THE EPHEMERA. 



485 



however, though so formidable to others, are 

 nevertheless themselves greatly overrun with 

 a little kind of louse, about the size of a nit, 

 which very probably repays the injury which 

 the water-scorpion inflicts upon others. 



The water-scorpions live in the water by 

 day : out of which they rise, in the dusk of 

 the evening, into the air, and so flying from 

 place to place often betake themselves, in quest 

 of food, to other waters. The insect, before 

 its wings are grown, remains in the place 

 where it was produced; but when come to its 

 state of perfection, sallies forth in search of a 

 companion of the other sex, in order to conti- 

 nue its noxious posterity. 



CHAP. VI. 



OF THE EPHEMERA. 1 



THE last insect we shall add to the second 

 order is the Ephemera; which, though not 



1 Ephemera. There are many species of these in- 

 sects, some larger and some smaller, some longer-lived 

 and some shorter, but as few of them live to behold the 

 rising and the setting sun, they are all called ephemera, 

 or "things of a clay," their name is used to express all 

 things that are very fleeting. 



In autumn any one who walks by the water-side when 

 the air is still, especially towards morning or evening, 

 may catch them by thousands. They have four-wings, of 

 a beautiful transparent membrane or film, spread out 

 upon a fine net- work, of a substance very similar to horn. 

 These fibres in the wings are called nerves, and the in- 

 sects which have such wings are by naturalists called 

 neuroptera, which is the Greek for "nerve-winged ;" but 

 these are not nerves. Nerves are understood to be or- 

 gans of feeling or sensation ; whereas, the fibres in the 

 wings of those insects, merely support the membrane, just 

 as the arm-frames of a windmill, or the masts and yards 

 of a ship, support the canvas. 



The eggs of the day-flies are all laid in the water, and 

 hatched there ; so that they so far partake of the nature 

 of the eggs, or race of fishes, that they " come into ac- 

 tive life," in less heat than land eggs, and do not need 

 any incubation, or sitting, of the mother. Each female 

 lays from 700 to 800, and she does it in less time than it 

 takes to speak the words. The eggs are expelled in two 

 portions, one of each at a time; but so fast, that the eggs 

 seem two little knotted rods ; but they separate and sink 

 to the bottom undiscovered by the keen eyes of the fish. 

 The female instantly dies, exhausted by the effort, which 

 appears to be the only labour of her winged state of exis- 

 tence ; if, indeed, she is not captured in the midst of her 

 maternal duty by some darting fish, or skimming swal- 

 low; both of which prey upon countless thousands of the 

 day-flies. When the fly lights to deposit her eggs, she 

 raises her wings over her back, till they are nearly touch- 

 ing; and, at the same time, she elevates the hinder part 

 of her body, and erects the three setae, or bristles, in 

 which it terminates. The wings and these bristles sup- 

 port her so that she barely touches the water, and so rises 

 and falls with the ripple. 



The moment that the females are in a condition to lay 

 their eggs, they hasten to the waters, so that they are not 



strictly belonging to it, yet seems more pro 

 perly referred to this rank than any other. In- 

 deed, we must not attend to the rigour of me- 

 thod in a history where Nature seems to take 

 delight to sport in variety. 



That there should be a tribe of flies whose 

 duration extends but to a day, seems, at first, 

 surprising ; but the wonder will increase, when 

 we are told, that some of this kind seem to be 

 born and to die in a space of a single hour. 

 The reptile, however, from which they are 

 bred, is by no means so short-lived; but is 

 sometimes seen to live two years, and many 

 times three years together. 



All ephemeras, of which there are various 



so often seen as the males, whose only occupation is to 

 sport in the air, in the neighbourhood of the cradle of 

 their future offspring. Of these the little day-fly, which 

 is born after dawn, produces her eight hundred, and is 

 dead and gone, before the first gleam of the sun breaks 

 over the eastern hill ! 



How long the eggs remain in the water before they 

 are hatched, is not known; but possibly it varies with the 

 season and the weather. The larva or young, in their 

 first state, not only burrow, or make holes in the mud, 

 but live on it; they are consequently not so numerous in 

 sand and gravel as in places that are fat and oozy. 



In summer the ponds, brooks, and ditches, are full of 

 these larvae, and so are water tanks, cisterns, and butts, 

 if they are not kept clean. They (with the larvae of 

 other species) are among the chief summer impurities in 

 the water at London and other places. If the water is 

 not settled, they may come from the river; but the mud 

 and sediment will enable them to breed in vessels, and 

 the parent flies are every where. In themselves they are 

 not unwholesome, and, as they are alive, they cannot 

 render the water putrid. The mud that breeds them, is 

 putrid, however, as it contains dead animal and vegetable 

 matter; and thus, though the young flies are not in them- 

 selves unwholesome, they are accompanied by substances 

 that are so. 



The larvae remain in the mud two or three years ; but 

 in that they probably vary. The banks of rivers, in some 

 parts of the continent, are so full of them, that to the 

 depth of some inches, they actually contain more living 

 matter than dead. They are all, however, lower than 

 the surface of the water, and they breathe water, like 

 fishes, by means of little gills on their sides. At length 

 they attain their full size, and change into nymphte, 

 which are not unlike the larvae, only they have wings 

 folded up under their coats, of which they still have 

 two, and must get out of both before they appear as flies. 



The time that they remain nymphs is uncertain, and 

 must vary, as the weather is one element in bringing 

 about their last change. When that is to take place, 

 they come out of the water, in vast numbers, and leave 

 their old coats so abundant as to cover the water like a 

 scum. After a little while they cast their inner coat ; 

 their wings stretch and become firm, and they mount into 

 the air, to spend the hour, or the day, which is to them 

 the whole period of air-breathing life. 



That period is short; but that is necessary: for, in 

 some places, if they were to live long, there would abso- 

 lutely not be room for them. They eat nothing, and so 

 destroy nothing; but there are places in France and 

 Germany where, if they lived but for a month on the 

 wing, they would build up the air solid to the tops of the 

 trees. As it is, they sometimes fall on the ground near 

 the rivers in showers like snow, and the people collect 

 them in heaps as manure to the fields. 



