MOTIONS OF INSECTS. 477 



far as they can reach with it ; then fastening their thread there, and 

 bringing up the rest of their body, they take another step ; never moving 

 without leaving this clue behind them ; the object of which, however, is 

 neither to measure, nor to mark its path that it may find it again ; but 

 thus, whenever the caterpillar falls or would descend from a leaf, it has 

 a cord always ready to support it in the air, by lengthening which it can 

 with ease reach the ground. Thus it can drop itself without danger 

 from the summit of the most lofty trees, and ascend again by the same 

 road. As the silky matter is fluid when it issues from the spinners, it 

 should seem as if the weight of the insect would be too great, and its 

 descent too rapid, so as to cause it to fall with violence upon the earth. 

 The little animal knows how to prevent such an accident, by descending 

 gradually. It drops itself a foot or half a foot, or even less, at a time; 

 then making a longer or shorter pause, as best suits it, it reaches the ground 

 at last without a shock. From hence it appears that these larvas 

 have power to contract the orifice of the spinners, so as that no more of 

 the silky gum shall issue from it ; and to relax it again when they intend 

 to resume their motion downwards : consequently there must be a mus- 

 cular apparatus to enable them to effect this, or at least a kind of sphinc- 

 ter, which, pressing the silk, can prevent its exit. From hence also it 

 appears that the gummy fluid which forms the thread must have gained a 

 degree of consistence even before it leaves the spinner, since as soon as 

 it emerges it can support the weight of the caterpillar. In ascending, 

 the animal seizes the thread with its jaws as high as it can reach it ; and 

 then elevating that part of the back that corresponds with the six perfect 

 legs, till these legs become higher than the head, with one of the last pair 

 it catches the thread ; from this the other receives it, and so a step is 

 gained : and thus it proceeds till it has ascended to the point it wishes to 

 reach. At this time if taken it will be found to have a packet of thread, 

 from which, however, it soon disengages itself, between the two last pairs 

 of perfect legs.^ To see hundreds of these little animals pendent at the 

 same time from the boughs of a tree, suspended at different heights, some 

 working their way downwards and some upwards, affords a very amusing 

 spectacle. Sometimes, when the wind is high, they are blown to the 

 distance of several yards from the tree, and yet maintain their threads 

 unbroken. I witnessed an instance of this last summer, when numbers 

 were driven far from the most extended branches, and looked as if they 

 were floating in the air. 



Having related to you what is peculiar in the motions of pedate larvse 

 upon the earth and in the air, I must next say something with respect to 

 their locomotive powers in the water. Numbers of this description inhabit 

 that element. Amongst the beetles, the genera Dyticus, Hydrophilus, 

 Gyrinus, Limnius, Parnus, Heterocerus, Elophorus, Hydraiia, he. amongst 

 the bug tribes, Gerris, Velia, Hydrometra, Notonccia, Sigara, Nepa, 

 Rnnatra, Naucoris ; a few Lepiduptera ; the majority of Trichoptera ; 

 Libcllula, Acshna, Agrion, Siolis, Ephemera, &c. amongst the Ncuroptera ; 

 Culex and many of the Tipularm Latr. from the dipterous insects ; and 

 from the Aptera, Atax, some Podurce, and many of the Oniscida, &c. 

 All these, in their larva state, are aquatic animals. 



» Reaum. ii. 375. 



