442 MOTIONS OF INSECTS. 



path that it may find it again ; but thus, whenever the caterpillar falls or 

 would descend from a leafj 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 

 larvae 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 sphincter, 

 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, how- 

 ever, it soon disengages itself, between the two last pairs of perfect legs. 1 

 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. Some- 

 times, 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 larvae 

 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 in- 

 habit that element. Amongst the beetles, the genera Dytiscus, Hydro- 

 philus, Gyrinus, Limnius, Parnus, Heterocerus, JElopkorus, Hydrcena, &c. ; 

 amongst the bug tribes, Gerris, Velia, Hydrometra, Notonecta, Sigara, Nepa, 

 Ranatra, Naucoris ; a few Lepidoptera ; the majority of Trichoptera ; Li- 

 bellula, Aeshna, Agrion, Sialis, Ephemera, &c. amongst the Neuroptera ; 

 Culex and many of the Tipular'we Latr. from the dipterous insects ; and 

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

 these, in their larva state, are aquatic animals. 



The motions of these creatures in this state are various. Some walk 

 on the ground under water; some move in mid-water, either by the same 

 motion of the legs as they use in walking, or by strokes, as in swimming ; 

 others for this purpose employ certain laminae, which terminate their 

 tails as oars ; others again swim like fish, with an equable motion ; some 

 move by the force of the water which they spirt from their anus ; others 



i Reaum. ii. 375. 



