itself as a conical hole rather more than two inches deep, gradually
contracting to a point at the bottom, and about three inches wide at
the top[755]. The ant-lion now takes its station at the bottom of the
pit, and, that its gruff appearance may not scare the passengers which
approach its den, covers itself with sand all except the points of its
expanded forceps. It is not long before an ant on its travels, fearing
no harm, steps upon the margin of the pit, either accidentally or for
the purpose of exploring the depth below. Alas! its curiosity is dearly
gratified. The faithless sand slides from under its feet; its struggles
but hasten its descent; and it is precipitated headlong into the jaws
of the concealed devourer. Sometimes, however, it chances that the ant
is able to stop itself midway, and with all haste scrambles up again.
No sooner does the ant-lion perceive this, (for, being furnished with
six eyes on each side of his head, he is sufficiently sharp-sighted,)
than, shaking off his inactivity, he hastily shovels loads of sand upon
his head, and vigorously throws them up in quick succession upon the
escaping insect, which, attacked by such a heavy shower from below and
treading on so unstable a path, is almost inevitably carried to the
bottom. The instant his victim is fairly within reach, the ant-lion
seizes him between his jaws, which are admirable instruments, at the
same time hooked for holding, and hollow, furnished with a lateral
piston, for sucking, and at his leisure extracting all the juices of
the body, regales upon formic acid. The dry carcase he subsequently
jerks out of his den, that it may not encumber him in his future
contests, or betray the "horrid secrets of his prison-house:" and
if the sides of the pit have received any damage, he leaves his
concealment for awhile to repair it: which having done, he resumes his
station.
In this manner in its larva state this insect lives nearly two years,
during all which time it receives no food but what has been caught
through the artifice above described. Though all living insects, for
I have fed it with flies, are equally acceptable to it, as the winged
tribe can easily take flight from its pit should they chance to fall
into it, its prey consists chiefly of apterous species, of which ants
form by far the largest portion, with occasionally an unwary spider
or wood-louse. When the full period of its growth is attained it
retires under the sand; spins with its anus a silken cocoon; remains
a chrysalis a few weeks; and then breaks forth a four-winged insect
resembling, as before observed, the dragon-fly both in appearance and
manners, and preying in like manner on moths, butterflies, and other
insects[756].
The larva of _Myrmeleon Formicaleo_ is not the only insect which
avails itself of a trap for obtaining its prey. A plan in most
respects similar is adopted by that of a fly (_Leptis Vermileo_) in
form somewhat resembling the common flesh maggot. This also digs a
funnel-shaped cavity in loose earth or sand, but deeper in proportion
to its width than that of _M. Formicaleo_, and excavated not by regular
circles, but by throwing out the earth obliquely on all sides. When its
trap is finished, it stretches itself near the bottom, remaining stiff
and without motion like a piece of wood, and the last segment bent at
an angle with the rest, so as to form a strong point of support in the
struggles which it often necessarily has with vigorous prey. The moment
an insect falls into the pitfall, the larva writhes itself round it
like a serpent, transfixes it with its mandibles, and sucks its juices
at its ease. If the insect escapes, the larva casts above it jets of
sand with surprising rapidity[757].
I am, &c.
FOOTNOTES:
[735] Reaum. _Mem. de l'Acad. de Paris_, An. 1713.211.--De Geer, vii.
187. See also Hoole's _Leeuwenhoek_, i. 41.--_t._ 2. _f._ 20-22.
Leeuwenhoek examined a spinner that was not so big as a common grain
of sand, and the number of tubes issuing from it was more than a
hundred. He affirms that, besides the larger spinners, in the space
between them there are four smaller ones, each furnished with organs
for spinning threads, but smaller and fewer in number. Latreille
speaks only of a thousand spinners from each teat, and of six
thousand threads from the whole--but he does not enter further into
the subject. _Nouv. Dict. d'Hist. Nat._ ii. 278.
[736] _Hist. Anim. Ang._ p. 8.
[737] De Geer, vii. 189.
[738] Leeuw. _Opusc._ iii. 317. f. 1.
[739] 1 Sam. xxiv. 4.
[740] Lesser, _L._ ii. 291.
[741] L. xi. c. 24.
[742] I am not certain whether the garden spider does not more
frequently form one or two of the principal radii of the net, before
she spins the exterior lines.
[743] _Treatise on the Apple and Pear_, p. 97.
[744] Some time after making this experiment I stumbled upon a
passage in Redi (_De Insectis_, p. 119.) from which it appears that
Blancanus, in his _Commentaries upon Aristotle_, has related a series
of observations which led him to precisely the same result. Lehmann,
too, in a paper in the _Transactions of the Society of Naturalists at
Berlin_ (translated in the _Philosophical Magazine_, xi. 323.) has
given an explanation somewhat similar of the operations of this very
spider, but I am inclined to think erroneous in some particulars.
He describes it as emitting _numerous_ floating threads at the
_commencement_ of its descent. That he is mistaken in supposing these
threads to be more than one, is proved by the fact which I have
observed--that even that one sometimes breaks by the weight of the
spider. How then could an insect almost as big as a gooseberry be
supported by a line of the tenuity here attributed to it?
[745] _An._ vii. _Vindemiaire_. Translated in _Phil. Mag._ ii. 275.
[746] _Hist. Anim. Ang._ p. 7.
[747] Plin. _Hist. Nat._ l. xi. c. 17.
[748] May not the spinners mentioned by Leeuwenhoek (see above p.
404, note) be peculiar to the retiary spiders, and furnish this
viscid thread?
[749] Brez, _La Flore des Insectophiles_, 129.
[750] Lister, _Hist. Anim. Ang._ 32, tit. 4.
[751] _Phil. Tr._ 1668, p. 792.
[752] _Embassy to China_, i. 343.
[753] _Bemerkungen auf einer Reise um die Welt._ i. 63.
[754] PLATE XIX. FIG. 8.
[755] The nests of this animal which I saw at Fontainebleau (in
the pit producing the fossil named after that place) were scarcely
half the dimensions here given, but they might probably be younger
insects. I kept one in a box of sand several days, in which it
regularly formed its pit, whenever obliterated by shaking. The bottom
of the box unfortunately came out as I was upon my return to England,
and the animal was killed.
[756] Reaum. vi. 333-78. Bonnet, ii. 380.
[757] Bonnet, ix. 414. De Geer, vi. 168. _t._ 10.
LETTER XIV.
_HABITATIONS OF INSECTS._
In forming an estimate of the civilization and intellectual progress
of a newly discovered people, we usually pay attention to their
buildings, and other proofs of architectural skill. If we find
them, like the wretched inhabitants of Van Diemen's Land, without
other abodes than natural caverns or miserable penthouses of bark,
we at once regard them as the most ignorant and unhumanized of
their race. If, like the natives of the South Sea Isles, they have
advanced a step further, and enjoy houses formed of timber, thatched
with leaves, and furnished with utensils of different kinds, we
are inclined to place them considerably higher in the scale. When,
as in the case of ancient Mexico, we discover a nation inhabiting
towns containing stone houses, regularly disposed into streets, we
do not hesitate without other inquiry to decide that it must have
been civilized in no ordinary degree. And if it were to chance that
some future Park in Africa should stumble upon the ruins of a large
city, where, in addition to these proofs of science, every building
was constructed on just geometrical and architectural principles;
where the materials were so employed as to unite strength with
lightness, and a confined site so artfully occupied as to obtain
spacious symmetrical apartments, we should eagerly inquire into the
history of the inhabitants, and sigh over the remains of a race
whose intellectual advances we should infer with certainty were not
inferior to our own.
Were we by the same test to estimate the sagacity of the different
classes of animals, we should beyond all doubt assign the highest
place to insects, which in the construction of their habitations
leave all the rest far behind. The nests of birds, from the
rook's rude assemblage of sticks to the pensile dwellings of the
tailor-bird, wonderful as they doubtless are, are indisputably
eclipsed by the structures formed by many insects; and the regular
villages of the beaver, by far the most sagacious architect amongst
quadrupeds, must yield the palm to a wasp's nest. You will think me
here guilty of exaggeration, and that, blinded by my attachment to a
favourite pursuit, I am elevating the little objects, which I wish to
recommend to your study, to a rank beyond their just claim. So far,
however, am I from being conscious of any such prejudice, that I do
not hesitate to go further, and assert that the pyramids of Egypt, as
the work of man, are not more wonderful for their size and solidity
than are the structures built by some insects.
To describe the most remarkable of these is my present object: and
that some method may be observed, I shall in this letter describe the
habitations of insects living in a state of solitude, and built each by
a single architect; and in a subsequent one, those of insects living in
societies, built by the united labours of many. The former class may be
conveniently subdivided into habitations built by the parent insect,
not for its own use, but for the convenience of its future young; and
those which are formed by the insect that inhabits them for its own
accommodation. To the first I shall now call your attention.
* * * * *
The solitary insects which construct habitations for their future
young without any view to their own accommodation, chiefly belong
to the order _Hymenoptera_, and are principally different species
of wild bees. Of these the most simple are built by _Colletes_[758]
_succincta_, _fodiens_, &c. The situation which the parent bee
chooses, is either the dry earth of a bank, or the vacuities of stone
walls cemented with earth instead of mortar. Having excavated a
cylinder about two inches in depth, running usually in a horizontal
direction, the bee occupies it with three or four cells about half
an inch long, and one-sixth broad, shaped like a thimble, the end of
one fitting into the mouth of another. The substance of which these
cells are formed is two or three layers of a silky membrane, composed
of a kind of glue secreted by the animal, resembling gold-beater's
leaf, but much finer, and so thin and transparent that the colour of
an included object may be seen through them. As soon as one cell is
completed, the bee deposits an egg within, and nearly fills it with a
paste composed of pollen and honey; which having done, she proceeds
to form another cell, storing it in like manner until the whole is
finished, when she carefully stops up the mouth of the orifice with
earth. Our countryman Grew seems to have found a series of these
nests in a singular situation--the middle of the pith of an old
elder-branch--in which they were placed lengthwise one after another
with a thin boundary between each[759].
Cells composed of a similar membranaceous substance, but placed in a
different situation, are constructed by _Anthidium manicatum_[760].
This gay insect does not excavate holes for their reception, but places
them in the cavities of old trees, or of any other object that suits
its purpose. Sir Thomas Cullum discovered the nest of one in the inside
of the lock of a garden-gate, in which I have also since twice found
them. It should seem, however, that such situations would be too cold
for the grubs without a coating of some non-conducting substance. The
parent bee, therefore, after having constructed the cells, laid an
egg in each, and filled them with a store of suitable food, plasters
them with a covering of vermiform masses, apparently composed of honey
and pollen; and having done this, aware, long before Count Rumford's
experiments, what materials conduct heat most slowly, she attacks the
woolly leaves of _Stachys lanata_, _Agrostemma coronaria_, and similar
plants, and with her mandibles industriously scrapes off the wool,
which with her fore legs she rolls into a little ball and carries to
her nest. This wool she sticks upon the plaster that covers her cells,
and thus closely envelops them with a warm coating of down impervious
to every change of temperature[761].
The bee last described may be said to exercise the trade of a clothier.
Another numerous family would be more properly compared to carpenters,
boring with incredible labour out of the solid wood long cylindrical
tubes, and dividing them into various cells. Amongst these, one of
the most remarkable is _Xylocopa_[762] _violacea_, a large species, a
native of Southern Europe, distinguished by beautiful wings of a deep
violet colour, and found commonly in gardens, in the upright putrescent
espaliers or vine-props of which, and occasionally in the garden seats,
doors and window-shutters, she makes her nest. In the beginning of
spring, after repeated and careful surveys, she fixes upon a piece of
wood suitable for her purpose, and with her strong mandibles begins
the process of boring. First proceeding obliquely downwards, she soon
points her course in a direction parallel with the sides of the wood,
and at length with unwearied exertion forms a cylindrical hole or
tunnel not less than twelve or fifteen inches long and half an inch
broad. Sometimes, where the diameter will admit of it, three or four
of these pipes, nearly parallel with each other, are bored in the same
piece. Herculean as this task, which is the labour of several days,
appears, it is but a small part of what our industrious bee cheerfully
undertakes. As yet she has completed but the shell of the destined
habitation of her offspring; each of which, to the number of ten or
twelve, will require a separate and distinct apartment. How, you will
ask, is she to form these? With what materials can she construct the
floors and ceilings? Why truly GOD "doth instruct her to discretion
and doth teach her." In excavating her tunnel she has detached a large
quantity of fibres, which lie on the ground like a heap of saw-dust.
This material supplies all her wants. Having deposited an egg at the
bottom of the cylinder along with the requisite store of pollen and
honey, she next, at the height of about three quarters of an inch,
(which is the depth of each cell,) constructs of particles of the
saw-dust glued together, and also to the sides of the tunnel, what may
be called an annular stage or scaffolding. When this is sufficiently
hardened, its interior edge affords support for a second ring of the
same materials, and thus the ceiling is gradually formed of these
concentric circles, till there remains only a small orifice in its
centre, which is also closed with a circular mass of agglutinated
particles of saw-dust. When this partition, which serves as the ceiling
of the first cell and the flooring of the second, is finished, it is
about the thickness of a crown-piece, and exhibits the appearance of as
many concentric circles as the animal has made pauses in her labour.
One cell being finished, she proceeds to another, which she furnishes
and completes in the same manner, and so on until she has divided her
whole tunnel into ten or twelve apartments.
Here, if you have followed me in this detail with the interest which
I wish it to inspire, a query will suggest itself. It will strike you
that such a laborious undertaking as the constructing and furnishing
these cells, cannot be the work of one or even of two days.
Considering that every cell requires a store of honey and pollen, not
to be collected but with long toil, and that a considerable interval
must be spent in agglutinating the floors of each, it will be very
obvious to you that the last egg in the last cell must be laid many
days after the first. We are certain, therefore, that the first egg
will become a grub, and consequently a perfect bee, many days before
the last. What then becomes of it? you will ask. It is impossible
that it should make its escape through eleven superincumbent cells
without destroying the immature tenants; and it seems equally
impossible that it should remain patiently in confinement below
them until they are all disclosed. This dilemma our heaven-taught
architect has provided against. With forethought never enough to be
admired she has not constructed her tunnel with one opening only,
but at the further end has pierced _another_ orifice, a kind of
back-door, through which the insects produced by the first-laid eggs
successively emerge into day. In fact, all the young bees, even the
uppermost, go out by this road; for, by an exquisite instinct, each
grub, when about to become a pupa, places itself in its cell with its
head downwards, and thus is necessitated, when arrived at its last
state, to pierce its cell in this direction[763].
_Ceratina albilabris_ of Spinola, who has given an interesting
account of its manners, forms its cell upon the general plan of the
bee just described, but, more economical of labour, chooses a branch
of briar or bramble, in the pith of which she excavates a canal about
a foot long and one line, or sometimes more, in diameter, with from
eight to twelve cells separated from each other by partitions of
particles of pith glued together[764].
Such are the curious habitations of the carpenter bees. Next I shall
introduce you to the not less interesting structures of another
family which carry on the trade of masons, (_Megachile muraria_,)
building their solid houses solely of artificial stone. The first
step of the mother bee is to fix upon a proper situation for the
future mansion of her offspring. For this she usually selects an
angle, sheltered by any projection, on the south side of a stone
wall. Her next care is to provide materials for the structure. The
chief of these is sand, which she carefully selects grain by grain
from such as contains some mixture of earth. These grains she glues
together with her viscid saliva into masses the size of small shot,
and transports by means of her jaws to the site of her castle[765].
With a number of these masses, which are the artificial stone of
which her building is to be composed, united by a cement preferable
to ours, she first forms the basis or foundation of the whole. Next
she raises the walls of a cell, which is about an inch in length
and half an inch broad, and before its orifice is closed in form
resembles a thimble. This, after depositing an egg and a supply of
honey and pollen, she covers in, and then proceeds to the erection
of a second, which she finishes in the same manner, until the whole
number, which varies from four to eight, is completed. The vacuities
between the cells, which are not placed in any regular order, some
being parallel to the wall, others perpendicular to it, and others
inclined to it at different angles, this laborious architect fills
up with the same material of which the cells are composed, and then
bestows upon the whole group a common covering of coarser grains of
sand. The form of the whole nest, which when finished is a solid mass
of stone so hard as not to be easily penetrated with the blade of a
knife, is an irregular oblong of the same colour as the sand, and to
a casual observer more resembling a splash of mud than an artificial
structure. These bees sometimes are more economical of their labour,
and repair old nests, for the possession of which they have very
desperate combats. One would have supposed that the inhabitants of a
castle so fortified might defy the attacks of every insect marauder.
Yet an Ichneumon and a beetle (_Clerus apiarius_) both contrive to
introduce their eggs into the cells, and the larvæ proceeding from
them devour their inhabitants[766].
Other bees of the same family with that last described, use different
materials in the construction of their nests. Some employ fine
earth made into a kind of mortar with gluten. Another (_Osmia_[767]
_cærulescens_), as we learn from De Geer, forms its nest of
argillaceous earth mixed with chalk, upon stone walls, and sometimes
probably nidificates in chalk-pits. _O. bicornis_ selects the hollows
of large stones for the site of its dwelling; while others prefer the
holes in wood.
The works thus far described require in general less genius than
labour and patience: but it is far otherwise with the nests of
the last tribe of artificers amongst wild bees, to which I shall
advert--the hangers of tapestry, or upholsterers--those which line
the holes excavated in the earth for the reception of their young,
with an elegant coating of flowers or of leaves. Amongst the most
interesting of these is _Megachile_[768] _Papaveris_, a species whose
manners have been admirably described by Reaumur. This little bee,
as though fascinated with the colour most attractive to our eyes,
invariably chooses for the hangings of her apartments the most
brilliant scarlet, selecting for its material the petals of the wild
poppy, which she dexterously cuts into the proper form. Her first
process is to excavate in some pathway a burrow, cylindrical at the
entrance but swelled out below, to the depth of about three inches.
Having polished the walls of this little apartment, she next flies
to a neighbouring field, cuts out oval portions of the flowers of
poppies, seizes them between her legs and returns with them to her
cell; and though separated from the wrinkled petal of a half-expanded
flower, she knows how to straighten their folds, and, if too large,
to fit them for her purpose by cutting off the superfluous parts.
Beginning at the bottom, she overlays the walls of her mansion with
this brilliant tapestry, extending it also on the surface of the
ground round the margin of the orifice. The bottom is rendered warm
by three or four coats, and the sides have never less than two. The
little upholsterer, having completed the hangings of her apartment,
next fills it with pollen and honey to the height of about half an
inch; then, after committing an egg to it, she wraps over the poppy
lining so that even the roof may be of this material; and lastly
closes its mouth with a small hillock of earth[769]. The great depth
of the cell compared with the space which the single egg and the
accompanying food deposited in it occupy, deserves particular notice.
This is not more than half an inch at the bottom, the remaining
two inches and a half being subsequently filled with earth.--When
you next favour me with a visit, I can show you the cells of this
interesting insect as yet unknown to British entomologists, for
which I am indebted to the kindness of M. Latreille, who first
scientifically described the species[770].
_Megachile centuncularis_, _M. Willughbiella_, and other species
of the same family, like the preceding, cover the walls of their
cells with a coating of leaves, but are content with a more sober
colour, generally selecting for their hangings the leaves of trees,
especially of the rose, whence they have been known by the name
of the _leaf-cutter_ bees. They differ also from _M. Papaveris_
in excavating longer burrows, and filling them with several
thimble-shaped cells composed of portions of leaves so curiously
convoluted, that, if we were ignorant in what school they have been
taught to construct them, we should never credit their being the
work of an insect. Their entertaining history, so long ago as 1670,
attracted the attention of our countrymen Ray, Lister, Willughby, and
Sir Edward King; but we are indebted for the most complete account of
their procedures to Reaumur.