or
Elements of the Natural History of Insects
Volume 2
with plates
By William Kirby, M.A. F.R. and L.S.
Rector of Barham
and
William Spence, Esq. F.L.S.
Second Edition
Vol. II
London
Printed for Longman, Hurst, Rees, Ormi, and Brown,
Paternoster Row.
1818
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LETTER XXI.
MEANS BY WHICH INSECTS DEFEND THEMSELVES.
WHEN a country is particularly open to attack, or
surrounded by numerous enemies who from cupidity or hostile feelings are
disposed to annoy it, we are usually led to inquire what are its means
of defence? whether natural, or arising from the number, courage, or
skill of its inhabitants. The insect tribes constitute such a nation:
with them infinite hosts of enemies wage continual war, many of whom
derive the whole of their subsistence from them: and amongst their
own tribes there are numerous civil broils, the strong often preying
upon the weak, and the cunning upon the simple: so that unless a
watchful Providence (which cares for all its creatures, even the most
insignificant) had supplied them with some mode of resistance or escape,
this innnumerable race must soon be extirpated. That such is the case,
it shall be my endeavour in this letter to prove; in which I shall detail
to you some of the most remarkable rneans of defence with which they are
provided. For the sake of distinctness I shall consider these under two
separate heads, into which indeed they naturally divide themselves: -
Passive means of defence, such as are independent of any efforts of the
insect; and active means of defence, such as result from certain efforts
of the insect in the employment of those
instincts and instruments with which Providence has furnished it for this
purpose.
1. The principal passive means of defence with which insects are
provided, are derived from their colour and form, by which they either
deceive, dazzle, alarm, or annoy their enemies; or from their substance,
involuntary secretions, vitality, and numbers.
They often deceive them by various substances. Some times they
so exactly resemble the soil which they inhabit, that it must be a
practised eye which can distinguish them from it. Thus, one of our
scarcest British weevils
(Curculio nebulosus, L.),
by its gray colour spotted with black, so closely imitates the soil
consisting of white sand mixed with black earth, on which I have always
found it, that its chance of escape, even though it be hunted for by
the lyncean eye of an entomologist, is not small. Another insect of the
same tribe
(Brachyrhinus scabriculus, F.),
of which I have observed several species of common dors
(Harpalus, Latr.)
make great havoc, abounds in pits of a loamy soil of the same colour
precisely with itself; a circumstance that doubtless occasions many to
escape from their pitiless foes. - Several other weevils, for instance
Brachyrhinus niveus
and
cretaceus, F.,
resemble chalk, and perhaps inhabit a chalky or white soil.
Many insects also are like pebbles and stones, both rough and polished,
and of various colours; but since this resemblance sometimes results from
their attitudes; I shall enlarge upon it under my second head: whether,
however, it be merely passive, or combined with action, we may safely
regard it as given to enable them to elude the vigilance of their enemies.
A numerous host of our little animals escape from birds and other
assailants by imitating the colour of the plants, or parts of them,
which they inhabit; or the twigs of shrubs and trees; their foliage,
flowers, and fruit. Many of the mottled moths, which take their station
or diurnal repose on the north side of the trunks of trees, are with
difficulty distinguished from the gray and green lichens that cover
them. Of this kind are
Noctua aprilina
and
Psi, F.
The caterpillar of
N. Algæ, F.
when it feeds on the yellow
Lichen juniperinus,
is always yellow; but when upon the gray
Lichen saxatilis
its hue becomes graya
| a |
Fabr. Vorlesungen, 321. |
| b |
Cimic. Helvet. t. 172. f. 3. |
| c |
Hist. of Chili, i. 172. |
| d |
Since the first edition of this volume was
printed, a lady from the West Indies looking at my cabinet,
upon being shown this insect, exclaimed “Oh, that is The
Devil's Horse” |
This change is probably produced by the colour of its food.
Phryganea atra,
a kind of may-fly, frequents the black flower-spikes of the common sedge
(Carex riparia),
which fringes the banks of our rivers. I have often been unable to
distinguish it from them, and the birds probably often make the same
mistake and pass it by. - A jumping bug, very similar to one figured by
Schellenbergb, also much resembles the
lichens of the oak on which I took it.
The Spectre tribe (Phasma, Licht.) go still
further in this mimicry, representing a small branch with its spray. I
have one from Brazil eight inches long, that, unless it was seen to move,
could scarccly be conceived to be any thing else; the legs, as well as
the head, having their little snags and knobs, so that no imitation
can be more accurate. Perhaps this may be the species mentioned by
Molinac, which the natives of Chili call
“The Devil's Horsed.”
Other insects, of various tribes, represent the leaves of plants, living,
decaying, and dead; some in their colour, and some both in their colour
and shape. The caterpillar of a moth (Noctua
Ligustri, F.) that feeds upon the privet, is so exactly of the
colour of the underside of the leaf, upon which it usually sits in the
day-time, that you may have the leaf in your hand and yet not discover
ita.
- The tribe of grasshoppers, called
Locustæ by Fabricius, though the true
Locust does not belong to it, in the veining, colour, and texture
of their elytra, resemble green leavesb. -
The genera Mantis and Phasma - named prayîng-însects
and spectres - also of the Orthoptera order, often exhibit the
same peculiarity. - Others of them, by the spots and mixtures of colour
observable in these organs, repre sent leaves that are decaying in
various degrees. - Those of several species of Mantis likewise
imitate dry leaves, and so exactly, by their opacity, colour, rigidity,
and veins, that, were no other part of the animal visible, even after a
close examination, it would be generalty affirmed to be nothing but a
dry leaf. Of this nature is the Mantis
siccifolia, F., and two or three Brazilian species in my
cabinet, that seem undescribed, which I will show you when you give me
an opportunity. But these imitations of dry leaves are not confined
to the Orthoptera order solely. Amongst the Hemiptera,
the Coreus paradoxus, F., a kind
of bug, surprised Sparrman not a little. He was sheltering himself from
the mid-day sun, when the air was so still
and calm as scarcely to shake an aspen leaf, and saw with wonder what
he mistook for a littie withered pale, crumpled leaf, eaten as if were
by caterpillars, fluttering from the tree. The sight appeared to him so
very extraordinary, that he left his place of shelter to contemplate
it more nearly; and could scarcely believe his eyes, when he beheld a
living insect, in shape and colour resembling a fragment of a withered
leaf with the edges turned up and eaten away as it were by caterpillars,
and at the same time all over beset with prickles
a.
- British insect, one of our largest moths (Bombyx quercifolia, F.)
called by collectors the lappet-moth, affords an exarnple from
the Lepidoptera order of the imitation in question, as wings
representing, both in shape and colour, an arid brown leaf. Some bugs,
belonging to the genus Tingis, F.,
simulate portions of leaves in a still further state of decay, when the
veins only are left. For, the thorax and elytra of these insects being
reticulated, with the little areas or meshes of the net-work transparent,
this circumstance gives them exactly the appearance of small fragments
of skeletons of leaves.
But you have probably heard of most of these species of imitation:
I hope, therefore, you will give credit to the two instances
to which I shall next call your attention, of insects that even
mimic flowers and fruit. With respect to the former, I recollect
to have seen in a collection made by Mr. Masson at the Cape of
Good Hope, a kind of Pneumora,
Thunb. - arranged by Linné with the grasshoppers (Gryllus) - the elytra of which were of
a rose- or pink-colour, which,
the animal is suddenly brought from a state of motion to a state of rest
a.
This may very likely be one of their uses, but there are several circumstances
which militate against its being the only one. By their elasticity they
probably assist the insects that have them in their leaps; and when they climb
they may in some deg
gree act as suckers, and prevent them from falling.
But their use will be best ascertained by a review of the principal genera of
the order. Of these the cockroaches
(Blatta),
the spectres
(Phasma),
and the pray
ing insects
(Mantis),
are distinguished by tarsi of five
jointsb.
| a |
Philos. Trans. 1816. p. 325.
|
| b |
In a specimen in my cabinet of Blatta gigantea, the posterior
and anterior tarsi of one side have only four joints, while
the intemediate one has five. On the other side the hind leg is
broken off but the an terior and intermediate tarsi have both
five joints. In another specimen one posterior tarsus has four
and the other five joints.
|
The grasshoppers with setaceous antennæ (Locusta, F.) have four tarsal joints.
Those with filiform antennæ (Gryllus,
F. and Acrydium, F.), those
with ensiform (Truxalis, F.),
and the crickets (Acheta, F.),
have ouly three. In Blatta, the variations with respect to the
suckers and cushions (for many species are furnished with both) are
remarkable. The former in some (Blatta
gigantea, L.) are altogother wanting; in others
(B. Petiveriana,
L.) they are mere rudiments; and in others (B. Maderæ)
they are more conspicuous, and resemble those of tbe
Gryllidæ. The cushions also in some are nearly
obsolete, and occupy the mere extremity of the four first tarsal
joints (B. orientalis,
americana, capensis, &c.). In B. Petiveriana there is none upon
the first joint; but upon the extremity of
the four last, not excepting the claw-joint, there is a
minute orbicular concave one, resembling a sucker. In others
(B. gigantea, &c.) they extend the length of the four first
joints, and are very conspicuous.
|
a
|
This insect, which is remarkable for having the margin
of its thorax reflexed, was long since well figured in
Mouffet's work (130. fig. infima). It has not,
however, been described by any other author I have
met with. It is common in Brazil. Some specimens are
pallid, while others are of a dark brown.
|
|
b
|
De Geer, iii. 421. t. xxi. f. 13. h.
This author has also noticed the
cushions in this genus and Gryllus,
and the claw-sucker in the latter, which
he thinks are analogous to those of the fly.
Ibid. 462. t. xxii. f. 7-8.
|
|
c
|
Philo. Trans. 1816. t. xxi. f. 8-13.
|
In some (B. Mouffeli, K.a), which have no claw-sucker, there appears to be
a cavity in the extremity of the claw-joint, which may serve the purpose
of one. These cushions are usually of a pale colour; but in one specimen
of a hairy female which I have, from Brazil, they are black. The spectre
genus (Phasma) exhibits no particular varieties in this respect.
The tarsal joints of the legs have cushions at their apex, which appear
to be bifid. They have a large orbicular sucker be tween the claws.
In Mantis the fore feet have neither of the parts in question,
and the others have no suckers. They have cushions on the four first
tarsal joints of the two last pair of legs, which, though smaller, shaped
much like those in Phasma. In Locusta the feet have no
suckers between the claws, but they are distinguish ed by two oval, soft,
concave, and moveable processes attached to the of the first joint of the
tarsus, which probably act as suckersb.
In this genus there are two cushions on the first joint of the tarsi, and
one on each of the two following onesc. -
The species of
the Fabrician genus Gryllus come next. This genus is now
called Acrydium by Latreille after Geoffroy; but, since it
includes the true locust, it ought to have retained the name
Locusta given by Linné to the tribe to which it belongs.
All these insects have the terminal sucker between the claws, three
cushions on the first joint of the tarsus, and one on the seconda;
|
a
|
Philos. Trans. 1816, t. xxi. f. 1-9.
|
and the same conformation also distinguishes the feet of Truxalis,
F. In the species of Acrydium, F. (Tetrix, Latr.), the
cushions, I believe - for in the dead insect they are the reverse of
conspicuous - are arranged nearly as in the two preceding genera, but
these insects are without the claw-sucker. And lastly, Acheta,
F., has neither suckers nor cushions. From this statement it seems
to follow - since Blatta, Phasma, and Mantis,
that do not leap, are provided with cushions; and Acheta, F., a
heavy tribe of insects that does, are without them - that their object
cannot be exclusively to break the fall of the insects that have them.
And for the same reason we may conclude, that they must have some
further use than augmenting their elasticity when they jump. When we
consider that Blattæ - many of which have no suckers, or
very small ones - are climbing insects (I have seen B. germanica
run up and down the walls of an apartment with great agilily), and that
the long and gigantic apterous spectres &c. (Phasma) require
considerable means to enable them to climb the trees in which they feed,
and to maintain their station upon them, we may conclude that these
cushions, by acting in some degree as suckers, may promote these ends.
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