Salmonia; Or, Days of Fly Fishing / In a series of conversations. With some account of the habits of fishes belonging to the genus Salmo

by Sir Humphry Davy

Hal.—The various individuals of the gryllus, or grasshopper tribe, spring from larvæ, that do not differ much from the perfect insect, except in possessing no wings. The eggs are deposited in our meadows, and many species of this animal are gregarious, and their immigrations in swarms are well known. The butterfly and moths, as you know, lay eggs which produce caterpillars, and these caterpillars, after feeding upon vegetable food, spin themselves or frame houses or beds, cocoons, in which they are transformed into aurelias, and from which they burst forth as perfect winged insects. The libellula, or dragon fly, the most voracious of the winged insect tribe, deposits her eggs in such a manner, that the larvæ fall into the water, and, after destroying and feeding upon almost all the aquatic insects found in this element, and changing their skins at various times, they emerge in their winged form the tyrants of the insect generations in the air. The gnats and tipulæ have a similar existence. The gnat, the female of which only is said by De Geer to bite man, or suck human blood, in Sweden, lays her egg in a kind of little boat or cocoon of her own spinning. These eggs are hatched on the surface of the water, and produce the larvæ, which undergo another change into peculiar nymphæ, that still retain the power of swimming and moving, from which the perfect insect is produced during the summer heat. The flies, which I mentioned to you in a former conversation, under the name of the grannom, or green tail, (see fig. 2,) are of the class phryganeæ, which includes all those water flies that have long antennæ, and wings something like those of moths, but usually veined and without powder. The yellow flies, which you saw a short time since sporting on the banks of the river, are of this kind. The phryganeæ (see fig. 1, 2, 3, and 4,) have four wings, which, when closed, lie flat on their backs, the two upper ones being folded over the lower ones: the flies called by anglers the willow fly, the alder fly, (see fig. 4,) and the dun cut, are of this kind. The phryganeæ lay their eggs on the leaves of willows, or other trees, that overhang the water; they are fastened by a sort of gluten to the surface of the leaf: when hatched, they produce small hexapode larvæ, which fall into the water, and by a curious economy of nature collect round themselves, some, parts of plants, or small sticks; some, gravel; and some, even shell fish. They spin themselves a sort of case of silk from their bodies, and by a gluten, that exudes from this case, cement their materials together. They feed upon aquatic plants, and sometimes upon insects, protruding only their head and legs from the case. When about to undergo transmutation, they quit their cases, rise to the surface, and wait for this process of nature in the air; but some species fix themselves on plants or stones: they burst the skin of the larvæ, and appear perfect animals, male and female, fitted for the office of reproduction. In the early spring, the species which are called green tails, from the colour of the bags of eggs in the female, appear in the warm gleams of sunshine that happen in cloudy days, and they then cover the face of the water, and are greedily seized on by the fish. As the season advances they appear principally in the morning and evening. In the heat of summer the phryganeæ are almost nocturnal flies, and seem to have the habits of moths: at this season, now, I should say, the few flies that appear are generally seen in the day-time. The ephemeræ, another class of flies peculiarly interesting to the fisherman, differ from the phryganeæ in carrying their wings perpendicularly on their backs, and in having long filaments or hairs in their tails. The March brown, (see fig. 8,) the various shades of duns, (see fig. 5, 6, and 7,) which I described to you on a former occasion; the green (see fig. 9 and 10,) and white May fly, the red spinner, (see fig. 11,) are all of the class ephemeræ. These flies are produced from larvæ which inhabit the water, which can both crawl and swim, and which generally live in holes they make in the bottom. They change their coats several times before they become nymphæ. They quit their skin on the surface of the water, but even after they are flies, they have another transformation to undergo before they are perfect animals fitted for generation. They make use of their wings only to fly to some dry bank, or trunk of a tree, where they gradually disencumber themselves of the whole of the outward habiliment they brought from the water, including their wings. They become lighter, more beautiful in colour, and then begin their sports in the sunshine—appearing like what might be imagined of spirits freed from the weight of their terrestrial covering. This last transmutation has been observed and fully described by some celebrated naturalists, in the case of the May flies, and one or two other species, and it probably will be found a general circumstance attached to the class: I have often observed what appeared to me to be the cast-off skins of the small species of ephemeræ on the banks of rivers and floating in the water. The green ephemera, or May fly, lays her eggs sitting on the water, which instantly sink to the bottom: and most of the duns, or small slender-winged flies, do the same. The gray or glossy-winged May fly, commonly called the gray drake, performs regular motions in the air above the water, rising and falling, and sitting, as it were, for a moment on the surface, and rising again, at which time she is said to deposit her eggs. To attempt to describe all the variety of ephemeræ, that sport on the surface of the water at different times of the day, throughout the year, would be quite an endless labour. Some of them appear to live only a few hours, and none of them, I believe, have their existence protracted to more than a few days. In spring and autumn a new variety of these flies sometimes appears every day, or even in different parts of the same day. Of the beetle, or colyoptera genus, there are many varieties fed on by fishes. These insects, which are distinguished, as you know, by four wings, two husky-like shells above, and two slender and finer ones below, are bred from eggs, which they deposit in the ground, or in the excrement of animals, and which, producing larvæ in the usual way, are converted into beetles, and these larvæ themselves are good bait for fish. The brown beetle, or cockchaffer, the fern fly, and the gray beetle, which are abundant in the meadows in the summer, are often blown into the water, and are the most common insects of this kind eaten by fishes. Whether the ditisci and hydrophili, the water beetles, are ever eaten by trout, I know not, but it is most probable. These singular animals are most commonly found in stagnant waters; fitted for flying, swimming, diving, and walking, they are omnivorous, and usually fly from pool to pool in the evening. They deposit their eggs in the water, where their larvæ live, but which, to undergo transmutation into the beetle, migrate to the land. But there is hardly any insect that flies, including the wasp, the hornet, the bee, and the butterfly, that does not become at some time the prey of fishes. I have not, however, the knowledge, or if I had, have not the time, to go through the lists of these interesting little animals; but of the family of one of them I must speak—the ichneumons, that deposit their eggs in caterpillars, or the larvæ of other flies, and which feed on the unfortunate animal in which they are hatched, and come out of its interior when dead, as if it had been their parent. To enter into the philosophy of this subject, and to study the organs and faculties of these various insect tribes, in their functions of respiration, nutrition, and reproduction, would be sufficient for the labour of a life. To know what has already been done would demand the close and studious application of a comprehensive mind; and to complete this branch of science in all its parts is probably almost above human powers: but much might be done if enlightened persons would follow the example of De Geer, Reaumur, and Huber, and study minutely the habits of particular tribes; and it is probable, that physiology might be much advanced by minutely investigating the simplest forms of living beings; and that particularly with respect to the functions of generation a minute study of the modifications of which the forms of animals seems susceptible, particularly in the hymenopterous, or bee tribe, might lead to very important results.

Poiet.—Even in a moral point of view, I think the analogies derived from the transformation of insects admit of some beautiful applications, that have not been neglected by pious entomologists. The three states—of the caterpillar, pupa, or aurelia, and butterfly—have, since the time of the Greek poets, been applied to typify the human being—its terrestrial form, apparent death, and ultimate celestial destination; and it seems more extraordinary that a sordid and crawling worm should become a beautiful and active fly—that an inhabitant of the dark and fœtid dunghill should in an instant entirely change its form, rise into the blue air, and enjoy the sunbeams,—than that a being, whose pursuits here have been after an undying name, and whose purest happiness has been derived from the acquisition of intellectual power and finite knowledge, should rise hereafter into a state of being, where immortality is no longer a name, and ascend to the source of Unbounded Power and Infinite Wisdom.

Phys.—I have been listening, Halieus, to your account of water-flies with attention, and I only regret, that your details were not more copious; let me now call your attention to that Michaelmas daisy. A few minutes ago, before the sun sunk behind the hill, its flowers were covered with varieties of bees, and some wasps, all busy in feeding on its sweets. I never saw a more animated scene of insect enjoyment. The bees were most of them humble bees, but many of them some new varieties to me, and the wasps appeared different from any I have seen before.

Hal.—I believe this is one of the last autumnal flowers that insects of this kind haunt. In sunny days it is their constant point of resort, and it would afford a good opportunity to the entomologist to make a collection of British bees.

Poiet.—I neither hear the hum of the bee, nor can I see any on its flowers. They are now deserted.

Phys.—Since the sun has disappeared, the cool of the evening has, I suppose, driven the little winged plunderers to their homes; but see, there are two or three humble bees which seem languid with the cold, and yet they have their tongues still in the fountain of honey. I believe one of them is actually dead, yet his mouth is still attached to the flower. He has fallen asleep, and probably died whilst making his last meal of ambrosia.

Orn.—What an enviable destiny, quitting life in the moment of enjoyment, following an instinct, the gratification of which has been always pleasurable! so beneficent are all the laws of Divine Wisdom.

Phys.—Like Ornither, I consider the destiny of this insect as desirable, and I cannot help regarding the end of human life as most happy, when terminated under the impulse of some strong energetic feeling, similar in its nature to an instinct. I should not wish to die like Attila in a moment of gross sensual enjoyment: but the death of Epaminondas or Nelson in the arms of victory, their whole attention absorbed in the love of glory and of their country, I think really enviable.

Poiet.—I consider the death of the martyr or the saint as far more enviable; for in this case, what may be considered as a divine instinct of our nature, is called into exertion, and pain is subdued, or destroyed, by a secure faith in the power and mercy of the Divinity. In such cases man rises above mortality, and shows his true intellectual superiority. By intellectual superiority I mean that of his spiritual nature, for I do not consider the results of reason as capable of being compared with those of faith. Reason is often a dead weight in life, destroying feeling, and substituting, for principle, calculation and caution; and, in the hour of death, it often produces fear or despondency, and is rather a bitter draught than nectar or ambrosia in the last meal of life.

Hal.—I agree with Poietes. The higher and more intense the feeling, under which death takes place, the happier it may be esteemed; and I think even Physicus will be of our opinion, when I recollect the conclusion of a conversation in Scotland. The immortal being never can quit life with so much pleasure as with the feeling of immortality secure, and the vision of celestial glory filling the mind, affected by no other passion than the pure and intense love of God.