Guide to the study of insects, and a treatise on those injurious and beneficial to crops: for the use of colleges, farm-schools, and agriculturists online

tergitc (/). (a, eye; /*, lingua; o, ovipositor, two outer
rhabdites exposed to view.) The abdominal spiracles in Figs.
65 and f>(5, are represented by a row of dots. In the pupa
they are concealed by the tergites, which overlap the sternites.

Fig. 67 represents the pupa state, where the body has become
much shorter, and the appendages of the head and thorax greatly
differentiated ; the external genital organs are wholly retracted
within the cavity of the abdomen ; the head is freer from the
body, and the whole bulk of the head and thorax together, in-
cluding the appendages, greater than that of the abdomen.
These changes of form, assumed by the insect in its passage
from the larva to the pupa state, are nearly as striking as
the so-called "hypermetainorphosis" of Meloe and Sitaris
described by Newport and Fabre. (/, mesoscutellum ; p, cly-
peus ; g, maxilla; with the palpi ; r, lingua.)

We have also observed similar changes in the semi-pupa of a
Tineid larva, which we found in the mud-cells of Odynerus
cdbo2)halemtus. There were over a dozen specimens in different
stages of growth from the larva to the pupa, which were but
partially panily/ed by the well-directed sting of the intelligent
wasp, so that some continued to transform into perfect pupae.

The following changes were noticed: the larva straightened
out, and became a little shorter, the prothoracic ring remaining
the same ; the head of the pupa being beneath it ; the meso-



68 THE CLASS OF INSECTS.

thoracic ring enlarged, swelling and rounding above and on the
sides, and with this increase in size drawing the meta-thorax
forwards. The first visible portion of the pupa beneath is the
mesothorax. The thoracic legs of the larva are now con-
stricted at their base, and have become useless.

In the next stage, the most important change noticed is in
the metathorax, which now becomes broadly heart-shaped. In
a succeeding stage, the whole thorax bulges out, and is much
larger and clearly distinguished from the head and abdomen.
The prothorax of the larva disappears, and that of the pupa
takes its place. The occiput of the pupa, just before the larva-
skin is thrown off, can be distinctly seen under the larval occi-
put, pushing aside each half of the latter.

In the last stage of Bombus just before the imago leaves its
cell, the body and limbs are surrounded by a thin pellicle.
This pellicle also envelops the moth, just before it leaves the
pupal state, and is cast off when it moults the pupa-skin. This
is probably identical with the skin cast by the active subimago
of Ephemera, soon after it has taken its flight. Westwood also
considers this subimago skin identical with that covering the
bodies of coarctate Diptera, as in Eristalis.

Newport states, that when the imago of Sphinx is about to
cast off the pupa- skin the abdominal segments are elongated
beyond their original extent, this being the first part of the
insect that is entirely freed from its attachment within the
pupa-case. After this the thorax slits down, and the body is
drawn out of the rent. In the Butterfly the wings mature in a
few moments, but those of Sphinx being thicker, require two
or three hours.

Newport (Philosophical Transactions, London, 1832 and
1834) has detailed with great minuteness the internal changes
of Sphinx ligustri while transforming. The most marked
changes are in the nervous and digestive systems.

Several anomalous modes of metamorphosis have been ob-
served, one in Diptera and the other in Sitaris and Meloe. The
development of the latter insect will be noticed beyond.

Sir John Lubbock has described the singular metamorphosis
of Lonchoptera, which he considers to be allied to Sargus,
though the adult stages differ greatly. The larvae are oblong



TRANSFORMATIONS OF THE INSECT. 69

ovate, flattened, with four long setae in front and two behind,
with the sides of the body emarginate and spinulated. They
were found under logs. " When the larva is full grown, it de-
taches itself from the skin, which retains its form, and within
which the insect changes into a white opaque fleshy grub con-
sisting apparently of thirteen segments which gradually dimin-
ish in size from one end to the other. There are no limb-cases.
According to analogy the pupa should be ' incomplete ; ' it is
probable, therefore, that the legs and wings make their appear-
ance at a later stage. If this be so the perfect form is only
attained after passing through three well-marked stages. I re-
gret, however, that the specimens at my disposal did not enable
me to decide this point." (Trans. Ent. Soc. London, Third
Ser. i, 1862.)

Haliday states that Tlirips goes through a propupa and pupa
stage. There are five well-defined stages in the Homopterous
Typldocyba, and more than three in Aphis. Yersin has noticed
several stages in the development of Gryllus campestris, and
the genus Psocus has four such stages.

The duration of the different stages vary with the changes
of the seasons. Cold and damp weather retards the process of
transformation. Re'aumur kept the pupa of a Butterfly two
years in an ice-house before, on being removed to a warm place,
it changed to a butterfly. Chrysalids survive great alter-
nations of heat and cold ; they may be frozen stiff on ice, and
then, on being gradually exposed to the heat, thaw out and
finish their transformations.

Retrograde Development. There are certain degradational
forms among the lowest members of each group of Insects
which imitate the group beneath them. The Tardigrades (which
are considered by some authors to be allied to the Mites) are
mimicked by the low parasitic worm-like Demodex folliculorum ;
the low Neuroptera, such as Lepisma, imitate the Myriapoda ;
and the wingless Lice remind us of the larvae of the Neuropter-
ous Hemerobius.

Among the Coleoptera, the history of Stylops affords a strik-
ing example. The active six-footed larva is transformed into
the strange bag-like female which takes on the form of a cylin-
drical sac, the head and thorax being consolidated into a



70 THE CLASS OF INSECTS.

minute flattened portion. The process of degradation here
seems carried out to its farthest limit.

Thus the degraded forms of the lower series of Hexapods
take on a Myriapod aspect. In the more highly cephalized
Diptera, Lepidoptera, and Hymenoptera the degraded forms
are modelled on a higher articulate type. The idea of a divis-
ion into three regions is involved. Thus the wingless forms
of Flies, such as the Bird-louse, Nirmus; the Bat-tick, Nycte-
ribia; the Bee-louse, Braula; and Chionea resemble strikingly
the biregional Arachnids.

In the wingless female of Orgyia and the Canker-worm moth,
the head is free, but the thorax is merged into the abdomen.
The resemblance to the lower insects is less striking. The
worker ants and wingless Ichneumons, Pezomachus, still more
strictly adhere to the type of their suborder, and in them the
triregional form of the body persists. Among the first of the
examples here cited we have seen the workings of a law, by
which most degraded forms of insects (and this law is exerted
with greater force in Crustacea) tend to revert to the worm-like,
or, as we may call it, the archetypal, form of all Articulata.

We have seen that many winged forms mimic the groups
above them, whereas the wingless degraded species revert to a
worm-like form. In either case, the progress is towards a
higher or a lower form. The latter is the more exceptional, as
the evolution and growth of all animals is upwards towards a
more specialized, differentiated form.

The Imago. After completing its transformations the adult
insect immediately seeks to provide for the propagation and
continuance of the species. The sexes meet, and, soon after,
the male, now no longer of use in the insect economy, perishes.
The female hastens to lay her eggs either in, upon, or near
what is to be the food of the young, and then dies. This
period generally occurs in the summer and autumn, and during
the winter the species is mostly represented by the egg alone.
Rarely does the adult insect hibernate, but in many species
the pupa hibernates to disclose the adult in early summer.
The larva seldom, as such, lives through the winter.

Re'aumur kept a virgin butterfly for two years in his hot-
house. From this it would seem that the duration of the life



GEOGRAPHICAL DISTRIBUTION. 71

of an insect may be in this way greatly prolonged. Most in-
sects live one year. Hatching from the egg in early summer,
they pass through the larva state, and in the autumn become
pupa 1 , to appear as imagos for a few days or weeks in the
succeeding summer. Many Lepidoptera are double-brooded, and
some have even three broods, while the parasitic insects such as
Lice and Fleas, and many Flies, keep up a constant succession
of broods. Warmth, Mr. R. C. R. Jordan remarks in the Ento-
mologists' Monthly Magazine, has much to do with rapidity
of development, as insects may be forced artificially into hav-
ing a second brood during the same season. Some Coleoptera,
such as the Lamellicorns, are supposed to live three years in
the larva state, the whole time of life being four years. The
Cockchafer (Melolontha) of Europe is three years in arriving
at the perfect state, and the habits of the Goldsmith Beetle
(Cotalpa hiuiyent), according to Rev. Samuel Lockwood
(American Naturalist, vol. 2, p. 186), and of the June Beetle,
and allied genera, are probably the same.

GEOGRAPHICAL DISTRIBUTION. The insect-fauna of a coun-
try comprises all the insects found within its limits. The
Polar, Temperate, and Tropical zones each have their distinct
insect-fauna, and each continent is inhabited by a distinct
assemblage of insects. It is also a curious fact that the insect-
fauna of the east coast of America resembles, or has many an-
alogues in, that of the Eastern hemisphere, and the west coast
of one repeats the characteristics of the west coast of the
other. Thus some California insects are either the same spe-
cies or analogues (i.e. representative species) of European
ones, and the Atlantic coast affords forms of which the ana-
logues are found in Eastern Asia and in India. This is corre-
lated with the climatic features which are repeated on alternate
sides of the two hemispheres.

The limits of these faunae are determined by temperature and
natural boundaries, i. e. the ocean and mountain ranges. Thus
the insect-fauna of the polar regions is much the same in
Europe, Asia, and North America ; certain widely spread polar
species being common to all three of these continents.

When we ascend high mountains situated in the temperate



72 THE CLASS OF INSECTS.

zone, whose summits nearly reach the snow-line, we find a
few insects which are the same or very similar to those of the
polar regions ; such an assemblage is called an Alpine fauna.

The insect-fauna of each great continent may be divided into
an Arctic, or polar, a Temperate, and a Tropical fauna, and an
Alpine fauna if there are mountains in the warm latitudes which
reach near the snow-line. Mountain barriers, inland seas, des-
erts, and peculiarities in the flora (or collection of plants
peculiar to a certain district), are boundaries of secondary
importance in limiting the distribution of species.

On the other hand insects are diffused by winds, rivers,
oceanic currents, and the agency of man. By the latter im-
portant means certain insects become cosmopolitan. Certain
injurious insects become suddenly abundant in newly cultivated
tracts. The balance of nature seems to be disturbed, and
insects multiplying rapidly in newly settled portions of the
country, become terrible pests. In the course of time, how-
ever, they seem to decrease in numbers and moderate their
attacks.

Insect-faunae are not limited by arbitrary boundaries, but
fade into each other by insensible gradations corresponding in
a general way to the changes of the temperature of different
portions of the district they inhabit.

The subject of the geographical distribution of insects, of
which we have as yet but given the rudiments, may be studied
to great advantage in North America. The Arctic insect-fauna
comprises Greenland, the arctic American Archipelago, and the
northern shores of the continent beyond the limit of trees. A
large proportion of the insects found in this region occur in
arctic Europe and arctic Asia, and are hence called circum-
polar, while other species are indigenous to each country.
Again, the arctic fauna of Labrador and Hudson's Bay differs
from that of the arctic portions of the region about Behring's
Straits, certain species characterizing one side of the continent
being replaced by representative species which inhabit the
opposite side.

The Alpine fauna of the White Mountains consists, besides
a very few peculiar to them, of circumpolar species, which are
now only found in Labrador and Greenland, and which are



GEOGRAPHICAL DISTRIBUTION. 73

supposed to be relics of a glacial fauna which formerly inhib-
ited the northern pnrt of the temperate zone, and in former
times followed the retreat of a glacial, or arctic climate from
the low-lands to the Alpine summits. These patches, or out-
liers, of an Arctic fauna, containing however a preponderance
of subarctic forms, also occur in the colder parts of New
England.

The subarctic fauna is spread over British North America,
stretching north-westerly from the interior of Labrador and the
northern shores of the St. Lawrence, following the course of
the isothermal lines which run in that direction, and north of
which no cereals grow. There are subarctic forms which inhabit
the shores of the Bay of Fundy, especially about Eastport,
Maine, where the fogs and cold arctic marine currents lower
the climate.

Dr. J. L. Leconte, in a paper on the Coleoptera of Kansas
and Eastern New Mexico (Smithsonian Contributions to Knowl-
edge), thus subdivides the Coleopterous fauna of the United
States, and gives a useful map to which the reader is referred.

"The whole region of the United States is divided by merid-
ional, or nearly meridional lines into three, or perhaps four,
great zoological districts, distinguished each by numerous
peculiar genera and species, which, with but few exceptions, do
not extend into the contiguous districts. The eastern one
of these extends from the Atlantic Ocean to the arid prairies on
the west of Iowa, Missouri, and Arkansas, thus embracing
(for convenience merely) a narrow strip near the sea-coast of
Texas. This narrow strip, however, belongs more properly
to the eastern province of the tropical zoological district of
Mexico.

"The central district extends from the western limit of the
eastern district, perhaps to the mass of the Sierra Nevada of
California, including Kansas, Nebraska, Utah, New Mexico,
Arizona, and Texas. Except Arizona, the entomological fauna
of the portion of this district west of the Rocky Mountains,
and in fact that of the mountain region proper, is entirely un-
known ; and it is very probable that the region does in reality
constitute two districts bounded by the Rocky Mountains, and
the southern continuation thereof.



74 THE CLASS OF INSECTS.

"The western district is the maritime slope of the continent
to the Pacific, and thus includes California, Oregon, and Wash-
ington Territories.

"These great districts are divided into a number of prov-
inces, of unequal size, and which are limited by changes in
climate, and therefore sometimes distinctly, sometimes vaguely
defined."

"The method of distribution of species in the Atlantic and
Pacific districts, as already observed by me in various memoirs,
is entirely different. In the Atlantic district, a large number
of species are distributed over a large extent of country ; many
species are of rare occurrence, and in passing over a distance
of several hundred miles, but small variation will be found in
the species obtained. In the Pacific district, a small number
of species are confined to a small region of country ; most
species occur in considerable numbers, and in travelling even
one hundred miles, it is found that the most abundant species
are replaced by others, in many instances very similar to them ;
these small centres of distribution can be limited only after
careful collections have been made at a great number of locali-
ties, and it is to be hoped that this very interesting and im-
portant subject of investigation may soon receive proper atten-
tion from the lovers of science of our Pacific shores.

4 ' In the Central district, consisting, as it does to a very
large extent, of deserts, the distribution seems to be of a mod-
erate number of species over a large extent of country, with a
considerable admixture of local species ; such at least seems to
be the result of observations in Kansas, Upper Texas, and
Arizona."

There are a very few species which range from New England
to Brazil, and fewer still (Xyleutes robinice, according to Bois-
cluval, is found in California) range from New England to
California. Junonia ccenia, according to authors, is found both
in the Southern States and California, and Pyrrharctia Isabella
of the Eastern States would be easily confounded with P. Call-
fornica.

Variation. Islands afford more variable forms than conti-
nents ; the Madeiran insects and those of Great Britain vary
more than the same species found on the continent of Europe.



GEOGRAPHICAL DISTRIBUTION. 75

A species spread through two zones of temperature also varies ;
many European species, according to McLachlan, becoming
"inchinixcd" ill going northward, while others become paler.
Such varieties have been described as different species.

M r. Alfred Wallace finds that the most constant forms of
species are those the most limited in their geographical range
as to a particular island, while those species, which range over
a large part of the Malayan Archipelago, vary very consider-
ably. It is a general rule throughout the animal and vegetable
world, that the most widely spread species are those capable of
withstanding the greatest climatic changes, and adapting them-
selves to the greatest diversities of topography.

AVliile the most widely distributed species are thought to be
the most variable, Mr. Scudder finds in the genus Chionobas
that C. semidea, restricted to the summit of Mt. Washington
varies almost as much as C. Oeno, which is circumpolar, being
found both in Labrador and Northern Europe.

Mr. AVallace (Transactions of the Linmean Society, xxv,
1865, p. 14) mentions the following facts "as showing the
special influence of locality in giving a peculiar fades to the
several disconnected species that inhabit it."

"On examining the closely allied species, local forms, and
varieties distributed over the Indian and Malayan regions, I
find that larger or smaller districts, or even single islands, give
a special character to the majority of their Papilionidae. For
instance: 1. The species of the Indian region (Sumatra, Java,
and Borneo) are almost invariably smaller than the allied spe-
cies inhabiting the Celebes and Moluccas ; 2. The species of
New Guinea and Australia are also, though in a less degree,
smaller than the nearest species or varieties of the Moluccas ;
3. In the Moluccas themselves the species of Amboyna are larg-
est ; 4. The species of Celebes equal or even surpass in size those
of Amboyna; 5. The species and varieties of Celebes possess
a striking character in the form of the anterior wings, differing
from that of the allied species and varieties of all the surrounding
islands ; 6. Tailed species in India or the Indian region become
tailless as they spread eastward through the archipelago."

Variety breeding. Varieties may be produced artificially ;
thus negro varieties of insects may be raised "from parents



76 THE CLASS OF INSECTS.

more or less tainted with melanism, and according to Knaggs,
there is a "frequent recurrence of individuals wanting a hind
wing, which may be noticed even at large in Macaria notata."
"Few species are liable to the same extent of variation, and
many apparently to none at all." Certain species vary "ac-
cording as they may have reproduced, generation after gen-
eration, on a chalky, peaty, gravelly, or other soil." Food also
exerts an influence in inducing variation, according as cater-
pillars of the same species feed on different plants ; this occurs
most commonly in the Micro-lepidoptera. (Knaggs, in the
Entomologist's Monthly Magazine, London.)

Introduced species of insects, like those of plants, often thrive
more vigorously than the native forms. This is instanced by
native insects which abound in unusual numbers in newly
cleared districts where the former presence of forests and
their natural foes kept them under. The Potato-beetle, Can-
ker-worm, and Cliswcampa must have lived formerly in mod-
erate numbers on our native plants, where now countless hosts
affect our introduced plants. Among species introduced from
a foreign country we have only to instance the Hessian Fly,
the Wheat-midge, the Coddling-moth, the Clothes-moth, the
Apple Bark-louse, and the Grain-weevil. Mr. W. T. Brig-
ham informs us that some of the most abundant insects in the
Hawaiian Islands are introduced species carried by vessels
from Europe. Vanessa Antiopa, Pyrameis cardui, and P.
Atalanta, so abundant in this country, are supposed to be intro-
duced butterflies. Aphodius jimetarius, found by us living in
dung on Mt. Washington, is one of our most common beetles,
and the Asparagus-beetle, introduced from Europe a few years
since, is common in gardens in Eastern New York, while Mr.
Walsh has recorded the appearance of the European Gooseberry
Saw-Fly, which ravages the Gooseberry and Currant. Pieris
rapce, the Cabbage-butterfly, introduced from Europe into
Quebec about 1859, soon became abundant within a circle of
forty miles radius about that city, and has even spread into
Maine and Vermont along the railroads leading from Quebec.

Insect Years. There are insect years as well as "apple
years," seasons when insects most abound. Every collector
knows that there are certain years when a particular species of



GEOLOGICAL DISTRIBUTION. 77

insect is unusually common. The Army-worm, Leucania uni-
juinrfii, swarms in countless numbers in a summer following
a dry mid warm spring. After a cold and rainy spring, insects
aiv less abundant. Mr. F. Smith remarks that in England the
suinnuT and autumn of I860 were unusually wet, which dis-
abled the bees, wasps, and fossorial hymenoptera generally, in
building their nests. We know how ants are hindered from
building their nests by rain, and in a very rainy season num-
bers probably die. A succession of rainy seasons caused the
Andrenae, or Spring bees, to disappear from the vicinity of
London. While a severe winter, if the cold be continuous, is
not injurious to insects, mild periods in winter, when it is warm
enough to rouse them from torpidity, are as fatal to insects as
to vegetation, should severe cold immediately follow.

GEOLOGICAL DISTRIBUTION. The geological distribution of
insects corresponds generally with that of other animals,
though insect-remains are few in number, owing naturally to
the difficulty with which their fragile forms are preserved
in the rocks. Professor C. F. Hartt has discovered near St.
John, New Brunswick, the oldest insect-remains in the world.
They occur in some plant-beds of the Upper Devonian forma-
tion, and consist of six species of Neuroptera. Mr. Scudder,
who has referred to them in vol. 1 of the American Naturalist,
states that with the exception of one or two Ephemeridte, or
May-flies, they mostly represent families which are now extinct.
He describes a gigantic May-fly, Platepliemera antiqua (PL 1,
fig. 3) ; Lithentomum Harttii (PL 1, fig. 5) ; Homothetus fossi-
lis (PL l,fig. 7) ; and Xenoneura antiquorum which is supposed
to bear a stridulating organ like that of the Grasshoppers,
so that he "is inclined to believe there were chirping Neu-
roptera in those days."

Ascending to the Carboniferous rocks, insect-remains appear
more abundant. At Morris, Illinois, have been collected some
remarkable forms. Among them are Miamia Bronsonii Dana
(PL 1, fig. 1), allied to the White Ants arid Hemeristia occi-
dentalis Dana, allied to Hemerobius and Cln-ysopa; with these
occurred remains at first supposed by Prof. Meek to be those
of a caterpillar (Fig. (>8), but now thought to belong to
some worm.




78 THE CLASS OF INSECTS.

In the Coal-beds of New Brunswick and Nova Scotia, Dr.
Dawson, Mr. Barnes, and Professor O. C. Marsh have discovered