Imágenes de páginas
PDF
EPUB

fly, and viewed the steeple of a church which was 299 feet high, and 750 from the place where he stood. He could plainly see the steeple, though not apparently larger than the point of a fine needle. He also viewed a house in the same manner, and could discern the front, distinguish the doors and windows, and perceive whether they were open or shut !-pp 123–129.

With reference to the means of providing themselves with food, insects are divided into eaters, lappers, and suckers; they are, many of them, in their way, very destructive to fruits and vegetables, as the gardeners have too much reason to know. Of late years our apple trees have suffered extensively from what is called the American, or white blight, which, according to Mr. Knapp, was first observed in 1819, in nursery gardens near Bristol, and is supposed to have been introduced by some imported plant. There are others who say that it originally came over from France with the Hugonot exiles in the reign of Louis XIV.; there is no doubt that it is well known in that country. This blight first appears in the spring of the year in the form of a slight hoariness, which is observed upon the branches of certain species of our orchard fruit. In the course of a few weeks the hoariness increases, becomes cottony, and as the summer advances it grows into a downy substance, which upon examination is found to conceal a multitude of small wingless creatures, busily employed in consuming what we may well call the life-blood of the plant. They are possessed of a beak, terminating in a fine bristle, which they insinuate through the bark and the sappy part of the wood, and thus they are enabled to extract, as with a syringe, the sweet vital liquor that circulates in the plant. The consequence is, that the limb grows sickly, the leaves fall off, and branch after branch being thus attacked, the whole tree gradually dies.

The garden and house bugs form another part of the destructive families of imported insects. It is said that they were not known in England until about the period of the discovery of America, which countenances the opinion of Linnæus, that they were brought hither from that continent. Mr. Rennie says he never saw the house bug in Ireland. He must have been very lucky, or must never have been in Dublin, where they abound quite as much as in London. Mr. Brande has recommended the following poison for their destruction:-“Reducean ounce of corrosive sublimate (Perchloride of Mercury) and one ounce of white arsenic, to a fine powder ; mix with it one ounce of muriate of ammonia in powder, two ounces each of oil of turpentine and yellow wax, and eight ounces of olive oil; put all these into a pipkin, placed in a pan of boiling water, and when the wax is melted, stir the whole, till cold, in a mortar.”

The history of the pairing of insects furnishes Mr. Rennie with the materials of a long and interesting chapter, in the course of which he shews pretty clearly that insects do not unite after the manner of birds and other animals, upon the principle of mutual

assistance in rearing their progeny. Indeed it does not appear that the male insect renders any assistance whatever to the female, except in the instance of the solitary bee, nor does he help to construct the nest, but he defends it with great vigour from the intrusion of enemies. In the instance of carnivorous insects, the sexes often attack and devour each other, and the females, being the larger and more powerful of the two, usually are the conquerors. The female spider has been sometimes seen to wrap her mate in the very toils in which he perhaps was waiting to catch a fly, and to feed upon him without any ceremony. The male spider is easily known by a sort of knob at the extremities of the feelers, which is wanting in the female. It is an extraordinary fact, that after insects pair, and the females deposit their eggs, they very soon die, seldom surviving more than a few days at the utmost. If pairing be prevented, their lives may be protracted to an indefinite period.

Mr. Rennie discusses, at some length, the question, interesting in a poetical as well as a natural point of view, whether the light of the female glow-worm be intended as a lamp to attract the attention of the male; “ the lamp of love,” as Dumeril calls it, which in the words of another writer, “the wingless female, doomed to crawl upon the grass, lights up at the approach of night, as a beacon which unerringly guides the vagrant male to her love-illumined form, however obscure the place of her abode.” It is supposed to be rather unfortunate for this beautiful theory, that the insect has been found to shine in its infant state, in that of larva, and even after it has taken the form of a nymph, stages of its existence in which it has just as little to do with love as a baby. It has also been ascertained that the male has a lamp of his own, which though not quite so brilliant as that of the female, is still bright enough to be perceptible. Nevertheless, we are not disposed to give up the theory in question ; since, as Mr. Rennie admits, the light afforded by the larva may be easily explained upon the principle of gradual development, and with respect to the feeble glimmering observable in the male, it may be reasonably supposed to originate in the possession of some organs common to the whole species. He imagines that he has put an extinguisher upon the question, by an experiment which he made at Hâvre de Grace, where, having collected some female glow worms in a box, he went about one evening until midnight with his box in his hand, to see if he could not attract a male towards them, and he failed. This surely is no negative proof by itself, for it might be that the males were repelled by the concentrated blaze' which was thus created, and that like other lovers they prefer solitude and the shade. Besides, according to all accounts, the male is exceedingly scarce in proportion to the number of the other sex. Mr. Rennie says he never found but one, and Mr. Knapp, to whom we are indebted for that delightful book, the Journal of a Naturalist, informs us that

he seldom met with more than one in a year. It is well ascertained that the little creature ceases to shine about midnight, thus justifying the well-known lines of Shakspeare :

“ The glow-worm shows the matin to be near,

And 'gins to pale his ineffectual fire.” The bard had not taken the trouble to ascertain the sex of his insect; and from the epithet “ineffectual” it would seem that he held the opinion now maintained by Mr. Rennie, that the light serves no purpose at all. The only other luminous insect met with in this country, is the electric centipede, though from living in the ground its light is seldom seen. It may, however, be sometimes traced by a track of phosphoric matter, which it leaves behind it. This subject leads the author to some remarks upon that beautiful phenomenon of the sparkling light, so frequently seen at night upon the surface of the sea," a spectacle,” says Humboldt, “which stamped upon my memory an ineffaceable impression, and always excited fresh astonishment, although it was renewed every night for months together. It

may be seen in every zone; but those who have not witnessed it within the tropics, and above all upon the main ocean, can form but a very imperfect conception of the grandeur of the phenomenon, particularly if the spectator places himself in the shrouds of a ship of the line, during a fresh breeze, when she ploughs through the crests of the waves, and at every roll her side is raised out of the water enveloped in ruddy flames, which stream like lightning from the keel, and flash towards the surface of the sea.

At other times, the dolphins, while sporting in the waters, trace out sparkling furrows in the midst of the waters.” Some naturalists are of opinion that the phenomenon in question arises from electricity excited by the friction of the water upon the sides of the advancing ship,-an opinion upon which the author places no reliance. It is indisputable that there are several luminous molluscæ which have the faculty of emitting a phosphorescent light at pleasure, and also innumerable microscopic animalcules, possessing the same power, which have been found in the waters thus illuminated, and to whose presence the phenomenon has been ascribed. Let us however hear Mr. Rennie on the subject.

• But though these may be partly or sometimes the cause, yet, in the greater number of instances, no animalcules whatever can be discovered in the luminous water, even by the aid of the best glasses. Such was the decision come to by Humboldt from numerous observations in the tropical seas, and his authority is one of the highest which can be adduced. We had recently an opportunity of repeating these observations at Hâvre de Grace, and could not discover the slightest

trace of animalcules, although the water which we examined was so strongly luminous, that it shone upon

the skin of some night-bathers like scattered clouds of lambent flame, appearing more as a property of the water itself than any thing extraneous diffused through it; but we particularly remarked that no light appeared in

[ocr errors]
[ocr errors]

quiescent water, it being only seen when the surface was broken by the ripple of the tide, or when a wave dashed upon the pebbles on the beach.

Humboldt, however, is of opinion, that though the phenomenon is only at times caused by animated lamp-bearers, it may probably arise in general from the decomposed fibrillæ of dead molluscæ which abound beyond all calculation in the bosom of the waters. He proved this by passing some of the luminous water through cloth, when some of the fibrillæ were separated, and appeared in the form of luminous points. We should, on the other hand, have been inclined to infer that these points were caused by the luminous water moistening the fibres of the cloth: and our author himself afterwards seems to abandon the notion of fibrillæ for that of a gelatinous fluid produced by the decomposition of the dead bodies, and imparting to sea-water the nauseous taste, which is as much disliked by us as it is relished by the fishes. Water may thus be rendered luminous by throwing into it a quantity of herring brine, and hence it appears that salt is indispensable ; for, as M. Bory de St. Vincent justly remarks, the waters of our lakes and marshes are never luminous, though these abound with polypi, both living and dead. There seem also to be certain states of the air favourable or unfavourable to the development of the light; for one night it will appear with great brilliance, while on the following, though the circumstances seem all equal, it will be gone. It seems to be the more frequent, as Humboldt remarked, “ when the sky was thick and cloudy, and upon the approach of a storm.” We have remarked it as frequently following as preceding a storm; but it seems to be independent of heat or cold; for on the banks of Newfoundland it is observed to shine with great brilliance during the most vigorous frosts.'—pp. 232, 233.

One of the most wonderful facts connected with the history of insects, from which the phenomenon just mentioned has rather led us away, is that of the aphides, which are always so abundant wherever ants are found, (forming indeed their principal food) being produced without pairing. This fact has been placed beyond doubt by several experiments. The aphis is born, changes its skin three or four times, like the caterpillar, and after its last moult is completed, gives birth, without any further process, to hundreds of young aphides, which go through the same operations in their turn. This mode of propagation has been proved to have taken place as far as the ninth generation. When the female is at length exhausted, she can produce no more without pairing; it is however very remarkable, that when this occurs, she produces not the living insects as before, but eggs, or pupæ like eggs, whereas the insects to which these eggs or pupæ give birth, take up the original character of the species, and without pairing produce many living generations. More wonderful still must we deem the fact to be, that all these broods are uniformly females, no males being produced till the pairing season, which is towards the close of summer or autumn.

The migration of insects forms another very curious subject, well worth the attention of the naturalist. With respect to their modes

of government, many fanciful theories have been broached from time to time, and it does not appear that a sufficient number of facts has as yet been collected, to establish any thing like a consistent history of their internal policy. It is well known that among the ants there is a most complete division of labour; they have their workers who are incessantly employed in erecting, enlarging, or repairing their buildings, foraging for provisions, and attending to the

eggs and the young ; soldiers in the proportion of about one to every hundred of the workers, well armed, and always on the watch to defend the colony from invasion; and males and females, whose sole business it is to propagate the species. The mode in which bees conduct their affairs, is familiar to every body. Insects have also, like their lordly masters, their wars; sometimes carried on after the manner of duels, sometimes upon a more extensive scale, when whole armies march against each other.

• Besides attacking the larger animals, however, individuals of adjacent hives often engage in fatal duels. Sometimes a bee, while sitting peaceably on the outside of a hive or walking about, is rudely jostled by another, when the combat immediately commences with such bitter violence, that they permitted Réaumur to examine them quite closely with a magnifying glass. They wrestle, turn, pirouette, and throttle each other; and after rolling about in the dust, the victor, watching the time when the enemy uncovers his body by elongating it in the attempt to sting, thrusts its weapon between the scales, and the next instant its antagonist stretches out its quivering wings, and expires; for the stroke of the sting, when it once penetrates the muscle, is mortal. In these engagements the conqueror is not always able to extricate his sting, and then both perish. The duration of such duels is uncertain ; sometimes it lasts an hour, and at others is very soon determined ; and occasionally it happens that both parties, tired with their fruitless struggles, give up the contest and fly off.”pp. 328, 329.

When a hive happens to be ill-managed, or has had an unfortunate season from some cause or other, the inhabitants mutiny, and become a band of robbers. This happens generally in March or August. - When a hive determines on the predatory system,” says Keys, they send spies to discover the state of neighbouring stocks. A few of the spies for several days dodge about the doors, trying to get in to obtain more knowledge of their strength and riches; but are driven away by the powerful, who plant guards at their door, and as the weak stocks do not, they are therefore the first to be assaulted. The next day they return in force, and begin a violent siege ; and a desperate conflict ensues, both within and without the hive, neither side giving quarter. The stoutest warriors make a desperate attempt, and rush forward and seize the queen ; knowing that by dispatching her, instant victory is the consequence; for the assaulted bees always desist and join the victors the moment they are apprised of their queen's death, become as one fraternity,

« AnteriorContinuar »