little over an inch, span of wing 2½ inches. Both
fore and hind wings milky white, the former black at the root, on the
front edge, and the outer angle; also a black patch on the inner margin
of the fore wing, passing on to the front margin of the hind wing. The
female possesses, in addition, two round black patches on the middle of
each fore wing. Under side of the fore wings milky white, yellow at the
tip, blackish at the root; under side of the hind wings yellow, with
black dots. _Caterpillar_ (Fig. 95): As much as 1⅓ inch long; greenish,
or sulphur yellow, with black dots. Head and dorsal side of last segment
of the body grey with black spots. Young specimens are of a very bright
green with black wartlets closely crowded together.
[Illustration:
FIG. 95.—The Cabbage White (_Pieris brassicæ_) female laying her eggs;
caterpillar, and pupa.
]
From the pupæ which have lived through the winter butterflies emerge in
May, and lay their golden yellow eggs in small heaps on the under sides
of the leaves of rape, mustard, and cress, also on charlock and
such-like cruciferous weeds. The caterpillars of this first generation
are hatched in fourteen days, and rarely do any harm, since they only
appear in small numbers. They develop rapidly, and during the last days
of June become pupæ on the branches and leaves of the plants they live
on; the butterflies appear in July. Owing to their rapid development the
caterpillars and pupæ of this first generation are but little exposed to
the attacks of enemies (ichneumons, birds, etc.). Only a few of them
die, therefore, if the weather is favourable. As a result of this, the
July butterflies and the eggs laid by them are relatively numerous, so
that the number of caterpillars appearing in late summer may be very
large. These caterpillars, however, live almost exclusively on the
various kinds of cabbage and kohl rabi, and it is this second generation
which in many years is so harmful. At the beginning of August the
caterpillars are ready to become pupæ, and for this purpose they seek
tree stems, hedges, walls, etc. The pupæ now formed live as such through
the winter. During this period, however, they are exposed to many
dangers (damp, cold, sudden alternation between very low and very high
temperatures; ichneumons, birds), and most of them perish, so that only
a few butterflies come out the following spring, and lay but a few eggs.
It is therefore obvious that the first generation of caterpillars (May,
June) is much less numerous than the second generation occurring from
late summer to autumn. Under exceptionally favourable conditions even a
third generation may appear, since caterpillars of the second generation
are able to become pupæ at the beginning of August; and these pupæ,
instead of remaining as such over winter, become butterflies the same
month. These, again, lay eggs from which the caterpillars of the third
generation are hatched, which, however, are not always fully developed
before the advent of the cold weather, and in this case perish. It is
clear that, in the case of pupæ which develop into butterflies during
August in about fourteen days, the unfavourable influences have either
no effect (unfavourable weather) or but little (ichneumons, birds), so
that the butterflies appear in flocks, which wander into other regions,
since they have themselves, when larvæ, devoured the cabbage and turnip
plants. In reference to the damage effected by the caterpillar, it may
be observed that only the chief veins of the leaf are left, and the
margins are not spared. _Remedies_: Collection of the little heaps of
yellow eggs and the young caterpillars, which are blackish and live
together in small companies; the planting of a few small hemp plants in
the cabbage fields to be protected, by which the butterflies will be
kept away.
The =Garden White=, or =Small White= (_Pieris rapæ_).
[Illustration:
FIG. 96.—The Garden White (_Pieris rapæ_), male.
]
[Illustration:
FIG. 97.—The Garden White (_Pieris rapæ_), female, caterpillar.
]
_Butterfly_ (Figs. 96 and 97): Length rather less than an inch, span of
wing two inches; very much like the cabbage white. Base and tip of the
fore wing not of such a deep black colour; the black patch in the inner
margin of the fore wing is usually absent in the female. The male,
however, very often has a black patch in the upper side of the fore
wing. _Caterpillar_: Just over an inch long. Dull green; a longitudinal
yellow line on the back; also the black stigmata are connected by a
yellow line. Habits as in the preceding species; the female, however,
lays her yellow eggs separately, and not in heaps, and the second
generation of caterpillars usually become pupæ somewhat later in the
year. Collecting is more difficult than in the preceding species, since
the young caterpillars live independently, and their colour makes it
difficult to recognize them on the green cabbage leaves.
The =Green-veined White= (_Pieris napi_).
_Butterfly_ (Fig. 98): As large or somewhat smaller than the preceding
species. Wings milky white on their upper side; fore wings dusted with
black on their front margin, tips, and ends of the ribs. Two spots on
the middle of the fore wing in the female, one or none in the male.
Under side of the hind wings yellow; under side of the veins dusted with
greenish grey. _Caterpillar_: A little over an inch. Dull bluish-green,
with minute blackish tubercles above, and whitish ones below. A yellow
longitudinal line on each side connecting the black spiracles, which are
bordered by reddish yellow. Very like the preceding species in the
larval condition. Habits as in the preceding species, but this is less
common.
[Illustration:
FIG. 98.—The Green-veined White (_Pieris napi_).
]
Family: =Noctuidæ= (_Owlet Moths_).
Night-flying moths, of medium size and dull colour, with smooth-haired
bodies. Antennæ long and thin, thread like,—comb-shaped only in the
males of a few species; wings powerful, lie in a roof-like way when at
rest; almost always a wing-hooklet. Caterpillars usually hairless;
mostly with five pairs of pro-legs, a few with four or three pairs. The
owlets pair at night; they also fly about during the day, even in bright
sunshine. Flight strong and rapid, but always in fits and starts. Almost
all species lay their eggs separately, and on herbs, only a few species
on trees. The caterpillars are very much scattered, and the damage
caused by them is never great, except in spots here and there,—on the
contrary, when they increase to a great extent they spread over a wider
area. Several species are harmful to agriculture.