PREPARATION FOR A CHANGE.
The last stage of the larva's history hastens on. Its career of
activity and voracity is nearly ended, and the insect's days in this
form are well nigh spent. Hitherto it has been an earthly, earth-loving
being, without either the desire or the power to raise itself into
the airy element, in which multitudes of its species are disporting
the day long. If we may so speak, its highest desires have only been
confined to the quality and quantity of its food; possessing these, it
was content. But now, its hours of feasting are come to a close, and it
has to make ready for a great and momentous change. The crawling, and,
perhaps, repulsive creature which we turn from without regret, has a
high destiny to accomplish, when the period of its sojourn in its vile
body is fully accomplished; and then, that form which now creeps among
the dust of the world, shall mount up as on eagles' wings, and be
carried whither it will through the pure regions of the sky.
The age to which the larva generally attains before this change takes
place is exceedingly variable. To some it is permitted to reach the
venerable age of four or five years; others, three; and many, not
nearly so much. The dung and fungus-feeding insects, as if hastened
forward by the warmth of their position, are at the end of their larva
life in a week; others live a fortnight in this state; and others,
several months. We are told of a curious anecdote of a beetle which had
existed in a desk, set up in an office in London, for upwards of twenty
years, half of which period, according to Messrs. Kirby and Spence,
it must have lived as a larva. But this is quite an exception to the
general rule.
For some days before, the larva loses its long distinguishing
characteristic--its appetite--and now forsakes the plants upon which
it formerly fed; or if it does not forsake them, no longer consumes
any part of them. It becomes, apparently, in some degree sensible
that it is approaching the most dangerous period of the history of
the insect--the state of sleep or torpor in which it is to exist as a
pupa--of which we shall speak more particularly in our next chapter.
Before, although a weak and comparatively a defenceless creature, it
was still able to exercise a vigilant watch against its enemies, and
thus to avoid them, or to prepare for their reception; but now, its
eyes are to be closed in a death-like slumber; its body to hang a
tempting bait to any wandering foe, or hungry bird, and it can in no
way resist the attacks of the feeblest adversary.
As if fully aware of this, the wonderful instinct of the larva meets
the difficulty by teaching it to select the best place for its
concealment from a dangerous notice. With this view, it sets out in
search of a hiding-place, and rests not until it has obtained a city
of refuge which may prove to it a defence against the enemy. It may be
some little recess, covered by an irregular stone, and sheltered round
the sides by moss and the upspringing grass; or, perhaps, a little hole
in the earth has received the poor fugitive from future harm, and in
order to conceal itself more completely, it has drawn over the mouth
of the cave a covering of leaves. Here, safe from observation, the
larva bids a farewell--to speak as the poets speak--to the busy staring
world for awhile, and loses all recollection of its past history, in
the night of torpidity upon which it has now entered. The larvæ of the
lady-bird, and other insects, glue themselves fast to the under side of
a twig or leaf, and here pass the days of their sleep in safety. Many
of the larvæ of insects whose life, up to this period, has been passed
beneath the surface of some glassy pool, now quit the pure element,
and seek the shore, on which they are to pass the remaining portion of
their existence.
But there are two other ways in which larvæ prepare for the state
of _pupa_, which are so curious, and prevail to such a large extent
among insects, that we may be excused for following the example of
all authors upon insect history, and treating our readers to the
interesting facts which have been recorded by various observers upon
this subject. One of these is the plan of hanging themselves up in
the air, like sailors in their hammocks; and in other positions, this
plan is commonly called the _suspension_ of the larva. The other is
the formation of beautiful cases of various kinds, which are called
_cocoons_, in which they wrap themselves up close during the period to
be devoted to the pupa state. Let us speak of these each separately;
and, first, of the case, or _cocoon_, as a place of concealment for the
larva. It is right, however, to premise, that, while the greater number
of insects are in a torpid or half-torpid state while in the pupa form,
all are not so, as will be noticed in the next chapter; and those which
are not do not of course require the protection of a cocoon, or the
contrivance of a silken hammock.
The material of which the case or cocoon is composed is a beautiful
silken fibre, which is furnished by a spinning apparatus placed either
at the extremity of the body, or more frequently at the mouth of
the insect, whence it proceeds in a filament of the utmost delicacy
and transparency, but at the same time of considerable tenacity. By
its means alone cocoons, of a number of different kinds, some of
extraordinary beauty and ingenuity, are constructed; but in other
cases the insect has recourse to various materials to assist in giving
strength to the walls of its cell.
[Illustration: _Cocoon of Silk-worm._]
The best example, and the most familiar one we can select of a purely
silken cocoon, is that of those
"----spinning worms
That in their green shops weave the smooth-haired silk."
This beautiful and valuable cocoon, when examined externally, appears
to be formed in two different ways; for the outer covering is loose and
open, while the inner one is compact and close, and so in truth it is,
although both coverings are formed of a single thread. The outer has
been called the _scaffolding_, by means of which the inner and more
solid covering is constructed. The larva stationing itself between two
leaves, or in any other suitable spot, fastens its thread to one of the
adjoining surfaces, and then proceeds to draw out the fibre and fasten
it in various positions until it has woven around itself an envelope,
as it were, of loose gauze. After this has been done it begins to form
the closer and more compact structure of the inner envelope, laying
on the silk backwards and forwards in a series of zig-zags, until it
has laid on several layers, and thus completely shut itself in. The
loose outer portion forms what ladies so well know under the title of
flos-silk; the inner fibres are the most continuous, admitting of being
wound off without breaking, and they form the ordinary silk of commerce.
[Illustration: _The Larva surrounded by its Palisade._]
M. Lyonnet has given a most interesting account of the proceedings of
another larva which far surpasses the silk-worm in the ingenuity of its
manner of forming the cocoon. This larva is very small; in fact, not
more than the sixth of an inch in length, and is found on the under
side of oak-leaves. M. Lyonnet observes, that beyond all the larvæ he
had ever watched, he considered this creature the most inconceivably
ingenious workman. Its little cocoon is of a white colour, and of a
long oval form, having its upper surface ornamented with seven upright
ridges. The first thing the creature begins by doing, is to erect,
in the most curious manner, a series of little upright palisades of
silk at a certain distance from each other, all round its body, so
as to form a sort of oval fence, and probably the larva intends them
to serve as a sort of hedge to keep off intruders while it is busy
at work! After spinning half its case, it turns round, and begins at
the opposite end, and thus forms the other half; it then unites it
in the middle, and by so doing incloses itself in a very pretty cage
of silken net-work, which it subsequently strengthens by adding a
firm layer on the inside. The time taken in the construction of this
ingenious cocoon is not more than half-an-hour. It is quite impossible
to understand how the little being contrives to form the upright ridges
on the surface of its cocoon; and as the larva is so minute it is
almost hopeless to expect to discover it. Attempts have been made to
unravel the difficulty, but not with complete success. When, looking at
some magnificent works of man, we are tempted to become inflated with
pride, let the remembrance of what this tiny insect can do keep us
humble, and direct our admiration rather to Him who is the Author of
all wisdom, the Giver of every good and perfect gift.
Upon the leaves of pear trees we may sometimes find a pretty cocoon of
very slight and elegant texture, formed of silk, as shown in the cut.
[Illustration: _Cocoon on a Pear-leaf._]
A very singular cocoon is spun by the larva of a common moth, somewhat
of the outline of a balloon in form. This cocoon is spun in a very
slight manner, and thus offers a striking contrast to those of many
other insects; in fact, it is so slight, and the meshes are so open,
that the insect can be readily seen within suspended in a hammock of
silk, and thus presenting a very curious appearance. In another, the
inclosed insect looks just like a poor prisoner within a grating.
[Illustration: _Cases formed of Epidermis of Bark._]
In order to give a sufficient degree of strength to their cocoons,
some larvæ adopt the plan of forming them partly of silken fibre and
partly of other materials. Réaumur, being on an entomological excursion
in the forest of Vincennes on a fine day in the month of May, fell in
with a most curious cocoon, formed by a larva which feeds upon the
oak-tree. At first he could scarcely conceive what the object he saw
before him was, but on removing the branch it proved to be a very
singular cocoon. Detaching a small branch, on which was a larva just
commencing its cocoon, Réaumur, finding the evening draw on, set out
on his return home. The larva did not seem to discover the fact of its
being carried away a prisoner; and as the entomologist carried the
branch with gentleness, it proceeded with its task as comfortably as
if stationed on the tree it was now leaving behind. Réaumur beguiled
the tedium of the way by carefully watching its mode of proceeding in
the formation of its cocoon. He thus noticed the larva cutting very
delicate layers of the fine upper skin or _epidermis_ of the bark of
the twig, which it fastened together by silken cords, and then formed
into two wing-like pieces fastened on each side of the twig in the
manner represented in the cut, something like the feathers of an arrow
in appearance. And now, this being done, the difficulty was to draw
the two sides together, and so to convert them into a covering for
its body. The manner in which this was done will hardly, perhaps, be
imagined. It will be best understood if the reader will cut out two
pieces of paper of the shape of these two side portions, fasten them on
with a little glue by one of their edges to a piece of twig, and then,
by a fine needle and thread, draw them together by stitching from side
to side all the way up. The larva does something very like this, for it
fixes silk cords to each of the outer edges, and then pulls and hauls
with all its might until it has forcibly bent over the layers until
they meet, and then it ties the edges together by short cords, so as
to produce a seam so beautifully close, even, and fine, as would put
the "fine-drawing" of the most superlative tailor to shame; in fact,
the join is frequently quite imperceptible. Having done this, it lines
the inside with beautiful tapestry of silk. By the time Réaumur and his
friends had got to the end of their walk, which occupied an hour and
a little more, the larva had, after vast labour, joined together its
seams, and far advanced toward the completion of its task.
[Illustration]
Réaumur made also some most interesting observations upon a larva which
constructs its cocoon of a sort of silken mesh, the interstices of
which are filled with grains of earth. Having broken off the top of
a cocoon he witnessed the singular spectacle of the larva proceeding
to mend it again. Without leaving its cell, the patient labourer put
its head out of the opening in the attitude represented in the cut,
and, after looking about for a little time, picked up, one by one,
a number of grains of earth, which it stored up in its case. After
this, it filled up the sides of the opening with a net-work of silk,
working the grains of earth into it as it proceeded. For three hours
the larva worked incessantly at its task, and at the end of that time
had materially reduced the size of the opening. Réaumur was now curious
to observe how the opening still left would be filled up, as the insect
could no longer put its head out, and he expected to see it filled up
with a mesh of silk. But he had not given the larva due credit for
ingenuity in making this supposition. It filled up the opening first,
with a mesh of silk, but between the meshes, in a most curious manner,
it thrust out some little grains of earth, which it had previously
stored up, until they actually appeared on the outside, and any one
would have supposed they had been laid on from without. It finally
ended its labours by coating the inside of the opening also with a
layer of earth. Réaumur afterwards cut the cocoon in half with a knife,
and by that means was enabled to see how successfully the larva had
repaired the injury.
We must now speak briefly of the Suspension of the Larva; and it may
be mentioned, that the insects, whose larvæ perform this manoeuvre,
are almost exclusively the butterfly tribe. There are various ways of
effecting this object. The spinning apparatus, by which the cords are
to be formed to sustain the body of the insect in the air, is situated
in the _mouth_ of the larva, and it may well be imagined that the
insect, which is about to hang itself up by the _tail_, has no easy
task to perform in having to fasten its cords to the tail, and then to
the branch above it. If a spider wished to hang itself up by the tail
it would be a very easy thing so to do, for the spinning apparatus is
placed there, and it has only to let itself fall from a branch after
first glueing the end of the cord to it; but a larva is differently
circumstanced, and it requires no slight display of ingenuity to
accomplish its purpose.
Its first process is to select a suitable leaf or twig, upon which it
weaves a sort of little mound of silk of the shape of a button. This
done, it examines it carefully to ascertain its strength, and satisfied
therewith, it then proceeds to thrust its two hind legs in amongst the
threads of which the button is composed, and in so doing it causes
the hook-like processes which fringe these legs to become securely
entangled in them. It then is safe as to the issue, and now lets its
body drop down, fearless of the most violent rockings to which even a
tempest might expose it.
Another way of suspending themselves is almost equally singular with
this. It may be witnessed by the reader if he will take the pains to
collect the larvæ of the common white butterfly, found in abundance
upon our cabbage rows; and by properly attending to, feeding and
watching them, this curious proceeding may generally be observed, in
a few at least of the number, supposing that the others may have hung
themselves up without being seen in the very act. If we were to set
a mountebank to the task this larva has to perform, it may well be
doubted whether with the richest reward before him he could manage to
effect it. First, he would have to tie both his feet fast to a branch,
so that he would swing head downwards; then, in order to hang himself
in the horizontal posture, he must bend his body up, fasten a cord
round the branch in a proper place, so as to form a loop, and then put
his head and body into it, so that it would support him comfortably
just under the arms. Probably the most supple-jointed gentleman would
find himself discomfited in the attempt. The caterpillar in question,
however, does all this, and more; for it has _to spin the ropes_ with
which it is to be suspended. Fixing its hinder part, in the manner
just described, to the little button of silk, which it first forms, it
then spins the girth, in which it intends to trust its safety, by the
apparatus of the mouth. Sometimes larvæ tie themselves in an upright
position, as martyrs to a post; but the most common method is the
horizontal one, giving the insect the resemblance of a sailor swinging
in his hammock.
[Illustration: _Horizontal Suspension._]
[Illustration: _Perpendicular Suspension._]
We must ask attention, before we close our chapter, to one more
account of the proceedings of a larva; and this too is in a common
insect--perhaps the housewife would say a little _too_ common--the
_meat-fly_. This larva, when its days in that condition are at their
close, quits its long greedily-devoured and disgusting food, and
penetrates into the earth; there it contracts its body in a singular
manner, and its skin becomes thickened and hard, so as to form a sort
of parchment-like case, _inside_ which its jaws are cast off, instead
of outside, as is commonly the rule. "Were such an extraordinary
transformation as this to happen to one of the larger animals, it would
be held forth as altogether miraculous," writes Mr. Rennie. "Were
a lion or an elephant, for example, to coil itself up into a ball,
compressing its skin into twice the thickness and half the extent,
while it remained uniform in shape and without joinings or openings:
and at the same time were it entirely to separate its whole body from
this skin, lie within it, as a kernel does in a nut, or a chick in an
egg, throwing off its now useless tusks into a corner; and then, after
a space, should it acquire wings, break through its envelope, and take
its flight through the air, there would be no bounds to our admiration.
Yet the very same circumstances in miniature take place every day
during summer, almost under the eye of every individual, in the case
of a blow-fly, without attracting the attention of one person in a
million." So much more are we attracted by great things than by small.
The work of preparation finished, the insect securely buried in its
cell or warmly surrounded by its cocoon, or hanging up to the branch
of a tree, or in any other way concealed from view or protected from
injury, little more remains to be added to the larva history. Its last
action, after settling itself in a comfortable position, is to cast off
its skin, which is generally, in the case of those larvæ which inhabit
cells or cocoons, left inside the recess: sometimes it is cast out. The
period at which the insect ceases to belong to the larva stage, and
passes into the next, varies, and will receive notice in the following
chapter.
When in the vengeance of God upon the guilty land of Egypt it
pleased Him to send the plague of insects, the exclamation of the
magicians was: This is the finger of God." Such, in an admiring
sense, may be ours also as we look back upon what we perceive God to
have done for this humble portion of His creation in the few past
pages. What provision, what wonderful forethought and wisdom has
not been exercised upon beings which man despises, or even abhors,
and which fall daily by thousands under foot, crushed and forgotten
except by a few. Let us search the green lanes and hedge-rows more
assiduously,--let us poke even into the dirtiest corners,--let us
examine well the leaves and branches in our gardens, the depths of
the purling brook, the cavities of the aged trunks, and the cracks in
the deep-furrowed bark,--let us look narrowly upon the cabbages and
nettles, as well as upon the rose-bush and myrtle,--let no place, in a
word, be beneath our scrutiny, no object beneath our notice;--let us
do this, and we shall not need to sigh after foreign scenes, or the
majestic wonders of nature, for we shall have a microcosm, a world of
wonders, in a table drawer, and an exhaustless theme of admiration in
the contents of a tumbler of water.
[Illustration: INSECTS ESCAPING FROM THE PUPA CONDITION.
Page 300.]
PART III.--THE PUPA.
CHAPTER I.
THE TRANSFORMATION.
Hanging to the slender branch of yonder rose-tree, swinging to and
fro with the gentle air which blows in scented waves through the
flower-garden, is a little object to which we wish to direct attention.
Had not notice been thus directed to it, in all probability we should
have passed it by, if we observed it at all, only considering it to be
a broken twig or withered leaf suspended by a cob-web. We may examine
it minutely, but all is quiet and motionless in the little mass, and it
is impossible to detect the least sign of life. A casual eye would rest
upon it without interest, and would turn away from it uninstructed as
to its nature and properties. In colour it has nothing to attract--it
is of a dirty white or brown, and in shape it is, though curious, so
small, and so uninviting, that few would take the trouble to pay much
attention to it. Day by day it swings from its silken cord, and is to
all appearance an object without interest to all around it.
Yet this slumbering, unattractive mass contains a living being. Though
the aspect of death has passed upon it, and though we may perhaps be
unable to detect the symptoms of movement in its parts, it is yet
alive, and the lapse of a little time will convert the slumbering
being, thus singularly hung up to be the sport of the wind and rain,
into a creature more extraordinarily active than perhaps any other in
the animal creation. While it sleeps, great changes are taking place;
it is receiving new organs, it is being matured, developed, perfected,
fitted for a nobler existence, and for a higher range of duties, than
it has yet known. Such is the _pupa_.
From these remarks it will be sufficiently evident that this chapter
of our insect history has to speak of a period when there are but
few traces of active existence in the insect, and it might therefore
be supposed there remained little to be said upon a period of the
insect's life which is only comparable to a prolonged sleep. But
entomological science is too rich in interesting matters upon every
subject to admit this conclusion, and we shall find that there is much
to be narrated which equally, with what has formerly been written, is
calculated to raise our admiration to the Great and Beneficent Author
of all Nature.
If we turn to a Latin Dictionary and hunt out the word which stands at
the head of this chapter, _Pupa_, we shall find several definitions of
it given; for example, _a little girl_, _a doll_, and _a baby_. What
have either of these to do with an insect? some will exclaim, and they
may feel disposed to consider the great Linnæus, who gave the insect
tribes while in this stage this title, to have been not over happy in
his selection of terms. But those who thus exclaim have perhaps only
seen _babies_ as they are clothed in England, possessing the power and
comfort of free movement, and having their arms and legs at liberty.
Between the aspect of these little creatures and our insects no one
can trace any resemblance. But it is very different on the continent;
there, out of the strange notion that it will keep the poor little
being's limbs straight, it is the custom to wrap babies up in swaddling
clothes, until they can neither stir hand nor foot, and they are made
to resemble Egyptian mummies as nearly as possible. Babies wrapped
up in this cruel and barbarous manner form objects of so peculiar an
appearance, that it is quite ludicrous to trace the resemblance between
them and the _pupæ_ of insects; and therefore Linnæus, as it appears,
could scarcely have selected a better epithet for the insect than its
present title of _pupa_, as it too has the aspect of being wrapped up
in swaddling bands.
[Illustration: _A Pupa._]
But, as we formerly mentioned with regard to larvæ, all insects in the
_pupa_ state are not called popularly by their scientific and correct
name. Those that are closely wrapped up, and are in fact complete mummy
insects, are called sometimes by the term _Chrysalis_, or _Aurelia_,
because they are sometimes of a _golden_ lustre, the one being derived
from the Latin, the other from the Greek term for "gold," and this
even when they are not gilded in this manner. Again, when, as we shall
presently have to notice, the insect in the _pupa_ state is still
capable of eating or moving, or when it does not lose its legs, its
popular name is a _Nymph_. As in the preceding chapter, so in this, we
shall not regard these terms, as they only create a great amount of
confusion, but shall adopt the true term, _pupa_, throughout, whether
the insect spoken of falls within the one or other of these popular
divisions, or not.
We traced the larva in the last chapter up to that period in its
history when it enters its cell, or otherwise retires to concealment,
previous to its becoming transformed into the _pupa_. Here, immured in
darkness, and alone, it is left to undergo that mysterious struggle of
the vital powers which is to end in producing a new and more perfect
creature out of one which, however perfectly adapted to its condition,
is very far inferior, as regards the completion of its organization,
to that which it is destined to become; and here we may appropriately
pause to take up the history of the curious larva so recently
described, at p. 207, as performing the feat of hanging itself up by
the tail from cords spun by its mouth; since it exhibits to us in a
striking point of view the shaking off of the old form of larva, and
the putting on of the new one of pupa. In addition to this, it is,
perhaps, one of the most astonishing instances of animal agility with
which we are acquainted.
In order to make its manoeuvres and the difficulty of them the more
easily comprehended, let us (to follow Messrs. Kirby and Spence in
the same matter) put a case of a somewhat similar kind before the
readers by way of supposition. Country fellows at wakes and fairs
frequently--for the diversion of the company there assembled, or for a
prize of some value in their estimation, perhaps a fat pig, or a leg of
mutton--run races in sacks which are tied close about their necks, and
of course tumble about a good deal, and display anything but a graceful
mode of progression. "Now," say these authors, "take one of the most
active and adroit of these, bind him hand and foot, suspend him by the
bottom of his sack, with his head downwards, to the branch of a lofty
tree; make an opening in one side of the sack, and set him to extricate
himself from it, to detach it from its hold, and suspend himself by
his feet in its place. Though endowed with the suppleness of an Indian
juggler, and promised his sack full of gold for a reward, you would
set him an absolute impossibility; yet this is what our caterpillars,
instructed by a Beneficent Creator, easily perform!"
[Illustration: _This Cut shows the entire change from the first rupture
of the skin to the casting away of the old skin._]
[Illustration: _Tail of a Pupa magnified to show the toothed parts._]
Let us proceed to show in what manner the caterpillar performs this
wondrous feat. After suspending itself in the way already described,
a little time generally elapses, during which the insect by turns
contracts itself, and then dilates again. At length its skin splits
near its head, and a portion of the pupa appears, which acts like a
wedge, and, being thrust partly through the slit, causes it to tear
still higher and higher towards the tail. The insect continues its
painful labours, swelling and contracting alternately, so as to push
the torn skin higher and higher up, as one would roll off a stocking,
until at length the old skin is folded into several rolls, and is quite
at the tail. But the task is as yet only half accomplished; the most
arduous and difficult part remains to be done. The pupa is shorter than
the larva, and consequently hangs out of reach of the silken button in
which the latter was firmly fixed by its hind legs. It seems now as
if the poor insect must fall, for there appears no way for it to get
up to the silk anchorage, and the folds of the pushed-up old skin are
all that retain it in its position, which, as may be imagined, is far
from a secure kind of fastening. How is it to disengage itself from its
case, and be suspended in the air while it climbs up to take its place?
Without arms or legs to support itself, the anxious spectator expects
to see it fall to the earth. His fears, however, are groundless; the
supple segments of the pupa's abdomen serve in the place of arms.
Between two of these, as with a pair of pincers, it seizes on a portion
of the skin; and, bending its body once more, entirely extricates
its tail from it. It is now wholly out of the skin, against one side
of which it is supported, but yet at some distance from the leaf;
the next step it must take is, to climb up to the required height.
For this purpose it repeats the same ingenious manoeuvre: making
its cast skin serve as a sort of ladder, it successively, with its
different segments, seizes a higher and a higher portion, until in the
end it reaches the summit, where with its tail it feels for the silken
threads that are to support it. The tail is provided with a number of
minute hooks which catch in the meshes of the silken button, and the
pupa, thrusting it into the meshes of this button, feels quite secure
as to the result, and drops safely into the perpendicular position,
dangling in the air as gaily as did the larva before it. But its old
skin still clings to it, and seems greatly to annoy it by its presence;
so much so, that it sets about attempting to cast it down altogether.
As it will be remembered that the legs of this skin are still firmly
attached to the silk, in consequence of their hook-like form, it will
be evident, that this also is a task of some arduousness. In order to
get rid of it, it jerks itself about in various directions, and spins
round very rapidly,--doubtless the reader has often seen the insect in
this act, and has wondered what was its object in whirling round after
this manner,--by this means at length the cast-skin appears loosed
from its hold and drops off. The whole proceeding from first to last
is represented in our engraving. The little hooks of the tail of the
pupa are represented in the adjoining cut much enlarged. Well does
Réaumur exclaim,--"These manoeuvres of withdrawing its tail from the
old skin, of climbing up the old skin, and of hooking its tail in the
silken button,"--and, as we might add, of whirling itself, and in other
ways agitating itself to get rid of its old skin,--"are manoeuvres
so delicate and perilous, that we cannot help wondering how an insect
which only executes them once in its life, should execute them so
well; and we are led to the inevitable conclusion that it has been thus
taught by a Great and All-wise Master."
The manner in which other larvæ cast their skins and become pupæ when
they enter their cell cannot be described, as they perform this act
in all the privacy and darkness of their solitary habitations; but in
all probability it differs in no respect from the manner in which the
same creatures cast their skins when they moult, excepting that the new
being which emerges from the cast-skin is no longer a larva, but a pupa.
The time occupied by the creature in its process of change differs
in different species. In some it is short, in others it is long.
Generally, it does not exceed a few days. We are told, however, of the
larva of some insects which are six months before they become pupæ. The
Baron de Geer tells us with surprise of the larva of a moth which he
had watched. It became a larva, and spun its cocoon, in the month of
August, 1746, and was attentively kept during the winter. The spring
came, but the larva still remained a larva, and did not show any signs
of changing its form; and winter came again, finding it still a larva:
the second winter passed, and it was not until April 1748, that is,
more than eighteen months after it first became a larva, and entered
its cocoon, that it underwent the change, and became a pupa: some time
afterwards it became a perfect insect.
CHAPTER II.
WHAT IS A PUPA?
But it may now be asked, What is a pupa, and what are the differences
between it and a larva, and between it and the perfect insect? It is
very necessary that this should be clearly understood; and to that end
we shall endeavour to render our explanation as simple as possible.
But it will be far better than the best description, if the reader
will be persuaded to watch these changes throughout himself. The
butterfly tribe furnish the very best illustrations in the world; and
by merely collecting a few caterpillars from the way-side, or from
the kitchen-garden, a source of amusement will be opened which will a
thousand-fold repay the trouble and time consumed in the occupation.
Of all other ways, personal observation, when it is so readily to
be effected as in the case of these insects, is the best and most
impressive method of becoming acquainted with the "Life of an Insect."
Such knowledge is far more entertaining than book-knowledge, and is
much more agreeable to acquire, and more easy to retain.
We must guard our definition of what a pupa is, by reminding the reader
that some insects with which he is very familiar do not pass through
this change in the same manner that the majority of insects do; that
is, in a state of torpor or sleep. If he were to rear up a spider from
the egg, and were to watch for the time when it would become a still,
lifeless-looking object, like that which we have called a pupa, he
would assuredly be disappointed, and he might accuse this little work
of leading him into error, because it declares that all insects must
pass through the pupa state before they become perfect in their form
and number of their parts. Yet that very spider has passed through
both the larva and the pupa state under the observer's eye without his
being able to recognise the fact, simply because in both these states
it is very like the perfect insect, and can walk about and eat just
as usual. In fact, it is more than probable that spiders of the same
kind in these different conditions could scarcely be recognised so
as to say that they were pupæ, or perfect insects, even by tolerable
entomologists; and it is very likely that mistakes of this kind have
often occurred.[I] We learn, therefore, from this statement, that some
pupæ are active, and move about just as they did before, although they
_are_ in the pupa state.
In a great number of cases, then, a pupa is a state in an insect's life
when it rests from active exertion, and from taking food, and when,
underneath the dry and withered skin, a series of great changes are
taking place, which are preparing it for its future life in the perfect
state. Thus it differs from the _larva_ state in not eating and moving,
and in the important particular,--that it is receiving new parts and
organs, which are added to it under the skin. It also differs from the
_perfect insect_ in the same respects as in the first place from the
larva, and also in the important circumstance, that the perfect insect
the moment it enters that state, has no more organs added to it--it
is, in fact, perfect, while the pupa is imperfect. Let us place these
differences in a tabular form:--
The Larva The Pupa The Perfect Insect
Moves about and eats. Does not move about Moves about and eats.
nor eat.
Has no new organs Has no new organs
added to it beyond Has several new organs added to it, beyond
those acquired in the added to it, to prepare those obtained in
egg. it for the perfect state. the pupa state.
Let us repeat our caution, that this definition is only applicable
to _inactive_ pupæ. In the active pupæ the same development of new
organs takes place, but it does not interfere with the usual actions
of life. We must also add, that some of the pupæ which we must call
inactive, nevertheless are not wholly without motion, but are capable
of manifesting that life is in them, death-like though they appear,
by slightly moving the lower part of the body.[J] All inactive pupæ,
however, are without the power of moving about.
At the risk of being thought tedious, it has been indispensably
necessary to be thus precise upon this point; a little careful study of
these two or three pages will fix the distinctive characters of the
pupa firmly in the reader's memory, and will enable him to find the
account given of its history clear, easy, and interesting.
Having thus defined what the pupa state is, let us take up one of these
withered objects, and by a little gentle treatment, with the assistance
of a delicate scissors, a sharp pointed penknife of very keen edge,
and two or three pins, we shall succeed in unrolling the insect mummy.
In order to obtain the best sight of what the pupa case contains, it
will be advisable to select as large a pupa as can be procured. Those
of the butterfly tribe are well suited for this purpose. If we are
pretty fortunate in our dissections, we shall succeed in discovering,
that within the membrane-like skin there is exhibited a beautiful
spectacle of order and neatness. The legs, and wings, and other
external appendages, are folded down close to the body of the insect.
The feet are often crossed smoothly over the breast, and the wings are
flattened against the side of the body; the antennæ are also neatly
arranged parallel with the legs; and altogether the insect presents a
very singular appearance, from the fact of all its organs being thus
smoothed down, compressed into the smallest compass, and enveloped
by the external skin. The mummy appearance is very striking in some
pupæ, as in the specimen figured. The appearance of the folded limbs
is indistinctly exhibited in the companion pupa. All the parts of the
perfect insect can be distinctly traced, if the pupa is sufficiently
matured.
[Illustration: _Pupæ._]
By gently using a fine needle, the wings, antennæ, and legs, can be
separated from the side of the body, and made to exhibit somewhat of
their natural appearance; but as yet every part is widely different
from the corresponding parts in the perfect being. The legs are
shapeless, the antennæ are imperfect, and the wings,--those glorious
organs of the complete condition,--are as yet devoid of their splendid
tints, being of a greyish colour, and exhibiting little resemblance to
the elegant form afterwards to distinguish them.
Strange to say, every organ in this pupa is enclosed in a sheath of
membrane. The head of the insect is covered by a case; the delicate
antennæ, however long or fine, have their cases, or sheaths; even the
eyes are provided with them. They exist also upon the trunk, wings, and
legs, and _tongue_, or proboscis. These cases must not be mistaken for
the general outer case which covers the whole insect; they are separate
from that, and cover the organs in question closely, after the manner
of a glove.
If we were to open a pupa within a few hours after it had assumed this
state, we should find its interior filled with a milky fluid, in the
midst of which its future limbs and organs are seen very distinctly,
but are as yet in a most fragile, or even half fluid state. At a little
later period this fluid disappears, and hardens into a sort of glue,
which partly fastens down the tender limbs into their proper position
until the appointed time comes for the insect to burst from its sleep
and live, and from which the case which covers them is formed. From
the account thus given of the contents of the pupa-case, it will be
apparent that the pupa possesses, when perfect, all the organs of the
complete insect, head, eyes, antennæ, wings, legs, &c., and is in fact
only different from it in that it is still inactive to a great extent,
and still a prisoner within its cell of membrane. In a little while
the bonds which keep it in the tomb will be broken, and the slumberer
shall rise a glorious creature to the enjoyment of all the happiness of
a new condition of existence.
[Illustration]
Perhaps few things would cause a person ignorant of insect life more
amazement than if we were to hold before his eyes some of the varieties
of pupæ in one hand, and the perfect insect in the other, and were
then seriously to assure him that both were the same creatures in
reality. "Can it be possible?" he might exclaim. "This dry, brown
little mass, with these singular knobs, and this elegant insect with
its gaudy wings and delicate figure--these the same being!" Nor when
we look at the various figures of pupæ, should we be much surprised at
his exclamation. In one of the cases at the British Museum is a very
large pupa which we have had engraved, and which is here presented to
the reader. In this curious creature the folding up of the limbs is
very obvious; and some idea of its strange aspect may be formed from
the representation of it here given. The pupæ of several moths are
very singular in shape. In some there is a sort of little hook, which
sticks out from the head, and seems as if it were intended to hang up
the creature by. In others there is a kind of nose attached to the
head, giving it a droll appearance. The cause of these protuberances is
the long tongue of these moths, which, as it is much longer than their
bodies, could not of course be contained in the pupa case, unless it
was folded up; it is, therefore, neatly folded up and packed into these
receptacles, where it is stowed away until, by the insect awakening
to active life, this singular instrument becomes necessary to them,
when it is withdrawn. The older naturalists, who loved to find out
mimicries of all kinds in nature, used to be fond of painting pupæ
with human faces, on account of the frequent resemblance to a Roman
nose which is found among them. Goedart, a celebrated naturalist, has
drawn several, which we are sure will excite the merriment of our
readers, and we have therefore shown these remarkable creatures _as
represented by him_ in the adjoining cut. One is a respectable-looking
old gentleman's face, with his hair brushed up very primly off his
forehead. Another resembles a mermaid, for it has the head of a lady,
and something like a cap, but its tail is more like that of a fish.
The others are quite caricatures. It is the introduction of a dot, to
represent the eye, which gives the resemblance to the face in these
figures; without it they are by no means strikingly like the face.
Madame Merian has favoured us also with some very curious drawings of
pupæ of the insects of Surinam, which appear more natural than those of
the last author, and present a very fantastic aspect, by reason of the
curious projections which stick out from their heads. A few of these
are represented below.
[Illustration: _Pupæ after Goedart._]
[Illustration: _Curious Pupæ. From Madame Merian's work on the Insects
of Surinam._]
As in the case of the larva, so with the pupa; if it is found in a
dark situation, it will probably be destitute of colour, or, at any
rate, it will only be of a yellowish white: such pupæ, when taken out
of their natural hiding-place, and exposed to the sunlight, become of
a dark colour. Indeed the majority of pupæ are without any of the gay
colouring which distinguishes the previous condition of the insect.
It seems as if it had been thought unnecessary to deck in gorgeous
raiment the cerements of what we might call "the tomb" of the insect.
But there are some beautiful exceptions to this rule. The pupæ of
most butterflies, which are suspended in open day, are of a green or
yellowish brown colour. Some, however, are painted in fairer colours;
and a still greater number are speckled with glittering spots of
golden hue, and shine as though gilded with the purest leaves of that
precious metal, and burnished. Hence, as before explained, the Latin
and Greek terms of _aurelia_ and _chrysalis_ for the pupæ of these
insects. The gilding makes them very attractive objects, being applied
now in streaks, now in spots, and occasionally,--and this in the very
common pupa of the butterfly whose caterpillar, or larva, feeds on the
nettle,--they are entirely covered with this splendid coat. The shade
of gilding ranges in the depth of its tone from a very pale yellow
to the full lustre of virgin gold. No wonder that those who mistook
the object of chemistry, in trying to turn all things into gold, were
attracted by these glittering things, and actually believed these
spots to be of real gold, and hence imagined that they had found out
an argument in nature for the transmutation of common metals into that
coveted one. But a little experiment, which it is in the power of any
one to perform, would soon have undeceived them, and taught them the
truth of the proverb, "All is not gold that glitters." By infusing a
portion of saffron in hot water, and straining it off after a little
time, and adding to the rich yellow liquor thus obtained a few lumps
of pure gum Arabic, a sort of gilding varnish will be obtained, which,
if applied to a bright shilling, will give it very much of a golden
appearance, owing to the shining of the metal showing through a
transparent film of a golden colour. The gilded look of the pupa was
found by Réaumur to be produced in the same way by the shining white
membrane of the inner skin showing through the outer skin, which is of
a transparent yellow.
In the Transactions of the Linnæan Society for 1833, the Rev. L.
Guilding describes a very curious pupa, the case of which resembles
pearl. These little bodies are found in abundance in the island
of Antigua, and are often sent home to Europe, under the name of
"ground-pearl," as distinguished from the ordinary fishery-pearl.
They are devoured by turkeys, and fowls, until the birds are nearly
choked with them, when the remedy is to pour vinegar down the throat,
which dissolves the pearls, and sets the poor bird at ease. They are
strung into necklaces and purses by the ladies of the Bahamas. They
long caused much perplexity to naturalists; but they were ultimately
found to be really only the pupæ of a little insect which appears to
infest the ants, those voracious creatures, and thus to keep down their
numbers. A representation of the ground-pearl, and the insect within,
is annexed.
[Illustration: _Ground Pearl. The Insect and its Case magnified._]
CHAPTER III.
RESPIRATION OF THE PUPA.
Having glanced at these particulars in the history of the pupa, we come
to the important question,--Does the pupa, in this torpid condition,
still breathe, as the larva did, or not? On a careful examination we
might detect, with the help of a magnifying glass, the same breathing
holes or _spiracles_, spoken of on page 161, as appertaining to the
larva; and were we sufficiently skilful to dissect the pupa, we should
find much the same arrangement of air-tubes within the body. In the
absence of all other means of ascertaining the fact, we should be
warranted in concluding from the presence of these organs alone, that
the pupa has the faculty of breathing, no less than the larva. M.
Réaumur has given a beautiful description of the breathing-holes, or
spiracles, of the pupa, and has represented them in an engraving, of
which a copy is furnished at page 161. He found that they are protected
by little valve-like contrivances, just as our mouths are protected
by our lips; and these can be opened or closed at pleasure by the
creature; so that if plunged into water, that fluid cannot enter the
insect's body, for all its little doors--and there are no fewer than
eighteen of them!--are fast shut. Singular to say, however, if plunged
into oil, the oil has the power of entering them, and the pupæ may be
thus drowned.
It is very easy to put the fact of the breathing of the pupa, inanimate
as it appears, to a certain test. By taking a wine-glass half full
of water, and putting it under an air-pump, and then exhausting the
air, we shall be able to extract the air which exists dissolved in the
water: or some water that has been boiled and allowed to cool will do
as well. If we now put a pupa into this water, and again exhaust the
air from the receiver, we shall notice, at the second stroke of the
piston, a number of little jets of air come from the insect's body at
the places where the spiracles are situated, thus clearly proving that
the creature breathes air by this apparatus. The fact may be tested
also in another way--and both this and the preceding experiment are
due to the ingenious Réaumur. He took the pupa of a butterfly, and
suspending it by a thread immersed it half way down in oil; on taking
it out after some time it was still alive and apparently uninjured, the
reason being, that the entire number of its breathing-holes were not
covered. He took another of the same species, and plunged it entirely
under the oil, and taking it out after a time it was found to be quite
dead; in fact it had been suffocated by the air being shut out from
its breathing apparatus, and that as effectually as if it had been one
of ourselves lying at the bottom of the sea. We may say, therefore,
with perfect accuracy, that though the pupa, this seemingly un-living
object, neither moves nor eats, nor in any other way gives us a sign
that it is alive, except in a few cases, and that in its advanced
stages, we can, nevertheless, prove it to be living; as it can be shown
that it has the power of breathing; and if it breathes, it lives.
We may take the liberty of appropriately appending to this statement a
most interesting and delightfully-told anecdote, from the pages of the
Baron de Geer, of an insect whose larva lives in the water, but whose
pupa is an air-breathing creature, and consequently would perish if the
change from larva to pupa were to take place under water, without some
especial contrivance to furnish it in the pupa form with a supply of
air. Yet how can this be, when the insect is under water the whole time
up to its becoming a perfect moth? We shall hear:--
"At the commencement of spring, as soon as the frost and ice had
disappeared, I sauntered out one day to procure some fresh plants from
the bottom of a stream, in order to feed some of my caterpillars with
them. Between the leaves of these aquatic plants I presently found a
large number of aquatic larvæ, which had there safely passed through
the rigorous season just gone by. I took a number of them, and put them
in some boxes, where they eat the leaves with which I fed them. There
they grew larger from day to day, although by slow degrees. I tended
them until June in the same year without perceiving any other change
in their appearance than that they had grown to a considerable size.
But at the commencement of this month I noticed that they became very
uneasy; they forsook their leaves, and wandered about the sides of
the boxes, which contained water. Sometimes they would creep out of
the water, and again would go into it. They seemed as if they were in
search of something which they had lost. It was now evident that their
object was to find some convenient place in which to undergo their
transformation into pupæ, but they did not like the boxes in which they
were confined, and several even died. I began to despair of seeing
their metamorphosis; which gave me much regret, as I had a great desire
to become acquainted with their whole history. In order to satisfy
myself, I went on the 26th of June to the spot from whence I had taken
them, in order to discover, perchance, some larvæ about to become pupæ,
and to ascertain the places they selected in which to undergo their
change. I had the gratification of being completely successful, and
of discovering not only the larvæ, but even several of them which had
shut themselves up in silken cocoons, and had not yet undergone their
transformation.
"The month of June appears, therefore, to be the period when these
larvæ prepare for their change of form. They do not leave the water
to accomplish it, the change taking place under water. They attach
themselves to the leaves of some of the younger aquatic plants, which
are at a suitable depth from the surface of the water. By means of
several silken cords the insect fastens together two, and sometimes
even three leaves, between which it spins an oval cocoon, composed
of very white silk. This cocoon is of a double structure; the true
inner cocoon, which is very white, is placed within an outer envelope
of silk, of a greyish or brownish colour. The envelope extends
considerably beyond the sides of the true cocoon (which lies loosely
in it); and towards one end there is a wide opening in it, the inner
cocoon being perfectly closed in on every side." The cut on the next
page represents the perfect insect and the pupa thus carefully provided
for.
[Illustration: _The Cut represents two leaves, between which the Worm
lies, the Cocoon itself, and the Larva._]
In this inner cocoon there is not so much as a single drop of water!
The pupa could not exist in it if it were not full of air; and the
difficulty is how to fill a little cell with air which is already
buried many inches under, and on every side surrounded by, water. De
Geer states that he did not find a particle of water in all the cocoons
which he opened. In order to ascertain whether or not it was really
necessary for the pupa to be thus carefully housed in a silken ball
full of air beneath the water, he took out several pupæ and put them
into some water in a saucer. At first they swam, but presently they
sank to the bottom. They lived for several days, but ultimately every
one died, showing plainly that the air-cell was absolutely necessary to
their existence.
[Illustration: _Pupa and perfect Insect._]
Yet, although these pupæ were air-breathing creatures, strange to
say, De Geer found that if taken from their little cells out of the
water, they shrivelled up and died. He put several in a dry box, and
invariably found that in a short time they were dead. He imagined,
with great probability, that the cause of their death was the
evaporation of their fluids, which of course does not take place when
they are enshrouded in their cocoons, and surrounded on all sides with
water. He made one more experiment with them, which was as follows:--He
took several out of their cocoons, and placed them in water in such a
manner, that one of their sides was in the air, while the other was in
the water; he kept them for a considerable time in this position, and
he had the pleasure at its expiration of seeing them become perfect
insects, just as if they had never left their cocoons. The necessity of
both air and water to their well-being was thus clearly proved.
How can we sufficiently admire the ingenuity and skill displayed by
this insect in the execution of its difficult task! When a human
engineer wishes to build under the water, he must have recourse to
the most cumbrous and powerful mechanism to enable him to effect his
object. Piles must be driven into the bed of the river so closely
as scarcely to allow any water to come through; a steam-engine must
be fixed close by, to pump out all the water from the space thus
enclosed; and a number of men must labour hard to stop up the chinks,
where the water comes pouring in. Thus men, and machines of great
power, and in sufficient number, are requisite to enable the most
expert engineer to form a cavity at the bottom of the river's bed.
What if we were to give him as a problem, to build a cell which should
be perfectly water-tight and filled with air, without allowing him
to employ any of these means, and to insist that it should all be
done without his coming up to the surface of the water at all for
anything? He would probably tell us it was impossible. Not so the
insect; it, though on all sides surrounded with water, actually spins
a web in the waves, and fastens it by cables of sufficient strength to
adjoining plants, and afterwards forms a water-tight cell in which it
shuts itself safely up secure against the invasion of enemies, or the
intrusion of a drop from the element in which its cell floats and is
moored.
[Illustration: _Pupa of the Ephemera, showing its gill-like Organs._]
All pupæ of aquatic habits do not, however, possess this remarkable
faculty of surrounding themselves with air even in the midst of the
water; and these would certainly perish unless means existed for them
also to inhale the vital air. These means are found in the endowment
of them with the power of swimming. Surely our readers must often have
seen the wriggling movements of certain little blackish objects, which
are to be found in every stagnant puddle in the summer. Many of these
are the pupæ of various species of gnats; and when we watch them come
darting upwards by a succession of flaps with their tail, until they
reach the surface, where they remain for a short time, we see the
means by which, although they live immersed in water, they are enabled
to breathe the air. For if we scrutinized them a little narrowly, we
might detect on each side of their largest extremity or head, a pair
of minute tubes which open into the air at the surface of the water.
It may sink beneath the water for a time without inconvenience, and it
is soon found plunging upwards, anxiously seeking to thrust its tubes
into the air. In the _larva_ state the gnat breathes by its tail, in
the pupa state by its _head_! The pupæ of some aquatic insects breathe
like the larvæ of the same insects by organs like gills. That of the
ephemera shown on the last page is an instance.
The curious apparatus of a telescope-like air-tube of the rat-tailed
insects, described in a former page, will not be forgotten by the
reader. It may interest him to learn that there is another little
creature which, in the pupa state, is furnished with a somewhat similar
apparatus. These pupæ have not the same power of swimming with the
last, and therefore require a special provision to meet the necessities
of their case. They are plunged some way down in the water, and air is
conveyed to them by a hollow tail-like tube, which is always found to
open on the surface of the water. It is a curious thing to contemplate
these little creatures, so beautifully provided for in this manner.
Secure of all they need in the supplies of air furnished to them by
their tube, they rest peacefully in the waters, unmoved by any of the
accidents which occur to surrounding creatures, and patiently awaiting
the hour which is to behold them rise from their watery bier, never
more to return. Let us so likewise rest in assurance of our Heavenly
Father's love and care for us, knowing that every want will be supplied
to his children by Him, who has said, "I will never leave thee nor
forsake thee."
CHAPTER IV.
VARIETIES AND AGE OF THE PUPA.
Although we are anxious not to attach too much importance to mere names
in this little work, and rather to keep the reader's attention fixed
upon the really essential truths of the "Life of an Insect," it is
expedient that we should mention that while all pupæ may be divided
into the two classes, _active_ and _inactive_, yet there are several
very striking variations in them, which are more remarkable than
those of larvæ. These it is proper here to mention, in order that the
reader may be spared the perplexity which would otherwise ensue, were
he to imagine that all inactive, or all active pupæ, were pretty much
alike. Let it never, however, be forgotten, that it is no matter what
the variation in form may be, nor does it matter whether the insect
is active or inactive, while in this state of passage from the larva
to the perfect form, it is always neither more nor less than a pupa.
Through this stage all perfect insects pass, although they may put
on various forms and aspects while they are in it, and may possess
various, and, perhaps, very opposite faculties during its continuance.
If this important fact is borne in mind, there will be no risk of being
misled by the confusion of sounds and names, which some have been
pleased to encumber insect history with.
In order to form a clear conception of these variations, reference may
be made to the engraving on the next page, in which we have caused to
be represented the five different kinds of pupæ, as they were named
and classified by Linnæus. This plate will sufficiently manifest the
necessity of an explanation upon the subject of the variations of pupæ;
for few persons in examining it would form the remotest idea, that
all the insects there represented are really and truly in the pupa
state. Some look so like the perfect insect, that it would be almost
impossible for any one only slightly acquainted with insect history to
believe them to be in what is in reality a transition stage from the
larva to the perfect form.
[Illustration: _Various forms of Pupæ._]
I. The insect, No. 1, is a pupa called the _Complete_, because it is
_active_, and has many of the parts of the perfect insect. The pupa of
the spider is an instance.
II. The insect, No. 2, is a pupa called the _Half-complete_, or
semi-complete. It is also active, resembles the perfect insect, but has
only the rudiments of wings. The grasshopper is an instance of this
kind of pupa.
III. The insect, No. 3, is a pupa called the _Incomplete_. It is
_inactive_, but possesses rudiments of legs and wings. The common wasp
is represented as an example of this kind.
IV. The insect, No. 4, is a pupa called the _Obtected_.[K] This pupa
has its upper portion encased in the peculiar manner represented, the
chest and lower portion being distinct. The butterfly pupa belongs to
this division.
V. The insect, No. 5, is a pupa called the _Coarctate_.[L] In this case
the pupa is enclosed within its larva skin, which forms a globular
or oval case, the pupa lying loosely in it as if it had shrunk to a
smaller size. The pupa of the blow-fly is an example.
Such are the five variations of pupæ, as they were recognised by
Linnæus--the _Complete_, _Half-complete_, _Incomplete_, _Obtected_, and
_Coarctate_. They are sufficiently minute for ordinary purposes: and it
will possibly save the reader some confusion of ideas to endeavour to
fix them in the memory; so that when looking at an insect whose pupa
state may not be so very characteristic as that of the blow-fly, or
butterfly, he may still be able to say with confidence, that although
it is unlike these, it is nevertheless a pupa. On all subjects nothing
is of so much importance as clearness of ideas. It is better to know
only a few things, and to understand them clearly, than to have a
confused and indistinct knowledge of a great number. It has been,
therefore, simply and entirely with a view to obviate this state of
things in the mind, that these definitions of the different kinds of
pupæ, which may have appeared not altogether interesting, have been
given.
Having fulfilled this duty, we may now proceed to the more agreeable
task of ascertaining some interesting facts relative to the insect's
life and age in the pupa state. We have already seen that the insect in
the larva state often arrives at a very respectable old age; indeed,
in this state insects live longer than either in the pupa or perfect
states. But pupæ also attain to a very fair number of days, sometimes
living as long as two years in that state. Often, however, they are
not more than a few days in this condition, and the insect, after a
short repose, springs forth a new and active being. But it has been
found that insects live a longer or shorter period in the pupa state
according as the temperature of the air is cold or hot. Thus, for
example, when the larva of a moth has become a pupa in the early part
of summer, the pupa state will generally not last beyond a fortnight.
But if, on the other hand, the larva becomes a pupa late in the autumn,
the pupa state will last until June in the next year: thus manifestly
teaching us that according as the weather is mild and genial the pupa
state will be shortened; or according as it is cold and rigorous it
will be increased in duration. The ingenious Réaumur determined to put
these singular facts to an experimental test; and as his results are
in the highest degree interesting and important, we shall proceed to
submit an abstract of them to the reader's notice.
In casting about for the means of exposing the pupæ he was about to
experiment on, to a warm and equable temperature, Réaumur determined
to conduct his first experiments in the Royal Conservatories, which
were always carefully heated, and in which, as he with French _naïveté_
expresses it, "summer reigned in the depths of winter." In the month
of January he carried thither a number of boxes containing pupæ of
different species. The result was precisely what he had expected:--in
the midst of a severe winter a number of butterflies appeared in his
boxes, many of which would not naturally have made their appearance
until the months of May, August, or even September; thus shortening the
pupa state from four, seven, or eight months, to a fortnight, or to
five, or to six weeks in different instances. Five or six days seemed
to be equal to a month of the natural temperature. The butterflies thus
developed were in no respect different from those which are brought
into activity at the natural period. They were as active and perfect,
as if their time and place of birth had been the green fields, instead
of amidst the strange vegetation of these splendid Conservatories.
Several of the mother insects deposited their eggs, accomplishing the
last act of their existence as if summer had come, and died while
the frosts and snow held all external nature yet in bondage. Not
only, therefore, was the duration of the pupa state in these insects
shortened, but their whole life was thus abridged by several months.
In November of the same year Réaumur recommenced his experiments,
and again exposed a number of pupæ to the genial influence of these
hot-houses. The result was the same. In the first week in December
butterflies appeared, which would not, in natural circumstances, have
been developed earlier than the May of the next year. There were some
pupæ, in particular, whose development he watched with great interest.
These pupæ belonged to a beautiful species of moth, which has two
broods in a year; that is, it lays eggs in May which become butterflies
in July, and then again lays eggs which become pupæ in August or
September, but do not become butterflies until the following June. He
was curious to see whether this second brood, instead of waiting for
several months, would, like the first, disclose its butterflies in a
considerably shorter time, now that it was exposed to the warmth of
the Conservatory. Such actually proved to be the case; and thus two
generations of these butterflies were obtained in one year. Alluding to
the depredations of caterpillars, he quaintly remarks, "This certainly
is not a secret which appears very profitable at present; but who can
tell whether that which is useless to us to-day, may not possibly
become of value to-morrow? Could we discover some new species of larvæ
which would supply us with as good a silk as that of the silk-worm,
and might be more easy to rear, but which only produced one generation
in each year, and if it lived upon leaves which could be found all the
year through, we might avail ourselves of this means of increasing the
number of its broods." This remark deserves much consideration.
He was now anxious to try whether, by applying a more equable method
of warming, he could succeed in hatching pupæ as he had done in the
hothouse. The idea occurred to him of endeavouring to hatch them _under
a hen_. He concluded that the warmth of the mother's breast would quite
as easily hatch the insects, as it does the eggs. But there was this
obstacle in the way: How could he prevent the fragile and tender bodies
of the insect pupæ from being crushed and killed by the weight of the
hen's body? and, as we would also suggest, How could he ensure that the
bird would not actually have eaten up the objects of his care? Aware
of the fact, that, when a hen is in the humour to sit, she will often
allow smooth stones to be placed among her own eggs, he anticipated
no difficulty on that score, and he hit upon the following ingenious
experiment:--He procured some hollow glass balls which he had caused
to be made as nearly as possible similar in size and shape to the eggs
themselves. Into these, by an opening at one end, he introduced seven
or eight pupæ, and stopped the mouth up with a cork, but so as to
allow a free communication with the external air by paring off a piece
from the side of the cork.
Thus prepared, he put the glass egg together with the others in the
nest. The hen was a little more sensible than Réaumur had given her
credit for; and though she did not thrust the egg out of her nest,
she removed it to the outside, where she was so obliging as to permit
it to remain; and as it was here just as warm as if it had been in
the centre of the eggs, Réaumur did not attempt to interfere with her
arrangements. A great deal of moisture arose from the bodies of the
pupæ, and condensed like dew on the sides of the glass; but after a
day or two this disappeared. The reader may now be anxious to learn
the result of this experiment. It was equally successful; indeed, it
was more so than the preceding, for in the afternoon of the _tenth_
day a pretty little butterfly was seen within his glass egg, being the
first that had appeared of the eight pupæ, and the first ever hatched
under the bosom of a hen! The remaining pupæ, all but two, appeared
soon after; these two died. Perhaps the warmth of their glassy cell
was too violent for them, for it was found by the thermometer to be
two or three degrees above blood heat. The whole six pupæ were born
in less than six days, while others of the same species in a box in a
window-seat were not developed until twelve days later. As the heat
thus obtained seemed too violent for pupæ to be artificially reared
with success, Réaumur suggests that many variations might be made
in the experiments, which would have the effect of moderating its
amount. These experiments decided in the most satisfactory manner the
quickening influence of increased warmth upon the pupæ of insects.
Réaumur now became anxious to try the effects of the opposite state of
temperature, and to ascertain whether exposure to cold would exercise
any effect upon the pupæ. It was reasonable to imagine that as warmth
had hastened forward their development, cold would retard it.
Réaumur determined to try what would be the result of putting his pupæ
in their boxes in a cellar, and taking proper care to preserve them
from the damps of such a situation. He put them there about the end
of January. In ordinary circumstances these pupæ would have become
butterflies in the month of July in the same year. July came, and
we can conceive the curiosity with which the ingenious experimenter
went down, as he tells us, to his cellars, to see if any change had
taken place in the pupæ. July passed away; August also passed by,
yet the pupæ still slumbered on in their original form. Réaumur left
Paris in September, and did not return until the November following.
He immediately went in quest of his pupa-charge, and found them still
unaltered. Were they dead? Placing one in his hand, it soon began to
exhibit such symptoms of motion as plainly showed that it was alive.
Winter closed over them still in the pupa form. The spring of the next
year dawned upon them, but they were insensible to its influences. "And
even now," cries Réaumur, in the month of August, just two years from
the time they left the larva form and became pupæ, "they are in perfect
health, in excellent condition, and would all become butterflies very
soon if I were only to expose them to a warm summer's influence."
"These extraordinary facts," observe Messrs. Kirby and Spence, "lead
us to a very singular and unexpected conclusion,--that we have the
power of lengthening or shortening the life of many insects at
pleasure--that we can cause one individual to live more than twice as
long as another of the same species, and _vice versâ_. Had Paracelsus
made this discovery, it would have led him to pursue his researches
after the elixir of immortality with redoubled confidence, and would
have supplied him with an argument for the possibility of prolonging
the life of man beyond its usual term, which his sceptical opponents
would have found some difficulty in rebutting. Even the logical Réaumur
seems inclined to infer from it, that this object of the alchemist's
was not so chimerical as we are wont to conclude. He confesses,
however, that, if it were to be attained only by the same process as
effects the extension of an insect's life,--by prolonging its state
of torpor and insensibility,--few would choose to enjoy it on such
conditions. The man of pleasure might, perhaps, not object to a sleep
of a hundred years, in the hope of finding something new under the
sun when he awakened; and an ardent astronomer would probably commit
himself with scientific joy to a repose as long and as sound as that
of the Seven Sleepers, for the chance of viewing his predicted return
of a comet on stepping out of his cave. But ordinary mortals would
consign themselves to the perils of so long a night with reluctance,
apprehending a fate no better than that which befel the magician who
ordered himself to be cut in small pieces and put in pickle, with the
expectation of becoming young again."
But this is in every respect erroneous as a deduction from these
experiments on insects. It must not be forgotten, that these
experiments were made at a time of the insect's life when it is
naturally torpid, and not upon the perfect insect. Had Réaumur
attempted to prolong the life of a butterfly, he would have failed
completely, that is, if he had adopted the same means; so that all
which we can infer from these results is simply this, that we can only
prolong or shorten the pupa state, which is a state of torpidity, a
kind of half-way between life and death.[M] The human frame knows no
such state after birth as can be properly compared to the inactive
pupa state of insects; and consequently all reasoning founded on what
may take place in such a state under the particular circumstances
described, is without foundation. Besides all this, God has himself
fixed a limit to human life; and we are expressly assured by his word
of truth, that "it is appointed unto man once to die;" and though by
reason of strength we may reach far into a long life, yet the hour
comes at last, and the green earth closes over the only mortal portion
of a man. Undoubtedly had Réaumur prolonged his experiments, he would
have found that death, or the transformation of the pupa, would
ultimately have taken place.
As yet, we are not aware that any practical results on a large scale
have followed from Réaumur's interesting experiments. It has been
already remarked, that in countries where the silk-worm is reared, it
is the custom to hasten the hatching of the eggs by women carrying
little packets of them about their person. But this is only to
bring forward the development of the larva state. Perhaps the time
anticipated by Réaumur may arrive, when insects may be hatched under
hens! or in hatching machines, so as to obtain two instead of one
brood of eggs and larvæ in a season. Réaumur suggests that the great
and wealthy who have good hot-houses, might give all the appearance
of summer to them by introducing pupæ in winter, which would soon be
hatched, and butterflies or other insects might be seen flying about
in December or January, from flower to flower! But he forgot that
gardeners generally are rather averse to the presence of insects at
all, and particularly to the all-devouring larvæ of many species of
butterflies, which would soon commit sad havoc among their choicest
plants. We may recommend such experiments to the reader as highly
interesting and easy of performance in a common sitting-room, where a
fire is kept in winter, with no other apparatus than a tin-box, or a
glass jar of very moderate size; even a pill-box would answer every
purpose.
Some curious experiments on pupæ of another kind were also performed
by Réaumur. He varnished them over with various varnishes, and found
that the pupæ thus varnished were developed several weeks later than
others of the same species unvarnished. He tried similar experiments
upon eggs, and found that the eggs of a hen would keep fresh for a very
long period if they were entirely coated with some kind of varnish.
This proved a most useful experiment, for it is now common all over the
Continent to preserve eggs by covering them either with oil or butter.
We may learn, in reflecting upon the facts brought to light by this
ingenious entomologist, with what admirable care and skill the Great
Creator has arranged the period to be occupied by the insect in the
pupa state. It has been wisely ordained by these arrangements that the
insect shall not be developed until the season when its proper food is
to be found, or when a proper position for placing its eggs is to be
discovered. The gay flutterer, so tender in its frame, must not be born
amid the snows of winter, or in the ungenial days of early spring; its
pupa, therefore, requires the warm influences of July and August before
it will undergo its change. If it were born earlier than that time it
would unquestionably perish, and the insect would become extinct; if
later, the same result would take place, for it would fall into the
killing power of the early winter evenings. As it is, all is well.
The insect and the day are made for one another; for it the flower
blossoms, and the warm air breathes, and all nature is spread out in
warmth and happiness. Its career run through, it departs from the scene
it has enlivened, leaving behind, just at the proper time, and in the
proper place, the eggs which are to become quickened, live, and die,
like itself, all in their appointed time. We thus perceive that it is
chiefly the increasing temperature of the air which fixes the time of
the insect's duration as a pupa, and sets in movement all the great
chain of the events of external nature. In what way an increase of
warmth thus acts we are still unable to say; perhaps, indeed, we may
never be able to tell. Neither can we understand how it should be, that
the principle of life should be ready at a moment's notice to complete
its work in the perfection of the insect, and yet held in abeyance
by a few degrees of a lower, or quickened into activity by a few
degrees higher, temperature. We know that this has been God's doing,
and marvellous it is in our eyes; but the wisest of men feels himself
ignorant if asked the question, how it is thus arranged? Truly none
but a God infinite in wisdom as well as love would take such thought
for so humble a creature as a poor insect; but let us not forget that
----"each crawling insect holds a rank
Important in the plan of Him who framed
This scale of beings,--holds a rank, which, lost,
Would break the chain, and leave behind a gap
Which Nature's self would rue."
The duration of the insect in the pupa state, though variable, is,
without doubt, limited, and sometimes it is fixed to _an hour_, quite
irrespective of all external circumstances. The most remarkable
example of this kind occurs in the case of the insects whose larva we
have already mentioned--the _Ephemera_. These insects appear with the
greatest regularity, issuing from the waters of the Seine or Marne, in
France, between the 10th and 15th of August. The fishermen call them
_manna_; and when their season is come, they say, "the _manna_ begins
to appear," or "the manna fell abundantly last night," alluding, by
this expression, either to the astonishing quantity of food which the
insects afford to the fish, or to the large quantity of fish which they
then take. The fishermen expect them with the greatest confidence
during these few days, nor are they ever disappointed. Millions upon
millions suddenly rise into the air between eight and ten o'clock
in the evening, and this generally for three successive nights.[N]
Whatever be the temperature of the atmosphere, whether it be cold or
hot, these flies invariably appear at the same hour in the evening,
that is, between a quarter and half-past eight; towards nine they begin
to fill the air; in the following half hour they are in the greatest
numbers; and at ten there are scarcely any to be seen. So that in
less than two hours--and these always the same--this infinite host of
insects leave their pupa state, become perfect insects, perform their
appointed work, and vanish. The same phenomenon of regularity of limit
to the pupa state occurs also in other insects, though, perhaps, less
strikingly. Some insects constantly leave the pupa at break of day;
others in the full tide of noon-day, and others when the shadows of
declining day come over the landscape. These, however, are certainly
exceptions to the general rule, which appears to lay down no precise
period of the day or month when this state is ended, and the perfect
state is entered upon; but a limit, nevertheless, exists, mainly
dependent for its appointment upon the external influences of warmth
and air.