The regular arrangement of these plates, one beside and partly covering the other, as in the tiling of an house, is best seen by examining a wing in the opake microscope. The prodigious number of small scales which cover the wings of these beautiful insects, is a sure proof of their utility to them, because they are given by HIM who makes nothing in vain.
That the lively and variegated colours, which adorn the wings of the moth and butterfly, arise from the small scales or plates that are planted therein, is very evident from this, that if they be brushed off from it, the wing is perfectly transparent: but whence this profusion and difference of colour on the same wing? is a question as difficult to resolve, as that of Prior, when he asks.
| “Why does one climate and one soil endue | - | |
| The blushing poppy with a crimson hue, | ||
| Yet leave the lilly pale, and tinge the violet blue?” |
As the wings of the moths and butterflies are very light, they can support themselves for a long time in the air; their manner of flying is ungraceful, generally moving in a zigzag line, to the right and to the left, alternately ascending and descending; this undulating motion however has its uses, as it disappoints the birds who chase them in taking aim; by which means they frequently elude their pursuit, though continued for a considerable time.
Dr. Hooke[58] endeavoured to investigate the nature of the motions of the wings of insects; and, although he was not able, from the experiments he made, to give a satisfactory account of them, yet as they may be useful to some future inquirer, and lead him more readily into the path of truth, I hope an extract therefrom will not prove unacceptable to the reader. To investigate the mode or manner of moving their wings, he considered with attention those spinning insects that suspend, or as it were poise themselves in one place in the air, without rising or falling, or even moving backwards or forwards; by looking down on these, he could, by a kind of faint shadow, perceive the utmost extremes of the vibratory motion of their wings; the shadow, while they were thus suspended, was not very long, but was lengthened when they endeavoured to fly forwards. He next tried by fixing the legs of a fly upon the top of the stalk of a feather with glue, wax, &c. and then making it endeavour to fly away; he was thereby able to view it in any posture. From hence he collected, that the extreme limits of the vibrations were usually somewhat about the length of the body distant from each other, often shorter, and sometimes longer. The foremost limit was generally a little above the back, and the hinder one somewhat beneath the belly; between these, to judge by the sound, they seemed to move with an equal velocity. The manner of their moving them, if a just idea can be formed by the shadow of the wing, and a consideration of its nature and structure, seemed to be this: the wing being supposed to be in the extreme limit, it is then nearly horizontal, the forepart only being a little depressed; in this situation the wing moves to the lower limit; before it arrives at this, the hinder part begins to move fastest; the area of the wing begins to dip behind, and in that posture it seems to be moved to the upper limit back again. These vibrations, judging by the sound, and comparing them with a string tuned in unison thereto, consist of many hundreds, if not thousands, in a second of time. The powers of the governing faculty of the insect, and the vivacity of its sensations, whereby every organ is stimulated to act with so much velocity and regularity, surpass our present comprehension.
[58] Hooke’s Micrographia, p. 172.
PEDES THE FEET, AND LEGS OF INSECTS.
These are admirably adapted for their intended service, to give the most convenient and proper motion, and, from the variety in their construction, their various articulations, &c. furnish the microscopic observer with an abundance of curious and interesting objects: the most general number is six; many of the class aptera have eight, as the spider; the crab has ten; the oniscus fourteen; the julus has from seventy to one-hundred and twenty on each side. The legs of those insects that have not more than ten, are affixed to the trunk; while those that exceed that number, have part fixed to the trunk, the rest to the abdomen.
The legs of insects are generally divided into four parts. The first, which is usually the largest, is called the femur; the second, or tibia, is joined to the former, and is commonly of the same size throughout, and longer than the femur; this is followed by the third part, which is distinguished by the name of tarsus, or foot; it is composed of several joints, the one articulated to the other, the number of rings varying in different insects; the tarsus is terminated by the unguis, or claw.
The writers on natural history, in order to render their descriptions clear and accurate, have given several names to the legs of insects, from the nature of the motions produced by them. Thus cursorii, from that of running; these are the most numerous. The saltatorii, those that are used for leaping; the thighs of these are remarkably large, by which means they possess considerable strength and power to leap to great distances. The natatorii, those that serve as oars for swimming; the feet of these are flat and edged with hairs, possessing a proper surface to strike against the water, as in the dytiscus, notonecta, &c. Such feet as have no claws are termed mutici. The chelæ, or claws, are an enlargement of the extremity of the fore feet, each of which is furnished with two lesser claws, which act like a thumb and finger, as in the crab. The under part of the feet in some insects is covered with a kind of brush or sponge, by which they are enabled to walk with ease, on the most polished substances, and in situations from which it would seem they must necessarily fall.