staff of life:" yet should divine Providence in anger be pleased to
give the rein to the various insects which, in the different stages
of its growth, attack the plant producing it, how quickly would
this staff be broken! From the moment that _wheat_ begins to emerge
from the soil, to the time when it is carried into the barn, it is
exposed to their ravages. One of its earliest assailants in this
country is that of which Mr. Walford has given an account in the
_Linnean Transactions_, taking it for the wire-worm; but, as Mr.
Marsham observed, not correctly; it being probably the larva of
some coleopterous insect, perhaps of one of the numerous tribe of
_Brachyptera_ or rove-beetles which are not universally carnivorous.
This animal was discovered to infest the wheat in its earliest stage
of growth after vegetation had commenced; and there was reason to
believe that it began even with the grain itself. It eats into the
young plant about an inch below the surface, devouring the central
part; and thus, vegetation being stopped, it dies. Out of fifty acres
sown with this grain in 1802, ten had been destroyed by the grub in
question so early as October[270].--Other predaceous _Coleoptera_
will also attack young corn. This is done by the larva of _Zabrus
gibbus_, particularly with respect to wheat. In the spring of 1813
not less than twelve German hides (_Hufen_), equal to two hundred and
thirty English acres, were destroyed by it in the canton of Seeburg,
near Halle in Germany; and Germar (who with other members of the
Society of Natural History, at that place, ascertained the fact,)
suspects that it was the same insect, described by Cooti, an Italian
author, which caused great destruction in Upper Italy in 1776.--Not
only is the larva, which probably lives in that state three years,
thus injurious; but, what one would not have expected, the perfect
beetle itself attacks the grain when in the ear, clambering up the
stems at night in vast numbers to get at it.--Along with the larvæ
of this insect were found, in the proportion of about one fourth,
those of another beetle (_Melolontha ruficornis_), which seemed to
contribute to the mischief[271].
Mr. Markwick has given us the history of a fly that attacks wheat
in a later period of its growth, which, if it be not indeed the
same, appears to be nearly related to the _Musca Pumilionis_ of
Bierkander[272], (_Oscinis_ F.) accused by him of being extremely
injurious to rye in the spring. Our insect was discovered on the
first sown wheats early in that season, making its lodgement in the
very heart of the principal stem just above the root, which stem it
invariably destroyed, giving the crop at first a most unpromising
appearance, so that there seemed scarcely a hope of any produce.
But it proved in this and other instances that year (1791) that
the plant, instead of being injured, derived great benefit from
this circumstance; for, the main stem perishing, the root (which
was not hurt) threw out fresh shoots on every side, so as to yield
a more abundant crop than in other fields where the insect had
not been busy. These flies therefore seem to belong to our insect
benefactors; and I should not have introduced them here, had it not
been probable that in some instances later in the spring they may
attack the lateral shoots of the wheat, and so be injurious. It
is also not unlikely that the new progeny, which is disclosed in
May, may oviposit in barley or some other spring corn, which would
bring the next generation out in time for the wheat sown in the
autumn.--These flies are amongst the last, and, in some seasons, the
most numerous, that take shelter in the windows of our apartments
when the first frosts indicate the approach of winter, previous to
their becoming torpid during that season. When this little animal
was first observed in England, it created no small alarm amongst
agriculturists lest it should prove to be the _Hessian fly_, so
notorious for its depredations in North America; but Mr. Marsham, by
tracing out the species, proved the alarm to be unfounded[273]. That
there was sufficient cause for apprehension should it have so turned
out, what I have formerly stated concerning the latter insect, and
the additional facts which I shall now adduce, will amply show.
The ravages of the animal just alluded to, which was first noticed in
1776, and received its name from an erroneous idea that it was carried
by the Hessian troops in their straw from Germany, were at one time so
universal as to threaten, where it appeared, the total abolition of the
culture of wheat; though, by recent accounts, the injury which it now
occasions is much less than at first. It commences its depredations
in autumn, as soon as the plant begins to appear above ground, when
it devours the leaf and stem with equal voracity until stopped by the
frost. When the return of spring brings a milder temperature the fly
appears again, and deposits its eggs in the heart of the main stems,
which it perforates and so weakens, that when the ear begins to grow
heavy, and is about to go into the milky state, they break down and
perish. All the crops, as far as it extended its flight, fell before
this ravager. It first showed itself in Long Island, from whence it
proceeded inland at about the rate of fifteen or twenty miles annually,
and by the year 1789 had reached 200 miles from its original station.
I must observe, however, that some accounts state its progress at first
to have been very slow, at the rate only of seven miles per annum, and
the damage inconsiderable; and that the wheat crops were not materially
injured by it before the year 1788. Though these insect hordes traverse
such a tract of country in the course of the year, their flights are
not more than five or six feet at a time. Nothing intercepts them in
their destructive career, neither mountains nor the broadest rivers.
They were seen to cross the Delaware like a cloud. The numbers of this
fly were so great, that in wheat-harvest the houses swarmed with them
to the extreme annoyance of the inhabitants. They filled every plate or
vessel that was in use; and five hundred were counted in a single glass
tumbler exposed to them a few minutes with a little beer in it[274].
America suffers also in its wheat and maize from the attack of an
insect of a different order; which, for what reason I know not, is
called the chintz-bug-fly. It appears to be apterous, and is said
in scent and colour to resemble the bed-bug. They travel in immense
columns from field to field, like locusts destroying every thing as
they proceed: but their injuries are confined to the states south
of the 40th degree of north latitude[275]. From this account the
depredator here noticed should belong to the tribe of _Geocorisæ_,
Latr.; but it seems very difficult to conceive how an insect that lives
by suction, and has no mandibles, could destroy these plants so totally.
When the wheat blossoms, another marauder, to which Mr. Marsham first
called the attention of the public, takes its turn to make an attack
upon it, under the form of an orange-coloured gnat, which introducing
its long retractile ovipositor into the centre of the corolla, there
deposits its eggs. These being hatched, the larvæ, perhaps by eating
the pollen, prevent the impregnation of the grain, and so in some
seasons destroy the twentieth part of the crop[276].
One would think, when laid up in the barn or in the granary, that
wheat would be secure from injury; but even there the weevil
(_Calandra granaria_), in its imago as well as in its larva state,
devours it; and sometimes this pest becomes so infinitely numerous,
that a sensible man, engaged in the brewing trade, once told me,
speaking perhaps rather hyperbolically, that they collected and
destroyed them by bushels; and no wonder, for a single pair of these
destroyers may produce in one year above 6000 descendants.--There
are three other insects that attack the stored wheat, which are more
injurious to it than even the weevil. One is a minute species of moth
(_Tinea granella_), happily not much if at all known in this country;
of which Leeuwenhoek has given us a full history under the name of
the wolf. Another is a species of the same genus, at present not
named, which, as we are informed by Du Hamel, at one time committed
dreadful ravages in the province of Angoumois in France. The third is
_Trogosita caraboides_, a kind of beetle, the grub of which called
_Cadelle_, Olivier tells us, did more damage to the housed grain
in the southern provinces of France than either the weevil or the
wolf[277].--Here I may just mention a few other insects which devour
grains that are the food of man, concerning which I have collected
no other facts. The rice-weevil (_Calandra Oryzæ_) is very injurious
to the useful grain after which it is named, as is likewise another
small beetle, _Lyctus dentatus_, F. (_Sylvanus_, Latr.): and an
Indian grain called in the country _Joharré_, which appears to be
a species of Holcus or Milium, is the appropriate food of another
species of Calandra[278], which I found abundant in it.
_Rye_, in this island, is an article of less importance than wheat;
but in some parts of the continent it forms a principal portion of
the bread-corn. Providence has also appointed the insect means of
causing a scarcity of this species of food. The fly before noticed
(_Oscinis Pumilionis_) introduces its eggs into the heart of the
shoots of rye, and occasions so many to perish, that from eight
to fourteen are lost in a square of two feet.--A small moth also
(_Margaritia Secalis_) which eats the culm of this plant within the
vagina, thus destroys many ears[279]. In common with wheat and barley
it also suffers from Leeuwenhoek's wolf and the weevil.
_Barley_ likewise, another of our most valuable grains, has several
insect foes. The gelatinous larva of a saw-fly (_Tenthredo_, L.)
preys upon the upper surface of the leaves, and so occasions them
to wither. _Musca Hordei_ of Bierkander also assails the plant. A
tenth part of the produce of this grain, Linné affirms, is annually
destroyed in Sweden by another fly, not yet discovered in Britain,
(_Oscinis Frit_,) which does the mischief by getting into the ear,
as does likewise _O. lineata_, F.--A small species of moth described
by Reaumur, though not named by Linné, which may be called _Tinea
Hordei_, (_Ypsolophus granellus?_) devours the grain when laid up in
the granary. This fly deposits several eggs, perhaps twenty or thirty,
on a single grain; but as one grain only is to be the portion of one
larva, they disperse when hatched, each selecting one for itself, which
it enters from without at a place more tender than the rest;--and this
single grain furnishes a sufficient supply of food to support the
caterpillar till it is ready to assume the pupa. Concealed within this
contracted habitation, the little animal does nothing that may betray
it to the watchful eye of man, not even ejecting its excrements from
its habitation; so that there may be millions within a heap of corn,
where you would not suspect there was one[280].
I have not observed that _oats_ suffer from insects, except from
the universal subterranean destroyer of the grasses, the wire-worm,
of which I shall give you a more full account hereafter; and
occasionally from an Aphis. The only important grain that now remains
unnoticed is the _maize_ or Indian corn. Besides the chintz-bug-fly,
a little beetle[281] (_Phaleria cornuta_) appears to devour it; and
it has probably other unrecorded enemies. The Guinea corn of America
(_Holcus bicolor_), as well as other kinds of grain, is, according
to Abbott, often much injured by the larva of a moth (_Noctua
frugiperda_, Smith), which feeds upon the main shoot[282].
Next to grain _pulse_ is useful to us both when cultivated in our
gardens and in our fields. Peas and beans, which form so material
a part of the produce of the farm, are exposed to the attack of a
numerous host of insect depredators; indeed the former, on account
of their ravages, is one of the most uncertain of our crops. The
animals from which in this country both these plants suffer most are
the _Aphides_, commonly called leaf-lice, but which properly should
be denominated plant-lice.--As almost every animal has its peculiar
_louse_, so has almost every plant its peculiar _plant-louse_; and,
next to locusts, these are the greatest enemies of the vegetable
world, and like them are sometimes so numerous as to darken the
air[283]. The multiplication of these little creatures is infinite
and almost incredible. Providence has endued them with privileges
promoting fecundity, which no other insects possess: at one time
of the year they are viviparous, at another oviparous; and, what
is most remarkable and without parallel, the sexual intercourse of
one original pair serves for all the generations which proceed from
the female for a whole succeeding year. Reaumur has proved that in
five generations one Aphis may be the progenitor of 5,904,900,000
descendants; and it is supposed that in one year there may be twenty
generations[284]. This astonishing fecundity exceeds that of any
known animal; and we cannot wonder that a creature so prolific
should be proportionably injurious; some species, however, seem
more so than others. Those that attack wheat, oats, and barley, of
which there are more kinds than one, seldom multiply so fast as
to be very noxious to those plants; while those which attack pulse
spread so rapidly, and take such entire possession, that the crop
is greatly injured, and sometimes destroyed by them. This was the
case with respect to peas in the year 1810, when the produce was
not much more than the seed sown; and many farmers turned their
swine into their pea-fields, not thinking them worth harvesting.
The damage in this instance was caused solely by the Aphis, and was
universal throughout the kingdom, so that a sufficient supply for the
navy could not be obtained. The earlier peas are sown, the better
chance they stand of escaping, at least in part, the effects of this
vegetable Phthiriasis.--Beans are also often great sufferers from
another species of plant-louse, in some districts from its black
colour called the _Collier_, which begins at the top of the plant,
and so keeps multiplying downwards. The best remedy in this case,
which also tends to set the beans well, and improves both their
quality and quantity, is to top them as soon as the Aphides begin to
appear, and carrying away the tops to burn or bury them.--In a late
stage of growth great havoc is often made in peas by the grub of a
small beetle (_Bruchus granarius_), which will sometimes lay an egg
in every pea of a pod, and thus destroy it.--Something similar I
have been told (I suspect it is a short-snouted weevil) occasionally
injures beans. In this country, however, the mischief caused by the
Bruchus is seldom very serious; but in North America another species
(_B. Pisi_) is most alarmingly destructive, its ravages being at one
time so universal as to put an end in some places to the cultivation
of that favourite pulse. No wonder then that Kalm should have been
thrown into such a trepidation upon discovering some of these
pestilent insects just disclosed in a parcel of peas he had brought
from that country, lest he should be the instrument of introducing so
fatal an evil into his beloved Sweden[285]. In the year 1780 an alarm
was spread in some parts of France, that people had been poisoned
by eating worm-eaten peas; and they were forbidden by authority to
be exposed for sale in the market: but the fears of the public were
soon removed by the examination of some scientific men, who found the
cause of the injury to be the insect of which I am now speaking[286].
Another species of Bruchus (_B. pectinicornis_) devours the peas in
China and Barbary. A leguminous seed, much used when boiled as food
for horses in India, known to Europeans by the name of _Gram_, but
in the Tamul dialect called _Koloo_, and by the Moors _Cooltee_, is
the appropriate food of a fourth kind of Bruchus, related to the
last, but having the antennæ, which in the male are pectinated, much
shorter than the body. It is, perhaps, _B. scutellaris_. A parcel of
this seed[287] given me by Captain Green was full of this insect,
several grains containing two. Molina, in his History of Chili, tells
us of a beetle, which he names _Lucanus Pilmus_, that infests the
beans in that country;--a circumstance quite at variance with the
habits of the _Lucanidæ_, which all prey upon timber. This insect was
probably a _Phaleria_, in which genus the mandibles are protruded
from the head like those of _Lucanus_; and one species, as we have
seen above, feeds upon maize.
Great profits are sometimes derived by farmers from their crops
of _clover-seed_: but this does not happen very often; for a small
weevil, (_Apion flavifemoratum_,) which abounds every where at almost
all times of the year, feeds upon the seed of the purple clover, and
in most seasons does the crop considerable damage; so that a plant of
the fairest appearance will, in consequence of the voracity of this
little enemy, produce scarcely any thing. Another species (_Apion
flavipes_) infests the Dutch or white clover[288]. The young plants
of purple clover, when just sprung, are often, as Mr. Joseph Stickney
pointed out to me, much injured by the same little jumping beetles
(_Haltica_) that attack the turnips.
But not only, if let loose to the work of destruction, might insects
annihilate our grain and pulse; they would also deprive the earth of
that beautiful green carpet which now covers it, and is so agreeable
and so refreshing to the sight. When you see a large tract of land
lying fallow, as is sometimes the case in open districts, with no
intervening patches of verdure, how unpleasant and uncomfortable is
it to your eye! What then would be your sensations, were the whole
face of the earth bare, and not dressed by Flora? But such a state
of things would soon take place, if to punish us, or to teach us
thankfulness to the great Arbiter of our fate, the insects that
feed upon the _grass_ of our pastures were to become as generally
numerous as they are occasionally permitted to do. One of the worst
of these ravagers is the grub of the common cock-chafer (_Melolontha
vulgaris_.)[289] This insect, which is found to remain in the
_larva_ state four years, sometimes destroys whole acres of grass,
as I can aver from my own observation. It undermines the richest
meadows, and so loosens the turf that it will roll up as if cut with
a turfing-spade. These grubs did so much injury about seventy years
ago to a poor farmer near Norwich, that the court of that city,
out of compassion, allowed him 25_l._, and the man and his servant
declared that he had gathered eighty bushels of the beetle[290].
In the year 1785 many provinces of France were so ravaged by them,
that a premium was offered by the government for the best mode of
destroying them. They do not confine themselves to grass, but eat
also the roots of corn; and it is to feast upon this grub more
particularly that the rooks follow the plough.
The larva also of another species of a cognate genus (_Hoplia
pulverulenta_) is extremely destructive in moist meadows, rooting
under the herbage, so that, the soil becoming loose, the grass soon
withers and dies. Swine are very fond of these grubs, and will devour
vast numbers of them, and the rooks lend their assistance.
Amongst the _Lepidoptera_, the greatest enemy of our pastures is the
_Charæas Graminis_, which, however, is said not to touch the foxtail
grass. In the years 1740, 1741, 1742, 1748, 1749, they multiplied
so prodigiously and committed such ravages in many provinces of
Sweden, that the meadows became quite white and dry as if a fire had
passed over them[291]. This destructive insect, though found in this
country, is luckily scarce amongst us; but our northern neighbours
appear occasionally to have suffered greatly from it. In 1759, and
again in 1802, the high sheep farms in Tweedale were dreadfully
infested by a caterpillar, which was probably the larva of this moth;
spots of a mile square were totally covered by them, and the grass
devoured to the root[292].
Most of the insects I have hitherto mentioned attack our crops
partially, confining themselves to one or two kinds only; but there
are some species which extend their ravages indifferently to _all_.
Of this description is the _Pyralis? frumentalis_, which moth, Pallas
tells us, is an almost universal pest in the government of Kasan
in Russia, often eating the greater part of the spring corn to the
root[293]. To this we are fortunately strangers; but another, well
known by the name of the wire-worm, causes annually a large diminution
of the produce of our fields, destroying indiscriminately wheat, rye,
oats, and grass[294]. This insect, which has its name apparently from
its slender form, and uncommon hardness and toughness, is the grub of
one of the elastic beetles termed by Linné _Elater lineatus_, but by
Bierkander, to whom we are indebted for its history, _E. Segetis_[295],
which name is now generally adopted. The late ingenious Mr. Paul of
Starston in Norfolk, (well known as the inventor of a machine[296]
to entrap the turnip-beetle, which may be applied by collectors with
great advantage to general purposes,) has also succeeded in tracing
this insect from the larva to the imago state. His grubs produced
_Elater obscurus_ of Mr. Marsham, which however comes so near to _E.
Segetis_ that it is doubtful whether it be more than a variety. The
other species, however, of the genus have similar grubs, many of which
probably contribute to the mischief. When told that it lives in its
first (or feeding) state not less than five years, during the greatest
part of which time it is supported by devouring the roots of grain, you
will not wonder that its ravages should be so extensive, and that whole
crops should sometimes be cut off by it. As it abounds chiefly in newly
broken-up land, though the roots of the grasses supply it with food, it
probably does not do any great injury to our meadows and pastures[297].
Here also may be included the larva of the long-legged gnat (_Tipula
oleracea_), known in many parts by the name of _the grub_, which
is sometimes very prejudicial to the grass in marshy lands, and at
others not less so to corn. Reaumur informs us, that in Poitou, in
certain years, the grass of whole districts has been so destroyed by
it, as not to produce the food necessary for the sustenance of the
cattle[298]. In many parts of England, in Holderness particularly, it
cuts off a large proportion of the wheat crops, especially if sown upon
clover-lays[299]. Reaumur concludes from the observations he made that
it lives solely upon earth, and consequently that the injury which it
occasions, arises from its loosening the roots of corn and grass by
burrowing amongst them: but my friend Mr. Stickney, the intelligent
author of a treatise upon this insect, is inclined to think from his
experiments that it feeds on the roots themselves. However this may be,
the evil produced is evident; and it appears too from the observations
of the gentleman last mentioned, that this animal is not killed by lime
applied in much larger doses than usual[300].
Our national beverage ale, so valuable and heartening to the lower
orders, and so infinitely preferable to ardent spirits and tea,
is indebted to another vegetable, the _hop_, for its agreeable
conservative bitter. This plant so precious has numberless enemies
in the Lilliputian world to which I am introducing you. Its roots
are subject to the attack of the caterpillar of a singular species
of moth (_Hepiolus Humuli_), known to collectors by the name of the
ghost, that sometimes does them considerable injury[301].--A small
beetle also (_Haltica concinna_) is particularly destructive to the
tender shoots early in the year; and upon the presence or absence of
Aphides, known by the name of _the fly_, as in the case of peas, the
crop of every year depends; so that the hop-grower is wholly at the
mercy of insects. They are the barometer that indicates the rise and
fall of his wealth.