HABITS OF THE LARVA.
Generally, for a little while after the larva has emerged from the
shell, it is in a very weak and languid condition. The effort of
extricating itself from its little prison-house, seems to leave it
almost without strength; and for a period which varies in different
insects, it lies helpless and almost motionless at the mercy of any
wandering adversary, and might be demolished without resistance. But
this hour of weakness, except in a few cases, is not prolonged. In
the course of an hour or two, or even much less in some instances,
the larva revives, takes heart, and begins by eating whatever food
may happen to lie in its way; and now the larva becomes a terror to
the world of insects, or even, indirectly, to man and to nations.
Instead of simply eating, in order to live, like most other beings,
it only lives to eat; it has no other duty to perform at present but
to eat as fast and as much as it possibly can in a certain time; and
it must be confessed, the larva, generally speaking, leaves little to
be desired on the score of a sharp appetite. Unlike other creatures
who allow themselves a certain period between their meals, the larva
sets to its feast and does not leave the table until it has devoured
all its contents,--upon which it immediately begins again elsewhere.
No _gourmand_ in the world, whether among human beings or brutes, can
compare with the insect in this form for the amount of food consumed.
Morning, noon, and night, is to it only a continued round of feasting;
and, as may well be imagined, the larva grows very rapidly accordingly.
Some larvæ consume animal, others vegetable food; or, in the language
of science, some are _carnivorous_, some are _graminivorous_ or
_herbivorous_, and some will eat anything almost that comes before
them--these would be called, and very appropriately so, _omnivorous_.
Let us speak of carnivorous larvæ first. The larvæ which have
carnivorous propensities render themselves often truly terrible to the
insect world around them. The most mighty warrior that ever lived in
his whole career never slew half so many of his own species as the
larva of a beautiful fly does of _aphides_ in a few hours. Well does
Réaumur call them the "lions of the aphides," and thus does he describe
their method of proceeding:--
[Illustration: _Lion of the Aphides._]
"There is no beast of prey in nature who hunts so entirely at his ease
as does this larva. Resting upon a twig or a leaf, he is surrounded on
every side by the insects on which he feeds; often, indeed, they touch
his sides, and he is able to catch hundreds of them without changing
his position. Not only do the poor little aphides not fly from him, but
they may be often seen creeping over the body of their enemy. It is
only after the larva has eaten up the greater number of his prey around
him, that he has any need to remove to a spot as thickly inhabited by
them as that in which he has been making his cruel ravages. In order to
observe the manner in which he attacks them, the best plan is to take
him, put him between two leaves, and shut him up in a box for ten or
twelve hours to sharpen his appetite. After this fast he must be placed
on some spot where the aphides are found in abundance. Immediately he
begins exploring around for prey, which he does simply by the sense of
touch, as he does not appear to be able to see. At length an unhappy
insect comes within his reach. Brandishing a trident with which he
is armed, he immediately transfixes the insect, just as we take up a
morsel of food upon a fork!" The little creature is then sucked into
a sort of cavity like the neck of a bottle, where it is retained by a
couple of pins until its juices are emptied by the destroyer, when he
casts it away, now nothing more of it being left but a dry, shrivelled,
empty skin. The aphis-lion, however, loses no time, and presently
seizes another, which he pierces and sucks dry as quickly as the
last.[D] When very hungry he will devour one a minute. Réaumur says, "I
have seen him eat twenty of these insects one after another in twenty
minutes; nor did this satisfy him: for in the course of two hours he
devoured more than a hundred insects with which I supplied him!" These
larvæ do repose a little, but never for long, for they are seldom
without some prey in hand. "I have seen," adds the last author, "twigs
of the elder seven or eight inches in length entirely covered with
these insects, (the _aphides_,) and in four days' time there remained
not one alive."
This larva is a rare specimen of courage, as well as of destructive
powers; for when it is quite young it often seizes upon an insect
twice as big as itself. It is very amusing to see the unequal contest
between the little but courageous foe, and his great, bulky, and stupid
adversary. Immediately the larva thrusts its trident into the body of
the enemy, who, stupid as he is, does not like the sensation of the
wound in his side, and makes off as fast as he can. The lion-hearted
larva follows him up and wrestles with him, and at length actually
boards him, to use a sailor's term, clambering up his sides, and, in
triumph, piercing him through and slaying him. What is perhaps most
singular of all, the larvæ of some species of these flies not only
slay their victims, but actually clothe themselves, after the manner of
Hercules on his victory over the Nemæan lion, with the skins of their
prey!
It is almost to be regretted that the insect world has not had the
privilege of having its combats sung by the poets. Who can forget the
animated scenes, painted in such life-like colours by Homer and Virgil,
of the conflicts, hand to hand, of the heroes of their verse? But the
history of insects supplies us with more singular and more interesting
deeds of fight than have ever yet been fabled by poets, or commemorated
in song. In the instance we are about to quote, the larva of the
ant-lion is the crafty Giant Grim, who lives by entrapping, as we have
before said, poor wayfaring travellers. Like those giants of old, of
whom we read in books a little more wonderful than true, this subtle
and powerful enemy lies deeply ensconced in his subterraneous cavern,
patiently abiding the time when his unsuspecting prey shall fall into
his power. His trap is depicted on the opposite page.
[Illustration: _An Ant-lion in its Trap._]
This insect is naturally a very helpless being, it can only walk at
a slow pace, and strange to add, it can only walk backwards, and not
forwards! Yet its food is the juice of insect bodies. How, then, is
it to seize upon them circumstanced so unfavourably as it is, having
neither swiftness nor ability to direct its motions sufficiently
actively to fit it for such a task? It succeeds by an artifice of the
most refined character. Nothing daunted by what we might call its
natural disadvantages, the insect sets bravely to work to construct a
trap for its prey; and the manner in which this is performed may well
strike us with wonder, and raise our admiration up to Him who has so
marvellously endowed this humble being with wisdom and skill. It first
takes care to choose out a proper site for the work it is about, and
in this always selects a soil composed of fine, loose, and dry sand,
well aware that, as we shall presently see, no other would be fit for
its purpose. Generally it chooses such a soil under the shelter of an
old wall, where the rain cannot easily penetrate and ruin its work. In
so doing it shows its wisdom; for thither, when the heat of the sun is
great, or when the rain-drops fall heavily, crowds of insects come for
shelter, and fall into its cruel embrace.
[Illustration: _Circular Ditch of the Ant-lion._]
The site being chosen, the next important step is to mark out the
bounds of its habitation, and with this view the insect begins digging
a circular ditch, walking backwards until it has completed the circle.
This defines the outer limits of its trap, and is a sort of guide line
to it in its future operations. Then it sets about the more proper task
of excavating its trap. Would that our readers could see this insect at
work! Of all the wonderful sights presented to us in the insect world
there is none to equal it in interest, none so calculated to enlist our
sympathies on the part of the patient, skilful, and unwearied little
labourers of this kingdom of nature. Guided by the line it has marked
out, the workman steps into the circle, and sets to work with a hearty
good will, and with a degree of diligence and excavating skill that
would put our railroad "navigators" to the blush. Shower after shower
of sand is seen flying up and beyond the boundary described, with the
most unintermitting diligence, until the insect has completed the
circle again; arrived there, it turns round and excavates back again
until it arrives at the same point. But it may perhaps be asked, where
are its tools, and by what means does it succeed in casting up these
loads of earth? We fear that at best any written description will
hardly do justice to our ingenious labourer; its method, however, is as
follows:--It uses the head as the spade, or rather shovel, and in the
strangest manner it fills the shovel with one of its feet with a load
of sand, and then by a quick movement of the head tosses it out of the
cavity. By working in alternate directions it manages so as never to
over-fatigue one leg, for on its return the leg previously in use is
at rest, while the one on the opposite side is now called into duty.
The insect thus works on until its trap is completely excavated, the
task occupying a variable time; sometimes being finished in half an
hour, sometimes even in less, but occasionally occupying several hours,
the little labourer being obliged to rest a certain time. Réaumur, who
has given a fascinating account of these insects, writes, "I have had
at times hundreds of ant-lions in a large box, and I have often been
amused with filling up their traps. Some of them would immediately
begin to form another; but the greater number in the warm long days of
summer deferred executing the work until the sun began to go down. They
seldom worked in the heat of the day; but in cold or cloudy weather
they would excavate at any hour."
We well know what perplexity a chain of rocky hills causes to a
railroad engineer, and what vast outlays of money, labour, and time
are necessary in order to overcome the obstacle thus presented to
the path of the engine and its train. But it may be safely said that
we can furnish a parallel instance of difficulty and of patient,
all-surmounting exertion from the history of the insect before us. M.
Bonnet was curious to know what it would do if a stone or some such
obstacle were met with in the process of its excavations, and one day
had the gratification of observing the behaviour of the insect under
these trying circumstances. Not being able to cast it out with its
head, the insect determined to carry it out, if possible, on its back.
With this view it contrived by various manoeuvres to place the stone
upon its back and to balance it there. This was the least difficult
part of the undertaking. The insect had to climb up an inclined plane
upon soil, chosen with other views purposely by itself, as shifting and
unsteady as possible, and not only so, but to preserve the balance of
the stone with which it was encumbered. Undaunted by these difficulties
it made the attempt, but the first step brought down a shower of sand,
and tumbled the little rock to the bottom. Again and again did the
heroic insect attempt the same feat, and with the same ill success, and
we might have thought we beheld a realization of the fable of Sisyphus
and the rolling-stone, in the vain endeavours of the insect to get
rid of its encumbrance. Five or six times did the insect repeat its
endeavours, and at last, after one or two narrow escapes, the stone was
fairly lodged on the outside of the trap, and the insect returned to
its subterraneous recess at the bottom of the cell in triumph.
The traps vary in size in proportion to the age of the insects which
construct them. The young insects only form very small ones; but as
even from the moment of their birth they are destined to toil for their
food, they do not wait in idleness and hunger because they cannot make
large efforts, but are content to make little traps not more than a few
parts of an inch in diameter. Thus they set us the needful example of
not despising to do small things because our strength is not yet equal
to the performance of as much as we could desire. The diameter of the
trap formed by a full-grown insect is about three inches; the depth
about two.
When its labours are over, it has been well remarked, the insect
now only requires patience--but it must have a good deal of it! It
generally buries itself, all but its jaws, in the sand at the bottom,
and here awaits its victims. If it requires much patience, surely it
also needs to have much power of endurance of hunger, for it may wait
for days sometimes without catching any prey. Frequently, when this is
the case, it marches out of its trap, and tries its fortune in some
more favourable spot. But see! an ant who has been out foraging for the
young ants at home is hastening back laden with sweet treasures, when
suddenly she finds her path arrested by what appears to her to be a
deep but smooth precipice. To plunge down and rise on the opposite side
is a shorter cut, in her estimation, than to go round; or perhaps she
is led by curiosity to wish to explore this singular cavity, and she
plants her feet on its treacherous edge, causing a few grains of sand
to roll down and give notice to the wary giant below that a victim is
at hand. A step back, and her life would be saved; but no, she leaves
the bank, trusts herself to the unfaithful soil of the sides of the
precipice, and instantly rolls down in a cloud of dust to the bottom.
Terror has now laid hold of her, and with all speed she strives to
clamber up the unsteady sides. For a moment escape appears possible,
but the Argus-eyed monster below starts up into activity, and piling
upon his head a huge load of sand, he shoots it after the escaping ant,
and once more brings her down covered with dust into his embrace. The
terrible jaws are instantly closed upon the unhappy insect, and in a
few minutes her existence is at an end, the savage enemy shaking her
violently, or dashing her quivering frame against the earth.
Singular to add, the ant-lion loves not dead prey, and will indignantly
cast it out of its trap. Says Réaumur, "They appear so much to delight
in the glory of a victory, that they disdain to touch an insect who
is not, to say the least, in a condition to contend with them!" It
certainly is not that the food when offered to it dead is not fresh
enough that it is thus treated; for if only killed an instant before
the insect still refuses to touch it. Réaumur is disposed to believe
that, like our sportsmen, these interesting but cruel insects destroy
prey more for the pleasure of exhibiting their superior skill, than
to appease their hunger. But it is rather uncharitable even to the
ant-lion, to say so much as this. When the insect has sucked all the
juices out of its victim's body, it casts it out of its trap, and the
earth around, strewed with dead bodies, is thus the silent witness to
the destroying powers of the giant within.
This singular insect, whose exploits have detained us so long, remains
in its larva form two years, growing daily in size until it has
completed its existence as a larva, and must then enter upon another
condition of life. It is to be regretted that it is not to be found in
England, or at least it has not been for some time discovered in our
island; but it is common in France and other parts of the continent,
and would well repay the trouble of being brought over. As the insect
is very patient of hunger, it might easily be conveyed in a little
wooden box, half filled with fine sand, and its proceedings could be
readily watched by placing it under a bell-glass, or in a little glass
case, introducing a few ants or spiders for its food from time to time.
The insect exhibits to us a wonderful instance of what we may call,
after the example of Dr. Paley, the principle of compensation in
nature. It can neither run nor fly with the speed necessary to overtake
its prey who are swifter of foot than itself. But God never created
it to starve, and has endowed it with a rare combination of faculties
by which it is enabled to live in the midst of plenty if not even of
luxuriance. So it is in a thousand other cases in nature. So it is
indeed in Providence likewise. If He sends us trials, "He also makes
a way to escape that we may be able to bear them." If our day is to
be dark and cloudy, and to call for the exercise of much faith and
patience, there is still the same provision made; "as thy day so shall
thy strength be." If our lot in life is one of hardship He can, and if
it is sought of him aright He will, and He does bear us up, revive our
drooping strength, and enable us to go on our way rejoicing.
[Illustration: _Cells of Sand-Wasp._]
Let us go on to speak now of some other carnivorous larva. If in the
month of July we can find out a spot where we can detect the traces of
the labours of the sand-wasp, of whom mention has been made at page
15, and cutting out a little mass of the sand-rock containing several
of their burrows, then take the trouble to open gently one of the
cells formed by these insects, we shall see a carnivorous larva in as
happy a condition as a fox in a hen-roost, or a mouse in the midst
of a cheese! The best way to obtain access to this securely imbedded
and luxurious larva, is to moisten the mass of sand with a little
water, and then slice it gently down with an old knife until we come
to the cells. They are here represented. At the bottom of each we
shall see the larvæ which have sprung from the eggs deposited in the
manner before described, after the arduous and affectionate labours of
the parent. Then above each is a heap of caterpillars, arranged with
beautiful neatness, and larvæ and caterpillars are both fast locked
in their prison house by the firm stopping with which the parent wasp
has closed the mouth of the cells. These caterpillars are all alive,
and are rolled into a ring-like form, but are so chained down that
they cannot move in the least degree. The poor prisoners, like the
sheep in the slaughter-yard, are only waiting their turn to be killed
and devoured. The larva soon after it is hatched finds himself in the
midst of a well-stored larder, and has nothing to do but eat, which he
does not long delay doing. He devours at his ease, and revels in the
dainty fresh food which the care of his parent had laid up. When he has
eaten all his prisoners up, and grown to his full size, he lays down to
sleep, to awake again in another and a far different form.
[Illustration: _Larva of Wood-boring Wasps._]
Sometimes the reader may have the opportunity, it may be, of finding
out the nest of the wood-boring wasp, and he may in June or July,
perhaps, succeed in discovering another instance of a larva in a happy
state of plenty. The larva is sure to be found at the bottom, and above
it will be piled a heap of insects for its food. What is remarkable
about this store of food is, that the insects thus made prisoners are
not dead, for they would, if so, soon become corrupted, and unfit for
the diet of the larva; they are in a sort of half stupified condition,
in all probability very like that induced by the late plan of breathing
ether and other vapours to render persons insensible to pain, while
surgically operated on. Since this plan has been introduced, we read
in some of the newspapers--we may question with what truth--that the
butchers in Albany (America,) give ether to the oxen before killing
them, so as to make them insensible to the pain of the death-blow! But
the wasps in question have for ages been in the habit of effecting the
same end by stinging their captives, the poison not sufficing to kill
them, nor yet permitting them to be actively alive.
The insects thus stored up for the larva cost the parent many a
conflict in their capture. And here we may interest the reader by
describing the exploits of a warrior wasp, abundant in the Isle of
France. It is curious that in the Isle of France the common bee is not
to be found as a native of the woods, while, in the Isle of Bourbon, it
is very common, and furnishes an abundance of wax and honey. This is
explained by supposing that the warriors of whom we are about to speak
destroy the bees, and have thus prevented their multiplying in the
island in question. Truly, like the banditti of whom we read in books,
these wasps are splendidly attired, although not in the spoils of those
they have robbed. Their head, chest, and body is of a resplendent
lustre; now green, or, seen in another position, blue, and glistening
with all the lustre of an exquisite varnish; their antennæ are black,
their eyes of a brownish yellow, and their legs partly bronze-coloured,
and partly of a beautiful violet. They are strong and swift of wing,
and are possessed of a terrible lance, the thrusts of which even man
cannot endure without far more pain and inflammation than attends an
ordinary sting.
The foe with whom these magnificently-dressed warriors have to contend,
is a kind of insect allied to the cockroach, which, in our kitchens,
has acquired the incorrect title of "black beetle." This insect is
detested by the inhabitants of the island, for its ravages upon almost
everything of value or delicacy, and is not less hated by the sailor
for its destructiveness on ship-board. It is called _Kakerlac_, and
is much larger than the cockroaches, which are the plague and terror
of our cooks. Imagine that one of these great and odious insects is
marching along the highway. The warrior wasp has also been making
his expeditions for prey abroad, when suddenly his eager eye catches
sight of the kakerlac hastening to some new scene of depredation. The
warrior instantly alights, and the kakerlac stops, thinking perhaps to
intimidate its adversary by its size and ferocious aspect. Both insects
glare at one another;--
----"each other from afar
They view, and rushing on, begin the war.
They launch their spears; then hand to hand they meet,
The trembling soil resounds beneath their feet;
Their bucklers clash, thick blows descend from high,
And flashes of fire from their hard helmets fly.
Courage conspires with chance, and both engage
With equal fortune yet, and mutual rage."
Virgil's description, though scarcely accurate in all points, gives us
a lively image of this insect combat. The kakerlac, however, is the
Turnus, and the warrior wasp the Æneas of the fight. The wasp is the
first to attack, and darts upon the other, seizing it by the muzzle
with its strong jaws, then bending its body so as to bring its tail
under the abdomen of the kakerlac, the lance with its charge of poison
is deep-plunged into the body of the unhappy foe, imbuing a deadly
venom into its system. Having made this thrust, the warrior looses the
foe, and soars in triumph a little way into the air, satisfied of a
successful issue.
The wretched kakerlac, after a few brief convulsions, lies paralysed
on the ground unable to stir a step from the spot where it encountered
its terrible adversary. Fully aware of this, the victorious wasp,
after taking a few turns, as if to proclaim the downfall of the Giant
Kakerlac to the surrounding neighbourhood, returns to the scene where
the conflict was fought. The kakerlac, unable to resist the victor,
and being naturally, though a great devourer, a very faint-hearted
creature, lies immovable while the wasp seizes the prostrate foe by the
head, and in a sort of triumphal march drags it along the road to its
nest. But though the kakerlac was not a difficult enemy to overcome,
the weight and size of its body are a sore burden to the victor wasp.
The way to the nest is long, tedious, and rugged. After a hard pull
over all sorts of obstacles the wasp becomes completely breathless,
and is obliged to let go, and for a rest it generally rises into the
air, probably with a view of reconnoitring future difficulties, and
of ascertaining the best route to pursue. Thus, after alternately
dragging along the body of its victim and rising up to spy out the
path, at length the conqueror succeeds in bringing the carcase home.
Here, however, arises another difficulty. To attempt to get the body
of the huge kakerlac in, is just as if one were to attempt to get an
elephant through a small street-door. What is to be done? The wasp
enters the hole backwards, and, seizing the head of the kakerlac,
endeavours with all its might to drag it in, but all in vain. Many
times it repeats these efforts with the same want of success; and now
it appears that its labours in bringing hither the corpse, and its
dangers in the battle, were all for nought, for the great body cannot
be put in the place the wasp had designed for it. As if exasperated
with the difficulties, out comes the wasp in fury, and falling upon
the body of the kakerlac, hews off the large wing-cases, together with
several of the limbs, and goes back into the hole again to repeat the
attempt to get it in. Success at length crowns its efforts; by little
and little the body becomes lost to sight, and finally disappears
altogether from view, being carried down to the very bottom of the
nest. Here the larva, as soon as hatched, feeds upon it, thrives, and
grows, and falls asleep, awaiting the time when itself shall awake to
follow in the steps of the glittering and formidable warrior who, with
the boldness of an amazon and affection of the tenderest of mothers,
supplied it with nourishment during its hours of infancy.
This may be thought a scene of sad carnage, but the following will,
perhaps, appear even more so. What should we say, if deep in the
forests of some wild uncultivated country was found a den, the bottom
of which was strewed with skulls, with bones, and mangled limbs? What
fearful scenes should we not suspect to have taken place in this dark
and horrid place; and as we shuddered in looking round upon its walls,
as the once witnesses of terrible deeds, we might even fancy we heard
the cry of the poor traveller, whose last agonies were seen by no eye
but that of the monster who had waylaid and murdered him? Such a den
may be found in the forest, made horrible by the cut-off heads, limbs,
and wings of insects--it is the habitation of the carnivorous larva
of a wasp. Nay more, as is seen in the engraving, the insect monster
actually works up the cut-off wings and limbs into a sort of covering
for itself, and finally buries itself in a shroud partly made of the
spoils of former victims.
[Illustration: _The Larva of a Wasp in its coat of wings and limbs._]
Perhaps the carnivorous larva of the tiger-beetle, or _cicindela_, is
as ferocious a being as any in this state. In this respect, indeed, it
resembles the perfect insect, whose title sufficiently indicates its
swiftness, cunning, and blood-thirsty nature. "These larvæ," writes Mr.
Westwood, "burrow cylindric retreats in the earth, to the depth of a
foot or more, employing their legs and jaws in loosening the particles
of sand and earth, which they carry to the surface upon their broad,
saucer-like head, ascending by the assistance of the two hooks upon the
back, somewhat after the fashion of a sweep going up a chimney! Having
completed this burrow, they station themselves, by means of their legs
and back hooks, at its mouth, their large flattened head and great
segment filling the hole." Here they remain all day long, and many an
insect might pass close by, little dreaming of the terrible foe who
lay under that trap-door. Presently comes a spider scrambling over
the ground in haste to mount up a branch on which to hang one of its
web lines; the treacherous trap-door is in its direct path. Its feet
rest on it; instantly the trap drops, and the poor insect falls into
the dark den, and is caught in the powerful jaws of the artful larva.
Truly, there is something even to man a little intimidating in the
sight of such a monster as is represented here; how much more to the
unfortunate insect who happens to be caught in its embrace, and having
only time to just catch a glimpse of its fearful captor, is dragged
down in a cloud of dust to be devoured in darkness at the bottom of
the den. Yet this also, like other cruel creatures, is in reality a
very timid larva, and instantly on the approach of danger, drops to
the bottom of the cell, where, if we have courage to pursue it, we
shall find it much in the attitude in which it is here represented. The
singular pair of hooks on its back are used as the flukes of an anchor
to sustain the insect in the position it assumes at the mouth of the
cell.
[Illustration: _Larva of the Tiger-Beetle._]
Mention has already been made in the previous chapter of the insects
called Ichneumons, which deposit their eggs in the bodies of the larvæ
of other insects. These, when hatched, are also to be reckoned among
the larvæ which prey upon flesh, since they devour the bodies of the
larvæ in which they have been deposited. They are thus most useful to
mankind in destroying the devourers of his vegetable food.
[Illustration: _Larva of the Dragon-fly._]
[Illustration: _The Mask partly open._]
[Illustration: _The same partly closed._]
We may now see an instance yet more strange of a carnivorous larva.
We must wend our way to the riverside in the months of May or June.
There, after a diligent search at the bottom, in some moderately
shallow portion of the stream shall we find a larva, the study of
which might well occupy us for many pages. Yet it is the larva of
an insect well known to every angler and brook-side wanderer--the
dragon-fly. This larva is provided with one of the most remarkable
contrivances for seizing its prey and conveying it to its mouth, of any
being in the zoological kingdom. By the assistance of the engraving,
we may perhaps be able to render this apparatus, which is somewhat
complicated, intelligible to the reader. Looking at the larva's head,
we are reminded somewhat of that of a horse who has got blinders over
his eyes, and a nose-bag over his nose, and partly up his cheeks.
Now suppose the two blinders thrown back on each side, then conceive
that the lower part of the face which we have supposed covered with a
nose-bag were to be uncovered, we should then see the following curious
contrivance. The lower lip of this larva is lengthened downwards into
a sort of _arm_, if we may so speak; at what we may call the _elbow_,
is a joint connecting the upper and lower portions of it, and the place
of the hand is occupied by two cross plates, with a claw at the end of
each. Suppose an unhappy insect, or even a tadpole, swims carelessly by
the larva, immediately the two sides of the mask, or blinders, as we
have called them, fly open; the arm is uncovered, the forearm let down,
and by means of the plates, which we have compared to the hand, the
victim is caught, and bending the arm back, is presented to the mouth
of the larva. There is much similarity in this organ with the wonderful
apparatus of the elephant called its trunk; but of the two, the trunk
of this insect is the most beautiful piece of animal mechanism. When
the prey has been devoured, the arm folds up, covers the mouth and part
of the face of the insect, and the blinders, or two side pieces of the
mask, fall in, and lock together in a toothed manner, as the engraving
in the last page shows.
[Illustration: _The apparatus in the act of seizing._]
Thus provided, the larva is a formidable creature to the inhabitants
of the pond or brook; few, indeed, more so. It preys with incessant
activity on all aquatic insects that happen to come in its way, and
sometimes, as we have said, even upon tadpoles. They do not even spare
one another, and woe to the unhappy relative of the family who happens
to wander near the abode of another of the same family, anxious to
begin his feasting for the day! So ferocious are they, that they
even attack small fish, and make little work of swallowing them up.
Not only are these creatures fierce, but they also possess all the
cunning of a tiger or a cat. To watch them seize their prey is an
interesting occupation, and as the larvæ are common enough, and may be
easily recognised by comparing them with the accompanying cut, we may
venture to recommend the amusement of observing their proceedings to
the reader. A little way off lies an unsuspecting insect delighting
in the warm sunshine, and securely floating upon the waters on the
corner of a leaf. Such an idea as danger at hand is probably the very
last from its conceptions, and pluming its bright and glossy wings, it
beguiles away the sunny hour unmolested by a passing enemy, or a breath
of air. The larva has marked it already for its own.[E] See it rouse
itself up, and noiselessly make ready to pounce upon the unsuspecting
lounger. It creeps stealthily along, concealing itself from view as far
as possible, and not even the tell-tale glassy surface of the water
feels its movements. Measuring its distance well, the larva prepares
to seize its prey; in a moment, swifter than the eye can follow, the
victim is caught by the apparatus we have described, and in another
instant, is in all the agonies of a violent death in the mouth of the
larva. So exceedingly cautious are these larvæ in their movements, and
so expert and active in darting upon their prey, that it scarcely ever
escapes their power.
[Illustration: _Cockchafer._]
[Illustration: _Larva._]
Having mentioned these particulars about carnivorous larvæ, let us
consider some circumstances connected with those larvæ that are
vegetable feeders--graminivorous or herbivorous. Of these, we could
scarcely select a more destructive one than the larva of an insect well
known to every school-boy from the times of Greece and Rome down to our
own--the common cockchafer, (_Melolontha vulgaris_.) Our schoolboys,
however, are less merciful than those of Greece, for _they_ only tied
a string round the leg of the unhappy cockchafer, while _these_
thrust a pin through its tail. Yet, its terrible ravages considered,
the insect little deserves to be pitied; but, we are not therefore
to be understood as by any means sanctioning the cruel and inhuman
sport alluded to. These larvæ are hatched in a sort of little cavern
dug by the parent insect's care under the ground in our meadows, or
corn-fields. Here they begin their ravages by devouring the roots of
the grasses which surround them on all sides. In this manner they very
quickly destroy the plants, which wither and die in a manner quite
mysterious to the agriculturist, if he does not happen to think of
these insects. The turf soon becomes so completely undermined by these
excavators, that it may be rolled off as smooth as if a knife had been
used underneath to cut off all its connexions with the ground. In a few
weeks, meadows which shone in all the fresh and luxuriant green raiment
of Spring, change colour, and before Summer has yet come, and before
the stalks of the grass are yet grown up, one would think Autumn had
passed over the face of the field, from its dry and dead aspect. About
seventy years ago, we are told these larvæ did so much injury to a poor
farmer's fields near Norwich, that the court of that city, out of
compassion, presented him with twenty-five pounds. Some idea of their
numbers on this farmer's property may be formed from the fact that the
farmer and his servant declared, with very long faces, we may be sure,
that they had gathered eighty bushels of them. Sometimes they even
attack the roots of young trees, and in this manner do an incalculable
amount of mischief to plantations. They were at one time so abundant in
France, and did such immense mischief, that the Government, in order
to get rid of them, offered a handsome reward for the best method of
destroying them. A number of experiments were made, and it really
seemed as if nothing would kill these larvæ, in the way of poison at
least, for several poisons which are rapidly fatal to man and animals
failed to produce the least effect on them. It was found, however,
at last, that a solution of alkalies, such as potash and soda, were
certain poisons to them, and should land be much infested with them, it
would be worth the trial to water it with such solutions, especially
as they tend rather to enrich the soil than otherwise. A French
manufacturer, determining to turn the visitation of these insects to
good account, has succeeded in distilling an excellent _lamp-oil_ from
their bodies, and offers tenpence a bushel for them. From seventeen
bushels he extracted twenty-eight quarts of good oil! In Hungary, a
kind of grease is obtained from them which is useful for carriage
wheels. The ingenuity of man may thus even procure good out of a very
formidable evil, although the mischief done by the cockchafer larva
undoubtedly far exceeds the benefit it confers upon its captors in the
amount of oil extracted from it.
An insect almost equally familiar to all persons is the long-legged
gnat, of whom the famous children's rhyme runs:--
"'Old father long-legs' would not say his prayers;
Take him by the left leg and throw him down stairs."
Many of our farmers would be glad, no doubt, if taking him by the left
leg would keep him out of their meadows, for there this insect commits
fearful ravages in the larva form. In some parts of England it has as
completely destroyed the pasture-grass as if it had been consumed by
fire. In the spring of 1813, hundreds of acres of pasture in the rich
district of _Sunk Island_ in Holderness were entirely destroyed by
it, being rendered as completely brown as if they had suffered a three
months' drought, and no other vegetation but that of a few thistles was
left on land, which, at more favoured periods, was more than commonly
luxuriant. On a square foot of the turf being dug up from the affected
spot, the enormous number of _two hundred and ten_ larvæ was counted
in it. Fortunately, the next year showed a very different result, for
then it was difficult on careful search to find one! In some districts
of France it is also very destructive, the grass of large tracts being
so completely destroyed by it, that enough food for the maintenance of
the cattle is not to be obtained. These larvæ, like the last-named,
appear to destroy by eating away the roots of the grass. From these and
the foregoing facts, entomology teaches us to regard these two insects,
upon which we commonly look with compassion, as occasionally becoming
the formidable, though indirect, enemies of man. The scientific name
for "Father Long-legs" is _Tipula oleracea_. The French call them
oddly enough milliners, or tailors, (_couturiéres, tailleurs_,) a
name of which it is harder to guess the origin than the common one
of father-long-legs, which is sufficiently expressive of one of the
features of the insect in the perfect state: perhaps the French tailors
are distinguished for being very long and thin!
[Illustration: _The Gamma Moth and Larva._]
We may yet linger awhile in the fields for another illustration of the
devouring propensities of vegetable-feeding larvæ. The pretty moth
represented in the accompanying engraving, together with its larva, was
once the cause of more alarm in France than we can readily conceive.
It is often to be seen in our meadows plunging its minute drinking
apparatus into the depths of the wild flowers, and flitting to and fro
at no great height from the ground all the day long, and even after
sun-down. It is called generally the Gamma moth, or _Plusia gamma_,
in consequence of the little mark in its wings, which resembles the
Greek letter [Greek: g]. Its larva is striped with green, and when
multiplied excessively, as was the case in France in the year 1735,
produces scenes of desolation which, as the results of apparently
an insignificant insect's doings, can scarcely be credited. In the
months of June and July in that year they became so numerous, that the
gardeners and peasantry in the districts plagued by them declared that
they must have been created by enchantment. In some places Réaumur
was assured that an old soldier had been seen to throw the spell. In
other places an ugly old woman, who was as wicked as she was frightful,
had caused all the mischief. Their prodigious numbers appeared to the
ignorant and superstitious peasantry an indubitable proof that they
were created by sorcery. And though we cannot, of course, sympathise
with their thoughts on this subject, we can well imagine and feel for
their astonishment and dismay as they beheld the wide desolation of
every green thing produced by the innumerable millions of these larvæ,
which covered forest, field and garden with their bodies. Many persons
began to fear they were really poisonous creatures, and refused in
consequence to partake of salads or other vegetable food of a similar
kind. This was probably an equal error with the last; and it is very
droll to find the talented Réaumur pleading with great earnestness that
the caterpillars were not unwholesome as food. He even declares his
opinion, that if these creatures were to become excessively numerous
in France, the inhabitants might be compelled to treat them as the
wretched inhabitants of Africa do the locusts, and when they have eaten
up every green thing, fall upon and eat _them_. With as much learning
and eloquence as if he was treating one of his most favourite topics in
entomology, M. Réaumur recommends these larvæ for human food, adding,
that a very little time would enable us to conquer our disgust at such
aliment, and that we should even welcome to our tables a dish of the
larvæ in question as an agreeable luxury! It is to be hoped, if ever
such a custom be originated, it will be confined to the place of its
birth--the country of this great, but, in this respect, whimsical
naturalist.
To account for their excessive multiplication, we have no need to have
recourse to enchantment for a solution of the difficulty. Each of the
gamma moths produces about four hundred eggs; now, if there were only
twenty larvæ in a certain locality which lived through the winter, and
became perfect insects in May following, the eggs deposited by these
would, supposing all to be hatched, produce, according to a calculation
made by Réaumur, in the course of a single year, _eight hundred
thousand_ larvæ. Well may we exclaim, then, with this learned author,
"Should we not rather wonder at the wisdom and forethought which has
ordered matters so that these insects increase to annoy us so rarely?"
The wonder is, in truth, not that they should multiply so excessively
at particular periods, so much as that it should be so seldom that they
are multiplied even to the extent of which they are naturally capable.
Thus, if we suppose that all the eggs of the moths of this species were
to be hatched, it is more than probable that a large portion of our
vegetation would be consumed by them. How is this guarded against? In
various ways. The eggs are not all capable of being hatched, or if so,
are not allowed to escape injury by various accidents, and the larvæ
themselves are a prey to countless enemies among the birds, while they
also frequently perish owing to the severity of winter. From these
considerations we may readily perceive how completely the well-being of
a great nation, with the lives of a large portion of its inhabitants,
are dependent upon the preserving, protecting, and restraining
influence of the providence of God. With the return of every year, we
may say, the question is asked by this tribe of insects alone, "Shall
we go forth to destroy and devour at once, or shall we refrain?" With
every year the silent reply is experienced by man in the unmolested
condition of his fields, gardens, and vineyards. "Oh!" we may ejaculate
with the Psalmist, "Oh that men would consider these things! then
should they understand the loving-kindness of the Lord."
[Illustration: _Destructive Larva and its Nest._]
Another and more remarkable instance of the destruction caused by
vegetable-eating larvæ may be quoted from the fertile pages of the
same illustrious naturalist, M. Réaumur, particularly because it is
the narration of one who was an eye-witness to the facts of which he
speaks. "In two journeys," he writes, "which I made from Paris to
Poitou, at the commencement of the month of September in 1730, and
also in 1731, I noticed that from Paris all the way to Tours every
oak, great and small, had been attacked by larvæ; the highest branches
appeared to be principally selected by them. Great isolated oak trees,
as well as those which formed dense forests, were alike attacked in
this manner, their summits being absolutely withered and dry. Had we
not known how greatly the larvæ may multiply, and what fearful ravages
they are capable of committing, one might have conceived that some hot
and blasting wind had reduced the leaves to this condition. In certain
districts, the hedges along the road-side had not a single leaf that
was not withered up." The engraving represents one of these mischievous
larvæ; it also shows the winter-nest into which they creep, and a leaf
which a regiment of them have already attacked.
Securely protected from the severity of the winter of 1731, in their
warm nests, these larvæ quitted them again early in April of 1732, to
set forth upon another mission of destruction. They had now multiplied
to a degree calculated to excite the most serious public alarm. It
began to be feared that the leaves of the trees would not be sufficient
for the support of the devouring millions; and that if, during that
year, the larvæ multiplied in the same proportion as in the preceding
year, a famine more terrible than any recorded in history as produced
by insect destroyers would be the result. These fears were in some
measure groundless, as, in all probability, so soon as the larvæ had
devoured all the leaves, they would rather have perished of hunger
than have attacked the grass and other plants. But the matter was
sufficiently serious as it was. The French parliament took the alarm,
and determined to resist the threatened invasion of these small but
formidable enemies. An edict was therefore issued, calling upon all
persons to assist in removing the larvæ from the trees, while they
were as yet not reinforced by the addition of countless millions
more. In orchards, gardens, and pleasure-grounds this became a far
from difficult duty, because it was easy to ascend the trees and to
remove the larvæ and their nests. But in dense forests, where the tall
trees waved high in the air, and where every branch and every twig was
loaded with larvæ, it was plainly impossible. Although, as we know,
acts of parliament are able to effect a great deal, these insects set
their powers at defiance, and little good was really accomplished.
Having thus, as it were, manifested to the nation how powerless were
their efforts to remove the plague, it pleased God to interfere by
his providence, and a succession of cold rains for three days in
May effectually stopped the progress of the destroyers, by utterly
annihilating them.
Réaumur's remarks well deserve extracting; he says:--"I had been hoping
much from the effect of these showers, and attentively watched what
would be the result. I saw day by day that among the little bands of
larvæ which were aggregated together in order to cover the twigs of
the trees with silk, or to despoil them of their leaves, there were
many whose bodies became flabby, elongated, and devoid of roundness.
These quickly perished. Every day the mortality became more serious
among them. In a short time the larvæ, which had previously swarmed
upon the trees, became so few, that before ten or twelve days had
passed by I could not find a single one, although I looked carefully
for them." It is remarkable enough, and sets forth strikingly the
short-sightedness and ingratitude of man, that these very showers,
which produced what no combined efforts of human power could or did
effect, were bitterly complained of as inappropriate to the season, at
the time when they were falling! These larvæ were hatched from eggs
deposited by a common species of moth.
Although England has been often mercifully spared while continental
countries have largely suffered by such visitations as we have last
described, we have not always come off unscathed. The larvæ of a moth
nearly allied to, if not the same as the last-mentioned, produced an
alarm in 1782 in our country, perhaps even more extensive than the
previous one in France. All sorts of strange and silly rumours were
spread abroad; some believing that the larvæ were the harbingers of
coming disease and death. Poor people were hired to cut off the webs
of these larvæ at the rate of one shilling a bushel, and they were
then burned under the inspection of the churchwardens and overseers.
In the parish of Clapham, we are told by an author who wrote upon the
history of this insect, _eighty bushels_ were collected in one day!
Prayers were offered up in some churches to deliver the country from
the apprehended approaching calamity.
We need not, however, dwell longer upon the vegetable-consuming larvæ
out of doors. Unfortunately we are acquainted with instances equally
formidable within our barns, store-houses, and larders. In vain does
man lay up the increase of his fields with care in granaries of the
best construction, and using all possible precautions against the
introduction of insect enemies. The weevil, called scientifically the
_Calandra granaria_, finds entrance, and in a short time makes its
presence felt in the vast destruction it produces. So soon as they are
discovered, they are collected with all expedition by the owners of the
stores and consigned to the flames for their misdeeds. Sometimes they
are collected thus by bushels, from which it may readily be conceived
what has been the amount of damage they have done.
There is a little moth whose larva is equally mischievous in
appropriating to its own use the food and property of man; its name
is the _Tinea hordei_. This fly, we are told, deposits perhaps twenty
or thirty eggs in a single grain; but as one grain only is to be the
portion of one larva, so soon as they are hatched they disperse by
mutual consent in a very amicable manner, and each selects its future
home, so that in a short time the whole family is comfortably lodged in
twenty or thirty distinct grains of corn. There, surrounded by food,
they live and thrive, eating up all the precious parts of the grain,
until nothing remains but the husk. They then fall asleep and enter
upon the further stages of insect development. No one could possibly
tell by the external appearance of the corn, that the least mischief
had taken place within, the fulness and general aspect of the grain
being the same; but on carefully examining it, a very minute hole may
be found in some spot or other;--it was here the enemy got in. We need
scarcely add, that for any purpose grain which has been thus attacked
is rendered perfectly useless.
Any one who has ever been on a long sea-voyage will find it easy to
supply us with another example of a vegetable-food devouring larva. The
hard substances commonly called captain's biscuits are the objects of
attack, together with flour, peas, and similar articles of food, and
the attacking insect is the larva of the meal-worm, the entomological
title of which is _Tenebrio molitor_. In vain does the ship's cook,
with all his art, prepare a soup composed of the richest ingredients,
and calculated, as one would think, to gratify the taste of the
greatest epicure. The larvæ have been beforehand with him; they have
attacked and become mixed with the flour or the peas; and when the soup
which has cost him so much pains is brought to table, not even the keen
appetite of seafaring people can reconcile them to it, for it is full
of the dead bodies of these larvæ. So likewise is the biscuit, and in
disgust the guests are compelled to confine their attention principally
to such articles of food as are unpalatable to their insect enemies.
We have but little experience, in our favoured land, of the more
extensive domestic destructions wrought by larvæ. But in hot countries
they become formidable, by reason of their numbers. In India,[F]
particularly during the rainy season, the interior of the houses swarms
with them; some climb the walls, some ascend the table, some feast
on the viands, and altogether, by their numbers and appearance, they
produce a degree of disgust and loathing at food, which cannot be
overcome for a long time by fresh residents. We may mention, before
concluding this part of our subject, that of those that do annoy us
domestically, some have appetites for very strange kinds of food, some
love wine, some vinegar, some butter and cheese; some revel in a pot
of preserves, some attack our meat, and one is mentioned by Réaumur as
delighting in _chocolate_!
If surprise be expressed that we have dwelt so long upon the eating
propensities of larvæ, let it be remembered that it was formerly said
at p. 94, that the principal duty of the larva, so long as it lived,
was _to eat_. It is born often only to eat as much as possible, and
to grow as large as possible within a given time; and in obedience to
this principle, we find larvæ with the sharpest of sharp appetites
embark in their career of existence, eating from their birth, all the
way along to their final change. It is therefore, obviously, a very
important part of the larva's history of which we have been speaking
for some pages past. Considering the fact to have been now brought into
sufficient prominence, we shall proceed to notice the rate at which
larvæ grow, and the actual quantities of food some of them devour. Let
us speak of the last first.
[Illustration: _Silk-worm Moth and her Eggs._]
Silk, as the youngest of our readers knows, is the production of a
little larva commonly called the silk-worm. Now, some years ago, the
calculation was made that in the United Kingdom alone was consumed,
every year, not less than five million pounds of raw silk. By means
of very accurate experiments, it has been ascertained that, in order
to procure one pound of raw silk, we must have twelve pounds of the
cocoons spun by these larvæ. In order to produce twelve pounds of
cocoons, one hundred and ninety-two pounds of mulberry-leaves must be
eaten up; or, which is the same thing, for every pound of raw silk,
we have to supply to the worms one hundred and ninety-two pounds of
leaves. We can now leave the calculation in the reader's hands; but we
may mention the sum total: it is, that for every year's consumption of
raw silk by our country, there is a certain consumption of _ninety-six
millions of pounds_ of mulberry-leaves; and as one hundred pounds of
leaves are calculated as the produce of one tree, it follows that nine
millions six hundred thousand mulberry trees must grow, in order to
supply food to the silk-worms necessary to furnish Great Britain with
silk for one year. Let us add, that this five million pounds of raw
silk is the production of the inconceivably great number of _eighteen
thousand million silk-worms_. The Count Dandolo, who has written an
excellent treatise on this subject, in Italian, made a number of
experiments upon the actual quantity of leaves devoured by the larvæ
hatched from an ounce weight of eggs; and he found that the quantity
of leaves consumed by them up to the completion of their development
as larvæ, amounted to upwards of sixteen hundred and nine pounds! In
a month from being first hatched, each larva consumes above an ounce
of leaves. As at first each larva only weighs the hundredth part of a
grain, it follows that it devours, in thirty days, about sixty thousand
times its original weight of leaves. If we suppose a puppy dog, just
born, to weigh a quarter of a pound, and to eat in the same proportion
for one month, it would have consumed, at the month's end, fifteen
thousand pounds of food. Could the puppy eat meat from the first,
which, as all are aware, he cannot, he would, at this rate, devour in
one month, from the time of his birth, one hundred and fifty sheep,
supposing each to weigh one hundred pounds; or about _five sheep_ for
his daily food! These calculations will show how voracious the larvæ
of the silk-worm are; and they are, probably, far from being among the
most voracious of the larvæ, only we are better acquainted with their
rate of devouring than with that of other insects in this state.
[Illustration: _Growth of Silk-worm Larvæ._]
All this eating cannot, of course, be unattended with a great increase
in the size of the larva. In some insects growth is prodigiously
rapid. A naturalist, who closely investigated this subject in the
common blow-fly, which is so apt to deposit its eggs upon meat in hot
weather, found that in the space of four-and-twenty hours, the larvæ
hatched from these eggs had increased to from one hundred and forty to
two hundred times their original weight. The larva of the great goat
moth, we are told by another, grows, altogether, to about seventy-two
thousand times its weight; but it takes three years so to do. In thus
growing, the larva becomes very fat and plump; and should it unhappily
cross the path of any bird, it would probably be nipped up as a dainty
morsel for the little ones in the distant nest. In birds, beasts, and
fishes, the rate of growth is much slower, and the amount of increase
much less. Fortunate is it for us that it is so; for what would become
of mankind if animals of the size of dogs could grow in a month to the
size of _elephants_, or young elephants to the size of _little hills_?
yet these comparisons are not exaggerated, remembering the increase and
growth of the silk-worm and of larvæ generally.