to keep the animals of their own class within their proper limits;
and I cannot doubt that you will recognise the goodness of the Great
Parent in providing such an army of counterchecks to the natural
tendency of almost all insects to incalculable increase. But before
I quit this subject I must call your attention to what may be
denominated _cannibal insects_, since in spite of those declaimers
who would persuade us that man is the only animal that preys upon his
own species[503], a large number of insects are guilty of the same
offence. Reaumur tells us, that having put into a glass vessel twenty
caterpillars of the same species, which he was careful to supply
with their appropriate food, they nevertheless devoured each other
until one only survived[504]; and De Geer relates several similar
instances[505]. The younger larvæ of _Calosoma Sycophanta_ often
take advantage of the helpless inactivity into which the gluttony of
their maturer comrades has thrown them, and from mere wantonness it
should seem, when in no need of other food, pierce and devour them. A
ferocity not less savage exists amongst the _Mantes_. These insects
have their fore legs of a construction not unlike that of a sabre;
and they can as dexterously cleave their antagonist in two, or cut
off his head at a stroke, as the most expert hussar. In this way
they often treat each other, even the sexes fighting with the most
savage animosity. Rösel endeavoured to rear several specimens of _M.
religiosa_, but always failed, the stronger constantly devouring
the weaker[506]. This ferocious propensity the Chinese children
have, according to Mr. Barrow, employed as a source of barbarous
amusement, selling to their comrades bamboo cages containing each a
_Mantis_, which are put together to fight. You will think it singular
that both in Europe and Africa these cruel insects have obtained a
character for gentleness of disposition, and even sanctity. This
has arisen from the upright or sitting position, with the fore legs
bent, assumed in watching for their prey, which the vulgar have
supposed to be a praying posture, and hence adopted the belief that a
child or traveller that had lost his road would be guided by taking
one of these pious insects in his hands and observing what way it
pointed. _Mantis fausta_, though not as some suppose worshiped by
the Hottentots, is yet greatly esteemed by them, and they regard
the person upon whom it alights as highly fortunate[507]. A similar
unnatural ferocity is exhibited by _Gryllus campestris_, of which
having put the sexes into a box, I found on examining them that the
female had begun to make her meal off her companion.--The malign
aspect of the scorpion leads us to expect from it unnatural cruelty,
and its manners fulfill this expectation. Maupertuis put a hundred
scorpions together, and a general and murderous battle immediately
began. Almost all were massacred in the space of a few days without
distinction of age or sex, and devoured by the survivors. He informs
us also that they often devour their own offspring as soon as they
are born[508]. Spiders are equally ferocious in their habits,
fighting sanguinary battles, which sometimes end in the death of
both combatants; and the females do not yield to the Mantes in their
unnatural cruelty to their mates. Woe be to the male spider that
after an union does not with all speed make his escape from the
fangs of his partner! Nay, De Geer saw one that, in the midst of his
preparatory caresses, was seized by the object of his attentions,
enveloped by her in a web, and then devoured--a sight which, he
observes, filled him with horror and indignation[509].
* * * * *
Such are the benefits which we derive from the insects that keep each
other in check. Here they are the _destroyers_ to which we are chiefly
indebted: but we are in another point of view under nearly equal
obligations to the _destroyed_; for they are insects, either wholly or
in part, that form the food of some of our most esteemed fishes, and
of birds that are not more valuable to us as articles for the table,
than as the songsters that enliven our groves. But before proceeding
to the details which this view of the subject involves, I ought not to
omit pointing out to you that many quadrupeds, which though not all of
direct utility to us are doubtless of importance in the scale of being,
derive a considerable part of their subsistence from insects.
The harmless hedgehog and the mole, to begin at the lower end of the
series, are both said to be insectivorous[510]; the latter devouring
large quantities of the wire-worms. The greedy swine will root up
whole acres in search of the grubs of cockchafers, of which they are
very fond; and perhaps the good they do is greater than the harm,
if their attack be confined to grass that having been undermined
by these grubs would soon die: they also dig up the larvæ of the
destructive _Cicada septendecim_, called the American locust[511], on
which, when in their perfect state, the squirrels are said to grow
fat[512]. The badger, Lesser informs us, will eat beetles: and its
kinsman the bear has the character of being very fond of ants and of
honey; which last is also said to be a favourite article with the
fox, who has sometimes the audacity to overturn bee-hives, and even
to attack wasps' nests in search of it. He will also eat beetles.
Sparrman has given an amusing account of the honey-ratel, (_Viverra
mellivora_,) which has a particular instinct enabling it to discover
bees, and attack them in their entrenchments. Near sun-set the
ratel will sit and hold one of his paws before his eyes, in order
to get a distinct view of the object of his pursuit; and when, in
consequence of his peering about in this manner, he sees any bees
flying, he knows that at this time of the day they are making for
their habitations, whither he follows them, and so attains his
end[513]. Another species of Viverra (_V. prehensilis_) is also
reputed to be an eager insect-hunter. The young armadillos feed on a
species of locust; but no quadruped can with more propriety be called
insectivorous than the ant-eaters (_Myrmecophaga_), which, as their
name imports, live upon ants. The great ant-eater, when he comes to
an ant-hill, scratches it up with his long claws, and then unfolds
his slender worm-like tongue, (which is more than two feet long, and
wet with saliva,) and when covered with ants draws it back into his
mouth and swallows thousands of them alive, renewing the operation
till no more are to be found. He also climbs trees in search of
wood-lice and wild-honey. Bats, as every one knows, are always
flitting about in summer evenings, hawking for insects: and the Lemur
and monkeys will also eat them.
Insects likewise afford a favourite kind of food to many reptiles:
the tortoise; frogs and toads; and lizards too of different kinds.
St. Pierre mentions a small and very handsome species in the island
of Mauritius, that pursues them into the houses, climbs up the walls,
and even walks over glass, watching with great patience for an
opportunity of catching them[514]. The common snake also is said to
receive part of its nutriment from them.
But to revert to insects as indirectly advantageous to us, by
furnishing food to fishes and birds, beginning with the former.
Our rivers abound with _fish_ of various kinds, which at particular
seasons derive a principal part of their food from insects, as the
numerous species of the salmon and carp genus. These chiefly prey
upon the various kinds of _Trichoptera_, in their larva state called
case- or caddis-worms, and in their imago may-flies (though this last
denomination properly belongs only to the _Sialis lutaria_, which
generally appears in that month,) and _Ephemeræ_. Besides these, the
waters swarm with insects of every order, as numerous in proportion
to the space they inhabit, as those that fill the air, which form the
sole nutriment of multitudes of our fish, and the partial support of
almost all.
Reaumur has given us a very entertaining account of the infinite
hosts of Ephemeræ that by myriads of millions emerge at a certain
season of the year from some of the rivers in France, which, as it is
well worth your attention, I shall abridge for you.
These insects in their first and intermediate state are aquatic:
they either live in holes in the banks of rivers or brooks below the
water, so that it enters into their habitations, which they seldom
quit; or they swim about and walk upon the bed of the stream, or
conceal themselves under stones or upon pieces of stick. Though their
life, when they assume the perfect state, is usually extremely short,
some being disclosed after sun-set, laying their eggs and dying
before sun-rise; and many not living more than three hours; yet in
their preparatory state their existence is much longer, in some one,
in others two, in others even three years.
The different species assume the imago at different times of the
year; but the same species appear regularly at nearly the same
period annually, and for a certain number of days fill the air in
the neighbourhood of the rivers, emerging also from the water at
a certain hour of the day. Those which Swammerdam observed, began
to fly about six o'clock in the evening, or about two hours before
sun-set; but the great body of those noticed by Reaumur did not
appear till after that time; so that the season of different harvests
is not better known to the farmer, than that in which the Ephemeræ
of a particular river are to emerge, is to the fishermen. Yet a
greater degree of heat or cold, the rise or fall of the water, and
other circumstances we are not aware of, may accelerate or retard
their appearance. Between the 10th and 15th of August is the time
when those of the Seine and Marne, which Reaumur described, are
expected by the fishermen, who call them _manna_: and when their
season is come, they say "the manna begins to appear, the manna fell
abundantly such a night;"--alluding, by this expression, either to
the astonishing quantity of food which the Ephemeræ afford the fish,
or to the large quantity of fish which they then take.
Reaumur first observed these insects in the year 1738, when they did
not begin to show themselves in numbers till the 18th of August. On
the 19th, having received notice from his fisherman that the flies had
appeared, he got into his boat about three hours before sun-set, and
detached from the banks of the river several masses of earth filled
with pupæ, which he put into a large tub full of water. This tub,
after staying in the boat till about eight o'clock, without seeing any
remarkable number of the flies, and being threatened with a storm, he
caused to be landed and placed in his garden, at the foot of which
ran the Marne. Before the people had landed it, an astonishing number
of Ephemeræ emerged from it. Every piece of earth that was above the
surface of the water was covered by them, some beginning to quit their
slough, others prepared to fly, and others already on the wing; and
every where under the water they were to be seen in a greater or less
degree of forwardness. The storm coming on, he was obliged to quit the
amusing scene; but when the rain ceased to fall he returned to it. As
soon as the cloth with which he had ordered the tub to be covered was
removed, the number of flies appeared to be greatly augmented, and kept
continually increasing: many flew away, but more were drowned. Those
already transformed, and continually transforming, would have been
sufficient of themselves to have made the tub seem full; but their
number was soon very much enlarged by others attracted by the light. To
prevent their being drowned, he caused the tub to be again covered with
the cloth, and over it he held the light, which was soon concealed by a
layer of these flies, that might have been taken by handfulls from the
candlestick.
But the scene round the tub was nothing to be compared with the
wonderful spectacle exhibited on the banks of the river. The
exclamations of his gardener drew the illustrious naturalist thither:
and such a sight he had never witnessed, and could scarcely find
words to describe. "The myriads of Ephemeræ," says he, "which filled
the air over the current of the river, and over the bank on which I
stood, are neither to be expressed nor conceived. When the snow falls
with the largest flakes, and with the least interval between them,
the air is not so full of them as that which surrounded us was of
Ephemeræ. Scarcely had I remained in one place a few minutes, when
the step on which I stood was quite concealed with a layer of them
from two to four inches in depth. Near the lowest step a surface
of water of five or six feet dimensions every way was entirely
and thickly covered by them: and what the current carried off was
continually replaced. Many times I was obliged to abandon my station,
not being able to bear the shower of Ephemeræ, which, falling with
an obliquity less constant than that of an ordinary shower, struck
continually, and in a manner extremely uncomfortable, every part of
my face:--eyes, mouth and nostrils were filled with them." To hold
the flambeau on this occasion was no pleasant office. The person who
filled it had his clothes covered in a few moments with these flies,
which came from all parts to overwhelm him.--Before ten o'clock this
interesting spectacle had vanished. It was renewed for some nights
afterwards, but the flies were never in such prodigious numbers. The
fishermen allow only three successive days for the great fall of the
manna: but a few flies appear both before and after, their number
increasing in one case, in the other diminishing. 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 this infinite host of flies emerge from their parent stream,
fill the air, perform their appointed work, and vanish. A very large
proportion of them falls into the river, when the fish have their
grand festival and the fishermen a good harvest[515].
Under this head I may observe how much the patient angler is
indebted to insects for some of his choicest baits, for the best
opportunities of showing his skill, and for the most gratifying part
of his diversion. The case-worm and several other larvæ are the best
standing bait for many fish. The larva of the Ephemera, there called
bait and bank-bait[516], is much used in some parts of Holland. The
case-worms, and grubs (I suppose of flies) from the tallow-chandlers
are in request with us for roach and dace; and I am told by an acute
observer of these things, the Rev. R. Sheppard, that the _Geotrupes_
and _Melolonthæ_ are good baits for chub[517]. But to be an adept
in fly-fishing, which requires the most skill and furnishes the
best diversion, the angler ought to be conversant in Entomology,
at least sufficiently so to distinguish the different species of
_Phryganea_ and other _Trichoptera_, and to know the time of their
appearance.--The angler is not only indebted to insects for some of
his best baits, but also for the best material to fasten his hooks
to, and even for making his lines for smaller fish--the Indian grass
or gut as it is called, (termed in France _Cheveux de Florence_,)
which is said to be prepared in China from the matter contained in
the silk reservoirs of the silk-worm, but according to Latreille is
the silk vessel itself when dried[518].
* * * * *
One of the most important ends for which insects were gifted with
such powers of multiplication, giving birth to myriads of myriads of
individuals, was to furnish the feathered part of the creation with
a sufficient supply of food. The number of birds that derive the
whole or a principal part of their subsistence from insects is, as is
universally known, very great, and includes species of almost every
order.
Amongst the _Accipitres_ the kestril (_Falco Tinnunculus_, L.)
devours abundance of insects. A friend of mine, upon opening one
found its stomach full of the remains of grasshoppers and beetles,
particularly the former, which he suspects constitute great part of
the food of this species. One of the shrikes, also, or butcher-birds
(_Lanius Collurio_)--and it is probable that other species of this
numerous genus may have the same habits--is known to feed upon
insects, which it first impales alive on the thorns of the sloe and
other spinous plants, and then devours. If meat be given it, when
kept in a cage, it will fix it upon the wires before it eats it.
_Lanius Excubitor_ also impales insects, but Heckewelder denies that
it feeds upon them. If he be correct, the object of this singular
procedure with that species, may be to allure the birds, which it
preys upon, to a particular spot[519].
Amongst the _Picæ_ or Pies the _Crotophaga_, called the Ani, which
is a native of Africa and America, lives upon the locust and _Ixodes
Ricinus_, which it picks in great numbers from the backs of cattle;
but none are greater devourers of insects in this order than rooks.
It is for the grubs of _Melolontha_, _Tipula_, &c., that they follow
the plough; and they always frequent the meadows in which these
larvæ abound, destroying them in vast numbers. Kalm tells us, that
when the little crow was extirpated from Virginia at an enormous
expense, the inhabitants would willingly have brought them back
again at double the price[520]. The icteric oriole is kept by the
Americans in their houses for the sake of clearing them of insects;
and the purple grackle is so useful in this respect, that when, on
account of their consuming grain, the American farmers in New England
offered a reward of threepence a head for them, and they were in
consequence nearly extirpated, insects increased to such a degree
as to cause a total loss of the herbage, and the inhabitants were
obliged to obtain hay for their cattle not only from Pennsylvania but
even from Great Britain[521]. Of this order also is the bee-cuckoo
(_Cuculus Indicator_) so celebrated for its instinct, by which
it serves as a guide to the wild bees' nests in Africa. Sparrman
describes this bird, which is somewhat larger than a common sparrow,
as giving this information in a singular manner. In the evening
and morning, which are its meal-times, it excites the attention of
the Hottentots, colonists, and honey-ratel, by the cry of _cherr,
cherr, cherr_, and conducts them to the tree or spot in which the
bees' nest is concealed, continually repeating this cry. When
arrived at the spot, it hovers over it, and then alighting on some
neighbouring tree or bush, sits in silence, expecting to come in for
its share of the spoil, which is that part of the comb containing
the brood[522].--The wryneck and the woodpeckers, the nut-hatch and
tree-creeper, live entirely upon insects and their eggs[523], which
they pick out of decayed trees and out of the bark of living ones.
The former also frequents grass-plats and ant-hills, into which
it darts its long flexible tongue and so draws out its prey. The
woodpecker likewise draws insects out of their holes by means of the
same organ, which for this purpose is bony at the end and barbed,
and furnished with a curious apparatus of muscles to enable them to
throw it forwards with great force. Some species spit the insects on
their tongue, and thus bring them into their mouth. In America, the
tree-creeper is furnished with a box at the end of a long pole to
entice it to build in gardens, which it is found to be particularly
useful in clearing from noxious insects.
Amongst the _Grallæ_ or Waders, many of the long-billed birds eat the
larvæ of insects as well as worms: and they form also no inconsiderable
part of the food of our domestic poultry, especially turkeys, which
may be daily seen busily engaged in hunting for them, and, as well as
ducks, will greedily devour the larger insects, as cockchafers, and
in North America _Cicadæ_. Mr. Sheppard was much amused one day in
July last year with observing a cow which had taken refuge in a pond,
probably from the gad-fly, and was standing nearly up to its belly in
water. A fleet of ducks surrounded it, which kept continually jumping
at the flies that alighted upon it. The cow, as if sensible of the
service they were rendering her, stood perfectly still though assailed
and pecked on all sides by them. The partridge takes her young brood to
an ant-hill, where they feast upon the larvæ and pupæ, which Swammerdam
informs us were sold at market in his time to feed various kinds of
birds[524]. Dr. Clarke also mentions having seen them, as well as the
ants themselves, exposed to sale in the market at Moscow as a food for
nightingales[525]. Latreille tells us that singing birds are fed in
France with the larvæ of the horse-ant (_Formica rufa_).
But the Linnean order of _Passeres_ affords the greatest number of
insectivorous birds; indeed almost all the species of this order,
except perhaps the pigeon-tribe, and the cross-bill and other Loxiæ,
more or less eat insects. Amongst the thrush tribe, the blackbird,
though he will have his share of our gooseberries and currants, assists
greatly in clearing our gardens of caterpillars; and the locust-eating
thrush is still more useful in the countries subject to that dreadful
pest: these birds never appear but with the locusts, and then accompany
them in astonishing numbers, preying upon them in their larva state.
The common sparrow, though proscribed as a most mischievous bird,
destroys a vast number of insects. Bradley has calculated that a single
pair having young to maintain, will destroy 3360 caterpillars in a
week[526]. They also prey upon butterflies and other winged insects.
The fly-catchers (_Muscicapa_) and the warblers (_Motacilla_), which
include our sweetest songsters, are almost entirely supported by
insects; so that were it not for these despised creatures we should
be deprived of some of our greatest pleasures, and half the interest
and delight of our vernal walks would be done away. Our groves would
no longer be vocal; our little domestic favourites the red-breast and
the wren would desert us; and the heavens would be depopulated.--We
should lose too some of the most esteemed dainties of our tables, one
of which, the wheat-ear, is said to be attracted to our downs by a
particular insect[527]. Lastly, insects are the sole food of swallows,
which are always on the wing hawking for them, and their flight is
regulated by that of their prey. When the atmosphere is dry and clear
and their small game flies high, they seek the skies; when moist and
the insects are low or upon the ground, they descend and just skim
the surface of the earth and waters; and thus by their flight are
regarded as prognosticating fair or wet weather. I was last summer
much interested and amused by observing the tender care and assiduity
with which an old swallow supplied her young with this kind of food.
My attention was called to a young brood, that having left their nest
before they were strong enough to take wing, were stationed on the lead
which covers a bow window in my house. The mother was perpetually going
and returning, putting an insect into the mouth first of one and then
of the others in succession, all fluttering and opening their mouths
to receive her gift. She was scarcely ever more than a minute away,
and continued her excursions as long as we had time to observe her.
When the little ones were satisfied, they put their head under their
wing and went to sleep. The number of insects caught by this tribe is
inconceivable. But it is not in summer only that birds derive their
food from the insect tribes: even in winter the pupæ of _Lepidoptera_,
as Mr. White tells us, are the grand support of those that have a soft
bill[528].
* * * * *
I shall close my list of the indirect benefits derived from insects,
by adverting to the very singular apparent subserviency of some of
them to the functions of certain vegetables.
You well know that some plants are gifted with the faculty of catching
flies. These vegetable Muscicapæ, which have been enumerated by Dr.
Barton of Philadelphia, who has published an ingenious paper on the
subject[529], may be divided into three classes: First, those that
entrap insects by the irritability of their stamina, which close upon
them when touched. Under this head come _Apocynum androsæmifolium_,
_Asclepias syriaca_ and _curassavica_, _Nerium Oleander_, and a grass
described by Michaux under the name of _Leersia lenticularis_. The
second class includes those which entrap them by some viscosity of
the plant, as many species of _Rhododendron_, _Kalmia_, _Robinia_,
_Silene_, _Lythrum_, _Populus balsamifera_, &c.[530] And under the
third class will arrange those which ensnare by their leaves, whether
from some irritability in them, as in _Dionæa_, _Drosera_, &c., or
merely from their forming hollow vessels containing water, into which
the flies are enticed either by their carrion-like odour, or the sweet
fluid which many of them secrete near the faux, as in _Sarracenia_,
_Nepenthes_, _Aquarium_, _Cephalotus_, &c., the tubular leaves of which
are usually found stored with putrefying insects. In this last class
may be placed the common _Dipsacus_ of this country, the connate leaves
of which form a kind of basin round the stem, that retains rain-water
in which many insects are drowned. To these a fourth class might be
added, consisting of those plants whose flowers smelling like carrion
(_Stapelia hirsuta_, &c.) entice flies to lay their eggs upon them,
which thus perish.
The number of insects thus destroyed is prodigious. It is scarcely
possible to find a flower of the _Muscicapæ Asclepiadeæ_ that has not
entrapped its victim, and some of them in the United States closely
cover hundreds of acres together.