Cicadas in England—A blower of bubbles—The prolific Aphis—A
nice calculation—Scientific curiosity—Dragon-fly armies—The
son of the south-west wind.
IT is generally understood that there are no cicadas or tettixes in
England, and this—with a reservation in favour of a single species
residing in the New Forest—is roundly asserted in various entomological
works of authority. Since, however, Mr. George Bowdler Buckton, F.R.S.,
has written a monograph of the British _Cicadæ_, or _Tettigidæ_, in two
volumes, each of which has a number of plates giving figures of the
various species, all with their Latin names, there would seem to be a
conflict of learned opinion; and I, for my part—since one of these
species has relations with a nice little parasite which I should like to
describe—am of opinion, after profound investigation and impartial
weighing of the evidence on both sides, that Mr. Buckton is right. What
strikes one at first sight as curious is that numbers of creatures, as
large sometimes as humble bees, or larger, and of very striking
appearance—often quite brilliantly coloured—should for so long have
escaped observation; for certainly one has never seen them oneself, and,
on making inquiries, one soon finds that nobody else has. But there is
an explanation of this seeming miracle, and that of a not very
satisfactory nature. One may have noticed, whilst going through the
plates, that in the neighbourhood of each striking figure there are two
little irrelevant-looking black lines, drawn soft and fine, very
unobtrusive, looking as though they wished to elude observation; and
gradually it begins to dawn upon you that these lines represent the real
size in linear measurement of the very salient, _outré_-looking creature
you are looking at. This, then, is the key to the mystery. England is
full of cicadas, but they are all so small that nobody can see them—at
least without taking some trouble. So our poets have been silent, our
philosophers have made no reflections, and our ploughmen, to this day,
are without a proper objective for those appreciative perceptions of
life around them which, if it only existed, there might be some evidence
of their possessing. Our aristocracy too, or old county families, have
never been able to “think gold of themselves,” as the saying is, on
account of their golden tettix-pins, though the feeling itself has not
been entirely denied them. In a word, our national character has been
uninfluenced by cicadas, and, on this, two questions arise: first—for it
is no use to start on an assumption—whether faults exist in it, and
then, if they do, whether all or any of them are due to this cause. But
such matters are for the historian to deal with, and would be out of
place in the pages of a work like this.
Though cicadas are so small in England—whilst their voices, if they have
any, as there seems no particular reason to doubt, are too attenuated to
be audible to our human ears—yet they are not quite invisible. When
seen, however, they are known by some other name, such as frog-hoppers,
tree-hoppers, or the like. Some of these, in their larval stage, which
much resembles the adult, take a great deal of pains to conceal
themselves, though in this they have another reason than that of wishing
to elude observation. Our common cuckoo-spit is a good instance of this,
and also of how a wrong explanation of a common and easily observed
phenomenon may for a long time be given, not only in popular works, but
also in scientific text-books or monographs, or within the supposedly
up-to-date pages of various encyclopædias. The cuckoo-spit, as everyone
knows, sits in the midst of a little bower of froth (allied to that
other of bliss perhaps) which, on being examined, resolves itself into
an accumulation of bubbles, having a somewhat sticky consistency. We had
always been told—and still are now very often, though the contrary has
been well made out—that these bubbles proceeded from the insect itself,
after the manner of any other secretion. But this is not the case. The
secretion here is only a clear fluid, and into this the insect
afterwards blows bubbles by a mechanical process, and through the
addition of air. It is Professor E. S. Morse who, in the pages of
_Appleton’s Popular Scientific Monthly_,[35] has thus revolutionised all
our ideas on this subject. His account is as follows: “The so-called
frog-spittle or cuckoo-spit appears as little flecks of froth on grass,
buttercups, and many other plants during the early summer. Immersed in
this froth is found a little green insect, sometimes two or three of
them concealed by the same moist covering. This little creature
represents the early stage of an insect which, in its full growth, still
lives upon grass, and is easily recognised by its triangular shape and
its ability of jumping like a grasshopper.”
“If the insect is cleared from the mass of froth it will crawl quite
rapidly along the stem of the plant, stopping, at times, to pierce the
stem for the purpose of sucking the juices within, and finally settling
down in earnest, clutching the stem with its legs. After sucking for
some time, a clear fluid is seen to exude from the end of the abdomen,
flowing over the body first, and gradually filling up the spaces between
the legs and the lower part of the body and the stem upon which it
rests. During all this time not a trace of an air-bubble appears; simply
a clear, slightly viscid fluid is exuded, and this is the only matter
that escapes from the insect. This state of partial immersion continues
for an hour or more. During this time, and even when walking, the
posterior segments of the insect’s abdomen are extended at intervals,
the abdomen turning upwards at the same time. It is a kind of
reaching-up movement, but whether this action accompanies a discharge of
fluid, or is an attempt at reaching for air, I have not ascertained.
Suddenly the insect begins to make bubbles by turning its tail out of
the fluid, opening the posterior segment, and grasping, as with a pair
of claspers, a moiety of air, then turning the tail down into the fluid,
again, and instantly allowing the enclosed air to escape. These
movements go on at the rate of seventy or eighty times a minute. The
tail is moved alternately to the right and left in perfect rhythm, so
that the bubbles are distributed on both sides of the body, and these
are crowded towards the head, till the entire fluid is filled with
bubbles, and the froth thus made runs over the back and around the stem.
In half a minute some thirty or forty bubbles are made in this way—a
bulk of air two or three times exceeding that of the body—without the
slightest diminution in the size of the body.”
It seems clear, therefore, that the air which is put to this purpose is
abstracted directly from the atmosphere, and that neither it nor the
bubbles manufactured through it have ever been within the body of the
insect. Moreover, if the little bubble-maker be thoroughly dried—which,
according to Professor Morse, is a matter of difficulty—it will continue
to secrete such spare fluid as it still has, but not the tiniest bubble
is seen to issue with this. If set in a drop of water it struggles to
the surface, and then goes through the same process of blowing bubbles
as it has done when immersed in fluid of its own distilling. The result,
however, is not the same, for the water will not hold the bubbles, which
constantly disappear. Such, then, is the manner in which the frothy pool
is made. What purposes does it answer? That of a pond, apparently, for
it would appear that in their larval state these little frog-, or
tree-hoppers, are to some extent aquatic insects. If kept dry and not
allowed to renew their supply of fluid, their body shrivels, and before
long they die. This is not through suffocation, since they can breathe
air, by means of spiracles, in the ordinary way. If, however, they are
examined closely, certain leaf-like appendages may be detected upon each
side of the seventh and eighth segments of the abdomen, and Professor
Morse suggests that these may be of the nature of branchiæ, or gills,
enabling the insect to breathe, also, in water or fluid, by abstracting
the air from it, after the manner of a fish, as some other aquatic larvæ
do. “As many of these,” he says, “respire in two ways, either inhaling
air through the spiracles, or by means of branchial leaflets, so
_Aphrophora_ (for that is the classic name of our insect) may likewise
utilise its branchial tufts for the same purpose. Thus we may see the
reason for this bubble-blowing, since each fresh bubble added to the
mass may aerate the fluid, so to speak, and thus secure at intervals a
fresh supply of oxygen.”[36]
In early spring, if one examines the leaf-buds of rose trees, which now
begin to swell, one may often see tiny little black specks, like grains
of gunpowder, scattered over their surface, especially within any fold
or crevice which it presents. These are the eggs of the Aphides, insects
which, if not cicadas, are not so very far removed from them, and which,
looked at from various points of view, are extremely interesting little
creatures. One of these points of view, which we may conveniently start
from, is their extraordinary rate of increase, which exceeds even that
of the Chinese. “A single insect,” says Mr. Buckton, “hatched from one
of these shining black ova may be the mother of many billions of young,
even during her lifetime. Réaumur calculated that one Aphis may be the
mother of the enormous number of 5,904,900,000 individuals during the
month or six weeks of her existence. But neither Tongard nor Morren is
satisfied with this estimate, both declaring that quintillions are
within the capabilities of a single mother’s efforts. Professor Huxley
(who, by the way, was not interested in the alleged phenomena of
spiritualism, _even if true_) makes a curious calculation which, at any
rate, affords some approximate idea of what a quintillion of Aphides
might mean. Assuming that an Aphis weighs as little as one-thousandth of
a grain (which is less than I should ever have thought), and that it
requires a man to be very stout to weigh more than two million grains,
he shows that the tenth brood of Aphides alone, without adding the
product of all the generations which precede the tenth, if all the
members survive the perils to which they are exposed, contains more
ponderable substance than 500,000,000 of stout men: that is, more than
the whole population of China.”[37] This, it appears, is an
under-estimate, which is rather annoying, for one would like to call it
a gross exaggeration. But facts are facts—in whatever degree they may
interest one—and it is impossible not to feel respect for an insect like
this, especially in these days, when the diminished returns of the
census are beginning to cause alarm as to the future destinies even of
our own once proudly fecund race. It is a wonderful record for a single
individual—to have weighed down China—and when Mr. Buckton remarks that
facts like these regarding the prolific nature of Aphides “afford
sufficient explanation of the occurrence of the extraordinary swarms so
often noticed by authors,”[37] nobody is likely to disagree with him.
With billions a certainty, and quintillions in the air, swarms seem
amply accounted for.
One of the authors here alluded to is our homely immortal, White of
Selborne. “I shall here mention,” he says, “an emigration of small
Aphides, which was observed in the village of Selborne no longer ago
than August 1st, 1785. At about three o’clock in the afternoon of that
day, which was very hot, the people of this village were surprised by a
shower of Aphides, or smother-flies, which fell in these parts. Those
that were walking in the streets at that juncture found themselves
covered with these insects, which settled, also, on the hedges and
gardens, blackening all the vegetables where they alighted. My annuals
were discoloured with them, and the stalks of a bed of onions were quite
coated over for six days after. These armies were then, no doubt, in a
state of emigration and shifting their quarters; and might have come, as
far as we know, from the great hop-plantations of Kent or Sussex, the
wind being, all that day, in the easterly quarter. They were observed,
at the same time, in great clouds about Farnham, and all along the vale
from Farnham to Alton.”[38]
Other great migrations of Aphides have at various times been observed.
In the autumn of 1834 the city of Gand was invaded, and, one may almost
say, taken by a vast army of them, and at Bruges and Antwerp the same
swarm is said to have darkened the sun,[39] a result of such gatherings
more noticeable elsewhere than in England, since our sun usually is
darkened. Insects, though their movements are not so regular, nor, as a
rule, so noticeable as those of birds, yet often migrate—how often or
how regularly it is difficult to say. Locusts are, of course, the stock
example as well as the most terrific one, but perhaps dragon-flies, were
they as destructive, would have been as much noted in this connexion.
Their migrations seem to be tolerably frequent, and a record of them
between 1494 and 1868 has been published by Koppen, a German
entomologist. In 1881 a great flight of them took place in Illinois.
“The air,” we are told, “for miles around seemed literally alive with
these dragon-flies, from a foot above ground to as far as eye could
reach, all flying in the same direction, a south-westerly course, and
the few that would occasionally cross the track of the majority could
all the more easily be noticed from the very regular and swift course
they generally pursued; but even these few stray ones would soon fall in
with the rest again. Very few were seen alighting and all carefully
avoided any movable obstacles.”[40] This migration took place during a
very dry season, and may have been caused by it owing to the drying up
of swamps, ponds, etc., in which the insects would otherwise have laid
their eggs, obliging them to seek other suitable places.
In the spring of 1900 a great migration of dragon-flies was observed in
Belgium. “All the observers agree that the insects flew rather low, with
astonishing regularity, and without resting; that they kept close to the
earth, where there were no obstacles, but that they mounted to a height
of 10 to 12 mètres when houses or trees were in the way. They did not go
round obstacles in their line of route, but surmounted them, and
descended on the other side. According to some observers, their flight
was very slow, others again asserting that it was very swift. When the
velocity could be estimated, however, it was found to be at 5 mètres per
second or 18 kilometres (11¼ miles) per hour (so that the slows have
it). In general they went in groups, more or less isolated, and more or
less dense.” The writer of the above account—a Belgian—concludes thus:
“All the facts point to the following conclusions: The dragon-flies of
the 5th came from regions situated to the east of the country, which
they entered in several columns, flying at a great altitude: between 7
and 8 a.m. they descended towards the earth, continuing their route
towards the west. But we remain in ignorance of their point of
departure. The swarm probably quitted its usual habitation early in the
morning, and immediately flew to a great height. It was only on arriving
near the earth that they flew against the wind”[41] (which, however,
they then continued to do).
What Mr. Hudson calls “dragon-fly storms” are a special phenomenon of
the Pampas. In this case the cause of the migration—for such movements
seem to come under this heading—is a special wind called the _pampero_,
that blows south-west from the interior of the Pampas. It is very
violent, cold, and dry, and the dragon-flies evidently fear it. The
“storm” is thus described by Mr. Hudson: “It is in summer and autumn
that the large dragon-flies appear; not _with_ the wind, but—and this is
the most curious part of the matter—in advance of it; and inasmuch as
these insects are not seen in the country at other times, and frequently
appear in seasons of prolonged drought, when all the marshes and
watercourses for many hundreds of miles are dry, they must, of course,
traverse immense distances, flying before the wind at a speed of 70 or
80 miles an hour. On some occasions they appear almost simultaneously
with the wind, going by like a flash, and instantly disappearing from
sight. You have scarcely time to see them before the wind strikes you.
As a rule, however, they make their appearance from 5 to 15 minutes
before the wind strikes; and when they are in great numbers, the air, to
a height of 10 or 12 feet above the surface of the ground, is all at
once seen to be full of them, rushing past with extraordinary velocity
in a north-easterly direction. In very oppressive weather, and when the
swiftly advancing _pampero_ brings no moving mountains of mingled cloud
and dust, and is, consequently, not expected, the sudden apparition of
the dragon-fly is a most welcome one, for then an immediate burst of
cold wind is confidently looked for. In the expressive vernacular of the
gauchos the large dragon-fly is called ‘_hijo del pampero_,’ son of the
south-west wind.”[42]
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Footnote 35:
Vol. 57.
Footnote 36:
Appleton’s Popular Scientific Monthly, vol. v.
Footnote 37:
Buckton, Monograph of the British Cicadæ or Tettigidæ.
Footnote 38:
White’s Natural History of Selborne, Letter liii. p. 283 (stereotyped
edition).
Footnote 39:
Buckton, Monograph of the British Cicadæ or Tettigidæ.
Footnote 40:
Leland O. Howard, The Insect Book.
Footnote 41:
The Entomologist’s Monthly Magazine, October, 1900.
Footnote 42:
Hudson, The Naturalist in La Plata, pp. 131, 32.
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