certain periods of the year, in such prodigious numbers, that no one, who has not been a witness of the fact, would be capable of forming any idea of it. We must not suppose that these vast quantities of insects are permitted to exist without some important and useful purposes having to be performed by them. In the forests referred to, vegetation is not only exceedingly rapid, but the decay of it is equally so. Large trees, also, are thrown down by hurricanes or other causes, to which parasitical plants have clung. Forests, therefore, would become almost impassable, both for man or beast, and the atmosphere would be rendered most hurtful to them, if the decaying vegetable matter was not quickly consumed by myriads of insects. Notwithstanding all the researches of naturalists, and they have been great and indefatigable, the varieties of Beetles alone are so exceedingly numerous, that Mr. Darwin, in his "Researches in Natural History," says that it is sufficient to disturb the composure of an entomologist's mind to look forward to the future dimensions of a complete catalogue of these insects. It is also an interesting fact, that carnivorous beetles, and insects that feed on flesh, are very rare in these forests, while they abound in places where animals are very numerous. Mr. Darwin, in his agreeable and valuable work above referred to, states, that a person on first entering a tropical

forest, is astonished at the labours of the ants alone. Well-beaten paths may be seen, branching off in every direction, on which an army of neverfailing foragers are seen, some going forth, and others returning, burthened with pieces of green leaf, often larger than their own bodies.

The beautiful manner in which an Almighty Power has adapted certain insects to perform particular services, may be further illustrated by the following fact:-We know that the Caterpillars of many of our English butterflies feed on cabbages and lettuces. These vegetables are now cultivated in the gardens round Rio de Janeiro, having been of late years introduced there. Mr. Darwin informs us that neither the caterpillars of the numerous butterflies, which abound in that country to an extraordinary degree, or even the slugs, will touch them. Other food has been allotted to them to feed upon; in doing which they fulfil one of the designs for which they were created.

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We should also bear in mind, that in order to produce the necessary number of insects requisite carry on the purposes for which they were created, each species has its own particular habitation, in which the young can be lodged and protected. Many of these are formed with great skill, and shew astonishing ingenuity. The Mason-Bee, for instance, may be called an architect, for she makes a building composed of sand and mortar.

Some insects have the power of boring into decaying trees, which they do to a great length with considerable skill and perseverance.* Others penetrate into the earth, or drop their eggs in the water, while many live in communities, defending themselves and their young with so much courage, that even the largest animals have been obliged to yield to their united assaults.

It is evident, that the great multiplicity of insects would be attended with injury, if various causes did not serve to diminish their numbers, when there was an undue proportion of them. Birds devour them, and so do the larger tribe of insects, such as spiders, wasps, &c. Another cause of preventing a superabundant proportion of them, and of keeping down the numbers of certain insects, is the migratory principle which pervades certain species, during the progress of which vast numbers are destroyed. For instance, when the Beagle was off the shores of Northern Patagonia, and about ten miles from the Bay of San Blas, Mr. Darwin tells us, that vast numbers of butterflies, in bands or flocks of countless myriads, extended as far as the eye could range.

* Much has been said and written on the subject of the injury done to the elm trees in Hyde Park by a particular grub. I am, however convinced, that if the injured trees had been properly examined, either positive or incipient decay would have been found to have existed in them before the grubs attacked them.

Even with the aid of a glass, it was not possible to see a space free from butterflies. The seamen cried out," it was snowing butterflies," and such in fact, was the appearance.* The day had been fine and calm, and the one previous to it equally so. It is not, therefore, probable, that the insects were blown off the land, but we may conclude that they voluntarily took flight. Before sun-set, however, a strong breeze sprung up from the north, and this must have been the cause of tens of thousands of the butterflies having perished. This migratory instinct in insects is not confined to butterflies. Numerous beetles have been found far out at sea. Numbers of them were discovered seventeen miles from land, swimming in the open ocean, and apparently not much injured by the salt water.

The interesting fact of insects being blown from the Patagonian shore was observed by Captain Cook, and has been ably remarked upon by Mr. Darwin. Amongst other facts, he informs us that while the Beagle was in the mouth of the Plata, the rigging was coated with the web of the gossamer Spider. The weather had been fine and clear, and in the morning the air was full of patches of

* Captain Fitzroy, in his narrative, says, that this flight of white butterflies occupied a space of not less than two hundred yards in height, a mile in width, and several miles in length, and that they were as numerous as flakes of snow in the thickest shower.

the flocculent web, as on an autumnal day in England. The ship was then sixty miles distant from the land. Vast numbers of a small spider, about one-tenth of an inch in length, and of a dusky red colour, were attached to the webs. Many thousands of them were on the ship. The little aeronaut, as soon as it arrived on board, was very active, running about, sometimes letting itself fall, and then reascending the same thread; sometimes employing itself in making a small and very irregular mesh in the corners between the ropes. It moved with facility on the surface of the water. Its stock of thread appeared to be inexhaustible; and this I have observed to be the case with our own little gossamer, and, like them, when they were suspended by a single thread, the slightest breath of air would bear them out of sight. On other occasions, when they had been placed, or had crawled on some little eminence, they would send forth a thread, and sail away in a lateral course, with a rapidity which was quite unaccountable. Some spiders, however, have the power of darting through the air without the help of any thread. This I have noticed more than once, and it has been observed by others. M. Virey, in his "Bulletin des sciences naturelles," thinks, that by means of a rapid vibration of their feet, they walk the air. In the case of a spider, placed upon a stick, fixed in the centre of a basin-full of water, a thread is