INSTINCT. 



17 



I mean Aphides and Locusts, are the best 

 examples of this order. 



" So much as the world has suffered from 

 these animals, it is extraordinary that so few 

 observations have been made upon their history, 

 economy, and mode of proceeding. 



" The eggs of the locusts were no sooner 

 hatched in June," says Dr. Shaw, " than each 

 of the broods collected itself into a compact 

 body, of a furlong or more in square, and then 

 marching directly forwards towards the sea, they 

 let nothing escape them ; they kept their ranks 

 like men iifwar, climbing over as they advanced 

 every tree or wall that was in their way ; nay, 

 they entered into our very houses and bed- 

 chambers like so many thieves. A day or two 

 after one of these hordes was in motion, others 

 were already hatched to march and glean after 

 them. Having lived near a month in this 

 manner they arrived at their full growth, and 

 threw off their ni/mpha state by casting their 

 outward skin." " The transformation was per- 

 formed in seven or eight minutes, after which 

 they lay for a short time in a torpid and seem- 

 ingly languishing condition; but as soon as the 

 sun and the air had hardened their wings by dry- 

 ing up the moisture that remained on them after 

 casting their sloughs, they re-assumed their 

 former voracity with an addition of strength 

 and agility." 



" According to Jackson they have a govern- 

 ment amongst themselves similar to that of the 

 bees and ants; and when the king of the locusts 

 rises, the whole body follow him, not one soli- 

 tary straggler being left behind. But that 

 locusts have leaders like the bees or ants, dis- 

 tinguished from the rest by the size and splen- 

 dour of their wings, is a circumstance that has 

 not yet been established by any satisfactory 

 evidence; indeed, very strong reasons maybe 

 urged against it." 



" The last order of imperfect associations 

 approaches nearer to perfect societies, and is 

 that of those insects which the social principle 

 urges to unite in some common work for the 

 benefit of the community. 



" Many larvae of Lepidoptera associate 

 with this view, some of which are social only 

 during part of their existence, and others during 

 the whole of it. 



" A still more singular and pleasing spectacle 

 when their regiments march out to forage, is 

 exhibited by the Processionary Bombyx. This 

 moth, which is a native of France and has not 

 yet been found in this country, inhabits the 

 oak. Each family consists of from 600 to 800 

 individuals. When young, they have no fixed 

 habitation, but encamp sometimes in one place 

 and sometimes in another under the shelter of 

 their web ; but when they have attained two- 

 thirds of their growth, they weave for themselves 

 a common tent. About sun-set the regiment 

 leaves its quarters; or, to make the metaphor 

 harmonize with the trivial name of the animal, 

 the monks their coenobium. At their head is a 

 chief, by whose movements their procession is 

 regulated. When he stops all stop, and pro- 

 ceed when he proceeds ; three or four of his 

 immediate followers succeed in the same line, 



VOL. III. 



the head of the second touching the tail of the 

 first ; then comes an equal series of pairs, next 

 of threes, and so on as far as fifteen or twenty. 

 The whole procession moves regularly on with 

 an even pace, each file treading on the steps of 

 those that precede it. If the leader, arriving 

 at a particular point, pursues a different direc- 

 tion, all march to that point before they turn."* 

 Examples of occasional associations, more 

 or less resembling all these, and of which the 

 object is in many instances still obscure, may 

 be found in all the classes of the higher ani- 

 mals, as is obvious, when we consider to how 

 many tribes of animals the term gregarious is 

 usually applied, e. g. to almost all the Rumi- 

 nantia, some of the Pachydermata, and a few of 

 the Rodentia. Some of the genus Muridse (rats 

 and mice) have been long known to migrate, 

 occasionally, in a manner resembling the 

 locusts. " The general residence of the lem- 

 ming," says Pallas, " is in the mountainous 

 parts of Lapland and Norway, from which 

 tracts at uncertain periods it descends in im- 

 mense troops, and by its incredible numbers 

 becomes a temporary scourge to the country, 

 devouring the grain and herbage, and com- 

 muting devastations equal to those of an army 

 of locusts." " It is observable that their chief 

 emigrations are made in the autumns of such 

 years as are followed by severe winters." " The 

 ground over which they have passed appears 

 at a distance as if it had been ploughed, the 

 grass being devoured to the roots in numerous 

 stripes or parallel paths, of one or two spans 

 broad, and at the distance of some yards from 

 each other." " The army moves chiefly at night, 

 or early in the morning. No obstacles that 

 they meet in their way have any effect in 

 altering their route, neither fires, nor deep 

 ravines, nor torrents, nor marshes, nor lakes ; 

 they proceed obstinately in a straight line, and 

 hence many thousands perish in the waters." 

 " If disturbed, in swimming over a lake, by oars 

 or poles, they will not recede, but keep swim- 

 ming directly on, and soon get into regular 

 order again." " In their passage over land, if 

 attacked by men, they will raise themselves up, 

 uttering a kind of barking sound, and fly at 

 the legs of their invaders, and will fasten so 

 fiercely on the end of a stick, as to suffer them- 

 selves to be swung about without quitting their 

 hold, and are with great difficulty put to flight." 

 " The major part of these hosts is destroyed by 

 various enemies, as owls, hawks, weasels, ex- 

 clusively of the number that perish in the 

 waters, so that but a small part survive to 

 return, as they are sometimes observed to do, 

 to their native mountains." The campagnol, 

 or short-tailed rat, has been known to com- 

 mit similar ravages in France. It is obvious 

 here, that under the influence of this instinct, 

 and of the excitement of numbers (in which, 

 as in our own race, the principle of imitation 

 is probably much concerned) the usual motives 

 to action of these animals are superseded, and 

 their usual habits changed. 



We are still uncertain as to the use, or final 



* Introduction to Entomology, letter xvi. 



c 



