"Nor wanting here to entertain the thought,
Creatures that in communities exist,
Less, as might seem, for general guardianship
Or through dependance upon mutual aid,
Than by participation of delight,
And a strict love of fellowship combined.
What other spirit can it be that prompts
The gilded summer flies to mix and weave
Their sports together in the solar beam,
Or in the gloom and twilight hum their joy?"
Another association is that of males during the season of pairing. Of this nature seems to be that of the cockchafer and fernchafer (Melolontha vulgaris and Amphimalla solstitialis), which, at certain periods of the year and hours of the day, hover over the summits of the trees and hedges like swarms of bees, affording, when they alight on the ground, a grateful food to cats, pigs, and poultry. The males of another root-devouring beetle (Hoplia argentea) assemble by myriads before noon in the meadows, when in these infinite hosts you will not find even one female[3]. After noon the congregation is dissolved, and not a single individual is to be seen in the air[4]: while those of M. vulgaris and A. solstitialis are on the wing only in the evening.
At the same time of the day some of the short-lived Ephemeræ assemble in numerous troops, and keep rising and falling alternately in the air, so as to exhibit a very amusing scene. Many of these also are males. They continue this dance from about an hour before sun-set, till the dew becomes too heavy or too cold for them. In the beginning of September, for two successive years, I was so fortunate as to witness a spectacle of this kind, which afforded me a more sublime gratification than any work or exhibition of art has power to communicate.—The first was in 1811:—taking an evening walk near my house, when the sun declining fast towards the horizon shone forth without a cloud, the whole atmosphere over and near the stream swarmed with infinite myriads of Ephemeræ and little gnats of the genus Chironomus, which in the sun-beam appeared as numerous and more lucid than the drops of rain, as if the heavens were showering down brilliant gems.—Afterwards, in the following year, one Sunday, a little before sun-set, I was enjoying a stroll with a friend at a greater distance from the river, when in a field by the road-side the same pleasing scene was renewed, but in a style of still greater magnificence; for, from some cause in the atmosphere, the insects at a distance looked much larger than they really were. The choral dances consisted principally of Ephemeræ, but there were also some of Chironomi; the former, however, being most conspicuous, attracted our chief attention—alternately rising and falling, in the full beam they appeared so transparent and glorious, that they scarcely resembled any thing material—they reminded us of angels and glorified spirits drinking life and joy in the effulgence of the Divine favour[5]. The bard of Twickenham, from the terms in which his beautiful description of his sylphs is conceived in The Rape of the Lock, seems to have witnessed the pleasing scene here described:
"Some to the sun their insect wings unfold,
Waft on the breeze, or sink in clouds of gold;
Transparent forms, too fine for mortal sight,
Their fluid bodies half dissolv'd in light;
Loose to the wind their airy garments flew,
Thin glittering textures of the filmy dew,
Dipt in the richest tincture of the skies,
Where light disports in ever mingling dyes,
While every beam new transient colours flings,
Colours that change whene'er they wave their wings."
I wish you may have the good fortune next year to be a spectator of this all but celestial dance. In the mean time, in May and June, their season of love, you may often receive much gratification from observing the motions of a countless host of little black flies of the genus Hilara, (H. maura,) which at this period of the year assemble to wheel in aëry circles over stagnant waters, with a rush resembling that of a hasty shower driven by the wind.
The next description of insect associations is of those that congregate for the purpose of travelling or emigrating together. De Geer has given an account of the larvæ of certain gnats (Tipulariæ) which assemble in considerable numbers for this purpose, so as to form a band of a finger's breadth, and of from one to two yards in length. And, what is remarkable, while upon their march, which is very slow, they adhere to each other by a kind of glutinous secretion; but when disturbed they separate without difficulty[6]. Kuhn mentions another of the same tribe (from the antennæ in his figure, which is very indifferent, it should seem a species of agaric-gnat (Mycetophila)), the larvæ of which live in society and emigrate in files, like the caterpillar of the procession-moth. First goes one, next follow two, then three, &c., so as to exhibit a serpentine appearance, probably from their simultaneous undulating motion and the continuity of the files; whence the common people in Germany call them (or rather the file when on march) heerwurm, and view them with great dread, regarding them as ominous of war. These larvæ are apodes, white, subtransparent, with black heads[7].—But of insect emigrants none are more celebrated than the locusts, which, when arrived at their perfect state, assemble as before related, in such numbers, as in their flight to intercept the sunbeams, and to darken whole countries; passing from one region to another, and laying waste kingdom after kingdom:—but upon these I have already said much, and shall have occasion again to enlarge.—The same tendency to shift their quarters has been observed in our little indigenous devourers, the Aphides. Mr. White tells us, that about three o'clock in the afternoon of the first of August 1785, the people of the village of Selborne were surprised by a shower of Aphides or smother-flies, which fell in those parts. Those that walked in the street at that juncture found themselves covered with these insects, which settled also upon the hedges and in the gardens, blackening all the vegetables where they alighted. His annuals were discoloured by them, and the stalks of a bed of onions quite coated over for six days after. These armies, he observes, were then, no doubt, in a state of emigration, and shifting their quarters; and might have come from the great hop-plantations of Kent or Sussex, the wind being all that day in the east. They were observed at the same time in great clouds about Farnham, and all along the vale from Farnham to Alton[8]. A similar emigration of these flies I once witnessed, to my great annoyance, when travelling later in the year, in the Isle of Ely. The air was so full of them, that they were incessantly flying into my eyes, nostrils, &c.; and my clothes were covered by them. And in 1814, in the autumn, the Aphides were so abundant for a few days in the vicinity of Ipswich, as to be noticed with surprise by the most incurious observers.
As the locust-eating thrush (Turdus gryllivorus) accompanies the locusts, so the lady-birds (Coccinellæ) seem to pursue the Aphides; for I know no other reason to assign for the vast number that are sometimes, especially in the autumn, to be met with on the sea-coast or the banks of large rivers. Many years ago, those of the Humber were so thickly strewed with the common Lady-bird (C. septempunctata), that it was difficult to avoid treading upon them. Some years afterwards I noticed a mixture of species, collected in vast numbers, on the sand-hills on the sea-shore, at the north-west extremity of Norfolk. My friend the Rev. Peter Lathbury made long since a similar observation at Orford, on the Suffolk coast; and about five or six years ago they covered the cliffs, as I have before remarked[9], of all the watering-places on the Kentish and Sussex coasts, to the no small alarm of the superstitious, who thought them forerunners of some direful evil. These last probably emigrated with the Aphides from the hop-grounds. Whether the latter and their devourers cross the sea has not been ascertained; that the Coccinellæ attempt it, is evident from their alighting upon ships at sea, as I have witnessed myself.—This appears clearly to have been the case with another emigrating insect, the saw-fly (Athalia?) of the turnip (which, though so mischievous, appears never to have been described; it is nearly related to A. Centifoliæ)[10]. It is the general opinion in Norfolk, Mr. Marshall informs us[11], that these insects come from over sea. A farmer declared he saw them arrive in clouds so as to darken the air; the fishermen asserted that they had repeatedly seen flights of them pass over their heads when they were at a distance from land; and on the beach and cliffs they were in such quantities, that they might have been taken up by shovels-full. Three miles in-land they were described as resembling swarms of bees. This was in August 1782. Unentomological observers, such as farmers and fishermen, might easily mistake one kind of insect for another; but supposing them correct, the swarms in question might perhaps have passed from Lincolnshire to Norfolk.—Meinecken tells us, that he once saw in a village in Anhalt, on a clear day, about four in the afternoon, such a cloud of dragon-flies (Libellulina) as almost concealed the sun, and not a little alarmed the villagers, under the idea that they were locusts[12]: several instances are given by Rösel of similar clouds of these insects having been seen in Silesia and other districts[13]; and Mr. Woolnough of Hollesley in Suffolk, a most attentive observer of nature, once witnessed such an army of the smaller dragon-flies (Agrion) flying in-land from the sea, as to cast a slight shadow over a field of four acres as they passed.—Professor Walch states, that one night about eleven o'clock, sitting in his study, his attention was attracted by what seemed the pelting of hail against his window, which surprising him by its long continuance, he opened the window, and found the noise was occasioned by a flight of the froth frog-hopper (Cercopis spumaria), which entered the room in such numbers as to cover the table. From this circumstance and the continuance of the pelting, which lasted at least half an hour, an idea may be formed of the vast host of this insect passing over. It passed from east to west; and as his window faced the south, they only glanced against it obliquely[14]. He afterwards witnessed, in August, a similar emigration of myriads of a kind of ground-beetle (Amara vulgaris,)[15].—Another writer in the same work, H. Kapp, observed on a calm sunny day a prodigious flight of the noxious cabbage-butterfly (Pontia Brassicæ), which passed from north-east to south-west, and lasted two hours[16]. Kalm saw these last insects midway in the British Channel[17]. Lindley, a writer in the Royal Military Chronicle, tells us, that in Brazil, in the beginning of March 1803, for many days successively there was an immense flight of white and yellow butterflies, probably of the same tribe as the cabbage-butterfly. They were observed never to settle, but proceeded in a direction from north-west to south-east. No buildings seemed to stop them from steadily pursuing their course; which being to the ocean, at only a small distance, they must consequently perish. It is remarked that at this time no other kind of butterfly is to be seen, though the country usually abounds in such a variety[18].—Major Moor, while stationed at Bombay, as he was playing at chess one evening with a friend in Old Woman's Island, near that place, witnessed an immense flight of bugs (Geocorisæ), which were going westward. They were so numerous as to cover every thing in the apartment in which he was sitting.—When staying at Aldeburgh, on the eastern coast, I have, at certain times, seen innumerable insects upon the beach close to the waves, and apparently washed up by them. Though wetted, they were quite alive. It is remarkable, that of the emigrating insects here enumerated, the majority—for instance the lady-birds, saw-flies, dragon-flies, ground-beetles, frog-hoppers, &c.—are not usually social insects, but seem to congregate, like swallows, merely for the purpose of emigration. What incites them to this is one of those mysteries of nature, which at present we cannot penetrate. A scarcity of food urges the locusts to shift their quarters; and too confined a space to accommodate their numbers occasions the bees to swarm: but neither of these motives can operate in causing unsocial insects to congregate. It is still more difficult to account for the impulse that urges these creatures, with their filmy wings and fragile form, to attempt to cross the ocean, and expose themselves, one would think, to inevitable destruction. Yet, though we are unable to assign the cause of this singular instinct, some of the reasons which induced the Creator to endow them with it may be conjectured. This is clearly one of the modes by which their numbers are kept within due limits, as, doubtless, the great majority of these adventurers perish in the waters. Thus, also, a great supply of food is furnished to those fish in the sea itself, which at other seasons ascend the rivers in search of them; and this probably is one of the means, if not the only one, to which the numerous islands of this globe are indebted for their insect population. Whether the insects I observed upon the beach wetted by the waves, had flown from our own shores, and falling into the water had been brought back by the tide; or whether they had succeeded in the attempt to pass from the continent to us, by flying as far as they could, and then falling had been brought by the waves, cannot certainly be ascertained; but Kalm's observation inclines me to the latter opinion.
The next order of imperfect associations is that of those insects which feed together:—these are of two descriptions—those that associate in their first or last state only, and those that associate in all their states. The first of these associations is often very short-lived: a patch of eggs is glued to a leaf; when hatched, the little larvæ feed side by side very amicably, and a pleasant sight it is to see the regularity with which this work is often done, as if by word of command; but when the leaf that served for their cradle is consumed, their society is dissolved, and each goes where he can to seek his own fortune, regardless of the fate or lot of his brethren. Of this kind are the larvæ of the saw-fly of the gooseberry, whose ravages I have recorded before[19], and that of the cabbage-butterfly; the latter, however, keep longer together, and seldom wholly separate. In their final state, I have noticed that the individuals of Thrips Physapus, the fly that causes us in hot weather such intolerable titillation, are very fond of each other's company when they feed. Towards the latter end of last July, walking through a wheat-field, I observed that all the blossoms of Convolvulus arvensis, though very numerous, were interiorly turned quite black by the infinite number of these insects, which were coursing about within them.
But the most interesting insects of this order are those which associate in all their states.—Two populous tribes, the great devastators of the vegetable world, the one in warm and the other in cold climates, to which I have already alluded under the head of emigrations—you perceive I am speaking of Aphides and Locusts—are the best examples of this order: although, concerning the societies of the first, at present we can only say that they are merely the result of a common origin and station: but those of the latter, the locusts, wear more the appearance of design, and of being produced by the social principle.