have observed, they fly up and down with a zigzag course; at others
in vertical curves of small diameter, like some birds; at others,
again, in horizontal curves:--all these lines they describe with a
kind of skipping motion. Sometimes they would seem to flit in every
possible way--upwards, downwards, athwart, obliquely, and sometimes
almost in circles. The common gnat (_Culex pipiens_) seems to sail
along also in various directions. The motion of its wings, if it does
not fly like a hawk, is so rapid as not to be perceptible. When
the crane-fly (_Tipula oleracea_) is upon the wing, its fore-legs
are placed horizontally, pointing forwards, and the four hind ones
stretched out in an opposite direction, the one forming the prow and
the other the stern of the vessel, in its voyage through the ocean of
air. The legs of another insect of this tribe (_Hirtæa Marci_) all
point towards the anus in flight, the long anterior pair forming an
acute angle with the body:--thus, perhaps, it can better cut the air.
I have often been amused in my walks with the motions of the
hornet-fly (_Asilus crabroniformis_), belonging to the second
division just mentioned. This insect is carnivorous, living upon
small flies. When you are taking your rambles, you may often observe
it alight just before you;--as soon as you come up, it flies a little
further, and will thus be your avant-courier for the whole length
of a long field. This usually takes place, I seem to have observed,
when a path lies under a hedge; and perhaps the object of this
manœuvre may be the capture of prey. Your motions may drive a number
of insects before you, and so be instrumental in supplying it with a
meal. Other species of the genus have the same habit.
The aërial progress of the fly tribes, including the gad-flies
(_Œstridæ_); horse-flies (_Tabanidæ_); carrion-flies (_Muscidæ_),
and many other genera--which constitute the heavy horse amongst
our two-winged fliers--is wonderfully rapid, and usually in a
direct line. An anonymous observer in Nicholson's _Journal_[577]
calculates that, in its ordinary flight, the common house-fly (_Musca
domestica_) makes with its wings about 600 strokes, which carry it
five feet, every second. But if alarmed, he states their velocity
can be increased six- or seven-fold, or to thirty or thirty-five
feet, in the same period. In this space of time a race-horse could
clear only ninety feet, which is at the rate of more than a mile in
a minute. Our little fly, in her swiftest flight, will in the same
space of time go more than the third of a mile. Now compare the
infinite difference of the size of the two animals (ten millions of
the fly would hardly counterpoise one racer), and how wonderful will
the velocity of this minute creature appear! Did the fly equal the
race-horse in size, and retain its present powers in the ratio of its
magnitude, it would traverse the globe with the rapidity of lightning.
It seems to me, that it is not by muscular strength alone that many
insects are enabled to keep so long upon the wing. Every one who
attends to them must have noticed, that the velocity and duration
of their flights depend much upon the heat or coolness of the
atmosphere: especially the appearance of the sun. The warmer and
more unclouded his beam, the more insects are there upon the wing,
and every diurnal species seems fitted for longer or more frequent
excursions. As these animals have no circulating fluid except the
air in their tracheæ and bronchiæ, their locomotive powers, with few
exceptions, must depend altogether upon the state of that element.
When the thermometer descends below a certain point they become
torpid, and when it reaches a certain height they revive; so that
the air must be regarded, in some sense, as their blood, or rather
the caloric that it contains; which when conveyed by the air, it
circulates quickly in them, invigorates all their motions, enters
into the muscles and nervures of their wings, maintaining their
tension, and by the greater or less rapidity of its pulsations
accelerating or diminishing their action.
Having given you all the information that I can collect with respect
to the motions of perfect insects in the _air_, I must next say
something concerning their modes of locomotion in or upon the
_water_. These are of two kinds, _swimming_ and _walking_. Observe--I
call that movement swimming, in which the animal pushes itself along
by strokes--while in walking, the motion of the legs is not different
from what it would be if they were on land. Most insects that _swim_
have their posterior legs peculiarly fitted for it, either by a
dense fringe of hairs on the shank and foot, as in the water-beetles
(_Dytiscus_)[578], or the water-boatmen (_Notonecta_); or by
having their terminal joints very much dilated--as in the whirlwig
(_Gyrinus_)--so as to resemble the paddle of an oar[579]. When the
Dytisci rise to the surface to take in fresh air--a silver bubble
of which may often be seen suspended at their anus--they ascend, as
it should seem, merely in consequence of their being specifically
lighter than the water; but when they descend or move horizontally,
which they do with considerable rapidity, it is by regular and
successive strokes of their swimming legs. While they remain
suspended at the surface, these legs are extended so as to form a
right angle with their body. The water-boatmen swim upon their back,
which enables them to see readily and seize the insects that fall
upon the water, which are their prey. _Sigara_, however, a cognate
genus separated from _Notonecta_ by Fabricius, swims in the ordinary
way. As the Gyrini are usually in motion at the surface, whirling
round and round in circles, it is probable that their legs are best
adapted to this movement. They dive down, however, with great ease
and velocity when alarmed. The common water-bug (_Gerris lacustris_),
though it never goes under water, will sometimes swim upon the
surface, which it does by strokes of the intermediate and posterior
legs[580]. These, however, are neither fringed nor dilated, but very
long and slender, with claws, not easily detected, situated under
the apex of the last joint of the foot, which covers and conceals
them. The underside of their body--as is the case with _Elophorus_,
and many other aquatic insects--is clothed with a thick coat of gray
hairs like satin, which in certain lights have no small degree of
lustre, and protect its body from the effects of the water. Some
insects, that are not naturally aquatic, if they fall into the water
will swim very well. I once saw a kind of grasshopper (_Acrydium_),
which by the powerful strokes of its hind legs pushed itself across a
stream with great rapidity.
Other insects _walk_, as it were, in the water, moving their legs
much in the same way as they would do on the land. Many smaller
species of water-beetles, belonging to the genera _Hydrophilus_,
_Elophorus_, _Hydræna_, _Parnus_, _Limnius_, &c. thus win their way
in the waves.--Thus also the water-scorpion (_Nepa_) pursues its
prey; and the little water-mites (_Hydrachna_) may be seen in every
pool thus working their little legs with great rapidity, and moving
about in all directions.--Some spiders also will not only traverse
the surface of the waters, but, as you have heard with respect to
one[581], descend into their bosom. There are other insects moving
in this way that are not divers. Of this kind are the aquatic bugs
(_Gerris lacustris_, _Hydrometra Stagnorum_, _Velia Rivulorum_, &c.
Latr.). The first can walk, run, and even leap, which it does upon
its prey, as well as swim upon the surface. The second, remarkable
for its extreme slenderness, and for its prominent hemispherical
eyes--which, though they are really in the head, appear to be in
the middle of the body--rambles about in chase of other insects, in
considerable numbers, in most stagnant waters. The _Velia_ is to be
met with chiefly in running streams and rivers, coursing very rapidly
over their waves[582]. The two last species neither jump nor swim.
I am next to say a few words upon the motions of insects that
_burrow_, either to conceal themselves or their young. Though
burrowing is not always a locomotion, I shall consider it under this
head, to preserve the unity of the subject. Many enter the earth by
means of fore-legs particularly formed for the purpose. The flat
dentated anterior shanks, with slender feet, that distinguish the
chafers (_Petalocera_)--most of which in their first states live
under ground, and many occasionally in their last--enable them to
make their way either into the earth or out of it. Two other genera
of beetles (_Scarites_ and _Clivina_, Latr.)[583] have these shanks
palmated, or armed with longer teeth at their extremity, for the
same purpose. But the most remarkable burrower amongst perfect
insects is that singular animal the mole-cricket (_Gryllotalpa
vulgaris_)[584]. This creature is endowed with wonderful strength,
particularly in its thorax and fore legs. The former is a very hard
and solid shell or crust, covering like a shield the trunk of the
animal; and the latter are remarkably fitted for burrowing, both
by their strength and construction. The shanks are very broad, and
terminate obliquely in four enormous sharp teeth[585], like so many
fingers: the foot consists of three joints--the two first being
broad and tooth-shaped, and pointing in an opposite direction to the
teeth of the shank; and the last small, and armed at the extremity
with two short claws. This foot is placed inside the shank, so as to
resemble a thumb and perform the office of one[586]. The direction
and motion of these hands, as in moles, is outwards; thus enabling
the animal most effectually to remove the earth when it burrows.
By the help of these powerful instruments, it is astonishing how
instantaneously it buries itself. This creature works under ground
like a field-mouse, raising a ridge as it goes; but it does not
throw up heaps like its name-sake the mole. They will in this manner
undermine whole gardens; and thus in wet and swampy situations, in
which they delight, they excavate their curious apartments, before
described. The field-cricket (_Gryllus campestris_) is also a
burrower, but by means of different instruments; for with its strong
jaws, toothed like the claws of a lobster, but sharper, in heaths and
other dry situations it perforates and rounds its curious and regular
cells. The house-cricket (_G. domesticus_), which, on account of the
softness of the mortar, delights in new-built houses, with the same
organs, to make herself a covered-way from room to room, burrows and
mines between the joints of the bricks and stones[587].
But of all the burrowing tribes, none are so numerous as those
of the order _Hymenoptera_. Wherever you see a bare bank, of a
sunny exposure, you always find it full of the habitations of
insects belonging to it;--and besides this, every rail and old
piece of timber is with the same view perforated by them. Bees;
wasps; bee-wasps (_Bembex_); spider-wasps (_Pompilus_); fly-wasps
(_Mellinus_, _Cerceris_, _Crabro_), with many others, excavate
subterranean or ligneous habitations for their young. None is more
remarkable in this respect than the sand-wasp (_Ammophila_), or
as it might be better named--since it always commits its eggs to
caterpillars which it inhumes--the caterpillar-wasp. It digs its
burrows, by scratching with its fore legs like a dog or a rabbit,
dispersing with its hind ones, which are particularly constructed for
that purpose, the sand so collected[588].
Since most of these burrows are designed for the reception of the eggs
of the burrowers, I shall next describe to you the manner in which
one of the long-legged gnats, or crane-flies (_Tipula variegata_,)--a
proceeding to which I was myself a witness--oviposits. Choosing a south
bank bare of grass, she stood with her legs stretched out on each side,
and kept turning herself half round backwards and forwards alternately.
Thus the ovipositor, which terminates her long cylindrical pointed
abdomen, made its way into the hard soil, and deposited her eggs in a
secure situation. All, however, were not committed to the same burrow;
for she every now and then shifted her station, but not more than an
inch from where she bored last. While she was thus engaged, I observed
her male companion suspended by one of his legs on a twig, not far from
her. The common turf-boring crane-fly (_T. oleracea_), when engaged in
laying eggs, moves over the grass with her body in a vertical position,
by the help--her four anterior legs being in the air--of her two
posterior ones, and the end of her abdomen, which performs the office
of another. Whether in boring, like _T. variegata_, she turns half
round and back, does not appear from Reaumur's account[589].
I now come to motions whose object seems to be _sport_ and amusement
rather than locomotion. They may be considered as of three
kinds--hovering--gyrations--and dancing.
You have often in the woods and other places seen flies suspended
as it were in the air, their wings all the while moving so rapidly
as to be almost invisible. This _hovering_, which seems peculiar to
the aphidivorous flies, has been also noticed by De Geer[590]. I
have frequently amused myself with watching them; but when I have
endeavoured to entrap them with my forceps, they have immediately
shifted their quarters, and resumed their amusement elsewhere. The
most remarkable insects in this respect are the sphinxes, and from
this they doubtless took their name of _hawk-moths_. When they unfold
their long tongue, and wipe its sweets from any nectariferous flower,
they always keep upon the wing, suspending themselves over it till
they have exhausted them, when they fly away to another. The species
called by collectors the humming-bird (_Macroglossa Stellatarum_),
and by some persons mistaken for a real one, is remarkable for this,
and the motion of its wings is inconceivably rapid[591].
The _gyrations_ of insects take place either when they are reposing,
or when they are flying or swimming.--I was once much diverted by
observing the actions of a minute moth upon a leaf on which it was
stationed. Making its head the centre of its revolutions, it turned
round and round with considerable rapidity, as if it had the vertigo,
for some time. I did not, however, succeed in my attempts to take
it.--Scaliger noticed a similar motion in the book-crab (_Chelifer
cancroides_)[592].
Reaumur describes in a very interesting and lively way the gyrations
of the Ephemeræ before noticed[593], round a lighted flambeau. It is
singular, says he, that moths which fly only in the night, and shun
the day, should be precisely those that come to seek the light in our
apartments. It is still more extraordinary that these Ephemeræ--which
appearing after sunset, and dying before sun-rise, are destined never
to behold the light of that orb--should have so strong an inclination
for any luminous object. To hold a flambeau when they appeared was no
very pleasant office; for he who filled it, in a few seconds had his
dress covered with the insects, which rushed from all quarters to him.
The light of the flambeau exhibited a spectacle which enchanted every
one that beheld it. All that were present, even the most ignorant
and stupid of his domestics, were never satisfied with looking at
it. Never had any armillary sphere so many zones, as there were here
circles, which had the light for their centre. There was an infinity of
them--crossing each other in all directions, and of every imaginable
inclination--all of which were more or less eccentric. Each zone was
composed of an unbroken string of Ephemeræ, resembling a piece of
silver lace formed into a circle deeply notched, and consisting of
equal triangles placed end to end (so that one of the angles of that
which followed touched the middle of the base of that which preceded),
and moving with astonishing rapidity. The wings of the flies, which was
all of them that could then be distinguished, formed this appearance.
Each of these creatures, after having described one or two orbits,
fell upon the earth or into the water, but not in consequence of being
burned[594]. Reaumur was one of the most accurate of observers; and
yet I suspect that the appearance he describes was a visual deception,
and for the following reason. I was once walking in the day-time with
a friend[595], when our attention was caught by myriads of small
flies, which were dancing under every tree;--viewed in a certain light
they appeared a concatenated series of insects (as Reaumur has here
described his Ephemeræ) moving in a spiral direction upwards;--but
each series upon close examination, we found was produced by the
astonishingly rapid movement of a single fly. Indeed, when we consider
the space that a fly will pass through in a second, it is not wonderful
that the eye should be unable to trace its gradual progress, or that it
should appear present in the whole space at the same instant. The fly
we saw was a small male Ichneumon.
Other circular motions of sportive insects take place in the waters.
Linné, in his Lapland tour, noticed a black Tipula which ran over the
water, and turned round like a whirlwig, or _Gyrinus_[596]. This last
insect I have often mentioned;--it seems the merriest and most agile of
all the inhabitants of the waves. Wonderful is the velocity with which
they turn round and round, as it were pursuing each other in incessant
circles, sometimes moving in oblique, and indeed in every other
direction. Now and then they repose on the surface, as if fatigued with
their dances, and desirous of enjoying the full effect of the sun-beam:
if you approach they are instantaneously in motion again. Attempt to
entrap them with your net, and they are under the water and dispersed
in a moment. When the danger ceases they reappear, and resume their
vagaries. Covered with lucid armour, when the sun shines they look like
little dancing masses of silver or brilliant pearls[597].
But the motions of this kind to which I particularly wish to call
your attention, are the choral dances of males in the air; for the
dancing sex amongst insects is the masculine, the ladies generally
keeping themselves quiet at home. These dances occur at all seasons
of the year, both in winter and summer, though in the former
season they are confined to the hardy Tipulariæ. In the morning
before twelve, the _Hopliæ_, root-beetles before mentioned, have
their dances in the air, and the solstitial and common cockchafer
appear in the evening--the former generally coming forth at the
summer solstice--and fill the air over the trees and hedges with
their myriads and their hum. Other dancing insects resemble moving
columns--each individual rising and falling in a vertical line a
certain space, and which will follow the passing traveller--often
intent upon other business, and all unconscious of his aërial
companions--for a considerable distance.
Towards sun-set the common Ephemeræ (_E. vulgata_), distinguished
by their spotted wings and three long tails (_Caudulæ_), commence
their dances in the meadows near the rivers. They assemble in
troops, consisting sometimes of several hundreds, and keep rising
and falling continually, usually over some high tree. They rise
beating the air rapidly with their wings, till they have ascended
five or six feet above the tree; then they descend to it with their
wings extended and motionless, sailing like hawks, and having their
three tails elevated, and the lateral ones so separated as to form
nearly a right angle with the central one. These tails seem given
them to balance their bodies when they descend, which they do in a
horizontal position. This motion continues two or three hours without
ceasing, and commences in fine clear weather about an hour before
sun-set, lasting till the copious falling of the dew compels them to
retire to their nocturnal station[598]. Our most common species,
which I have usually taken for the _E. vulgata_, varies from that of
De Geer in its proceedings. I found them at the end of May dancing
over the meadows, not over the trees, at a much earlier hour--at
half-past three--rising in the way just described, about a foot, and
then descending, at the distance of about four or five feet from the
ground. Another species, common here, rises seven or eight feet.
I have also seen Ephemeræ flying over the water in a horizontal
direction. The females are sometimes in the air, when the males seize
them, and they fly paired. These insects seem to use their fore-legs
to break the air; they are applied together before the head, and look
like antennæ.--_Hilara maura_, a little beaked fly, I have observed
rushing in infinite numbers like a shower of rain driven by the wind,
as before observed[599], over waters, and then returning back.
It is remarkable that the smaller _Tipulariæ_ will fly unwetted in
a heavy shower of rain, as I have often observed. How keen must be
their sight, and how rapid their motions, to enable them to steer
between drops bigger than their own bodies, which, if they fell upon
them, must dash them to the ground!
Amidst this infinite variety of motions, for purposes so numerous and
diversified, and performed by such a multiplicity of instruments and
organs, who does not discern and adore the Great FIRST MOVER? From
him all proceed, by him all are endowed, in him all move: and it is
to accomplish his ends, and to go on his errands, that these little
but not insignificant beings are thus gifted; since it is by them
that he maintains this terraqueous globe in order and beauty, thus
rendering it fit for the residence of his creature man.
I am, &c.
FOOTNOTES:
[468] Peck in _Linn. Trans._ xi. 92.
[469] Meigen considers this as an _Ortalis_; but its peculiar habit
of constantly vibrating its wings indicates a distinct genus:
especially as the habit is not confined to a single species.
[470] De Geer, vi. 335.
[471] See above, p. 234.
[472] The most common number of joints in the tarsus is from two to
five; but the Phalangidæ have sometimes more than forty. In these,
under a lens, this part looks like a jointed antenna.
Geoffroy, and after him most modern entomologists, has taken the
_primary_ divisions of the _Coleoptera_ order from the number of
joints in the tarsus; but this, although perhaps in the majority
of cases it may afford a natural division, will not universally.
For--not to mention the instance of _Pselaphus_, clearly belonging to
the _Brachyptera_--both _Oxytelus_, Grav., and another genus that I
have separated from it (_Carpalimus_, K. Ms.), have only two joints
in their tarsi. In this tribe, therefore, it can only be used for
secondary divisions.--K.
[473] iii. 284.
[474] _Hist. Ins._ 10.
[475] Redi _Opusc._ i. 80. Amoreux, 44--.
[476] _Œuvr._ ii. 426.
[477] Lesser, _L._ i. 248, note 24.
[478] _Linn. Trans._ xi. 13.
[479] Marsham in _Linn. Trans._ iii. 26--.
[480] De Geer, iii. 324--.
[481] _Brit. Ent._ i. _t._ xxx. _f._ 4.
[482] Cuvier, _Anat. Comp._ i. 496--.
[483] Oliv. _Entom._ n. 90. _t._ i.
[484] Swamm. _Bibl. Nat._ Ed. Hill, i. 123. b.
[485] Aristoph. _Nubes_, Act. i. Sc. 2.
[486] Trost, _Beiträge_, 40.
[487] De Geer, iii. 161.
[488] De Geer, iii. 178.
[489] Evelyn, quoted in Hooke's _Microgr._ 200--.
[490] _Anat. Comp._ i. 498.
[491] ii. 910.
[492] PLATE XV. FIG. 14.
[493] De Geer, vii. 38-- _t._ iii. _f._ 10. _rr._
[494] This insect abounds at East Farleigh, near Maidstone.
[495] Reaum ii. 457.
[496] The insect here alluded to is figured by Olivier under the name
of _Tenebrio nitens_ (No. 57. _t._ i. _f._ 4.): his _Helops æneus_
(No. 58. _t._ i. _f._ 7.) is a different insect.
[497] _Microgr._ 170.
[498] iv. 259.
[499] _Physico-Theol._ Ed. 13. 363, note _b._
[500] _Nat. Hist._ ii. 274.