466 MOTIONS OF INSECTS. 



Thomson's Annals of Philosophy l , under the signature of Carolan, has 

 given some curious observations on the mode in which some geometric 

 spiders shoot and direct their threads, and fly upon them; by which it 

 appears that as they dart them out they guide them as if by magic, emitting 

 at the same time a stream of air, as he supposes, or possibly some subtile 

 electric fluid. One, which was running upon his hand, dropped by its 

 thread about six inches from the point of his finger, when it immediately 

 emitted a pretty long line at a right angle with that by which it was sus- 

 pended. This thread, though at first horizontal, quickly rose upwards, 

 carrying the spider along with it. When it had ascended as far above his 

 finger as it had dropped before below it, it let out the thread by which it 

 had been attached to it, and continued flying smoothly upwards till it 

 nearly reached the roof of the room, when it veered on one side and 

 alighted on the wall. In flying, its motion was smoother and quicker than 

 when a spider runs along its thread. He observes, that as the line lengthens 

 behind them, the tendency of spiders to rise increases. I have myself 

 more than once observed these creatures take their flight, and find the 

 following memorandum with respect to their mode of proceeding : " The 

 spider first extends its thighs, shanks, and feet into a right line, and then 

 elevating its abdomen till it becomes vertical, shoots its thread into the 

 air, and flies off from its station." It is not often, however, that an ob- 

 server can be gratified with this interesting sight, since these animals are 

 soon alarmed. I have frequently noticed them for at the times when 

 these webs are floating in the air they are very numerous on the vertical 

 angle of a post or pale, or one of the uprights of a gate, with the end of their 

 abdomen pointing upwards, as if to shoot their thread previously to flying 

 oft ; when, upon my approaching to take a nearer view, they have lowered 

 it again, and persisted in disappointing my wish to see them mount aloft. 

 The rapidity with which the spider vanishes from the sight upon this oc- 

 casion, and darts into the air, is a problem of no easy solution. Can the 

 length of web that they dart forth counterpoise the weight of their bodies ; 

 or have they any organ analogous to the natatory vesicles of fishes 2 , which 

 contributes at their will to render them buoyant in the air ? Or do they 

 rapidly ascend their threads in their usual way, and gather them up, till 

 having collected them into a mass of sufficient magnitude, they give them- 

 selves to the air, and are carried here and there in these chariots ? I must 

 here give you Mr. White's very curious account of a shower of these webs 

 that he witnessed. On the 21st of September, 1741, intent upon field 

 diversions, he rose before daybreak ; but on going out he found the whole 

 face of the country covered with a thick coat of cobweb, drenched with 

 dew, as if two or three setting-nets had been drawn one over the other. 

 When his dogs attempted to hunt, their eyes were so blinded and hood- 

 winked that they were obliged to lie down and scrape themselves. This 

 appearance was followed by a most lovely day. About nine A. M. a shower 

 of these webs (formed not of single floating threads, but of perfect flakes, 

 some near an inch broad, and five or six long) was observed falling from 

 very elevated regions, which continued without interruption during the 

 whole of the day ; and they fell with a velocity which showed that they 

 were considerably heavier than the atmosphere. When the most elevated 

 station in the country where this was observed was ascended, the webs 



l No. lii. 306. 2 Cuvier, Anat. Comp. i. 504. 



