Facts and Thoughts about Spiders. 185 



grain can instantaneously shoot out filaments twenty 

 or thirty inches long, and by means of which it 

 floats itself in the air. 



Naturalists are now giving a great deal of atten- 

 tion to the migrations of birds in diiferent parts of 

 the world : might not insect and spider migrations 

 be included with advantage to science in their ob- 

 servations ? The common notion is that the 

 gossamer makes use of its unique method of locomo- 

 tion only to shift its quarters, impelled by want of 

 food or unfavourable conditions — perhaps only by 

 a roving disposition. I believe that besides these 

 incessant Sittings about from place to place 

 throughout the summer the gossamer-spiders have 

 great periodical migrations which are, as a rule, in- 

 visible, since a single floating web cannot be re- 

 marked, and each individual rises and floats away 

 by itself from its own locality when influenced by 

 the instinct. When great numbers of spiders rise 

 up simultaneously over a large area, then, some- 

 times, the movement forces itself on our attention ; 

 for at such times the whole sky may be filled with 

 visible masses of floating web. All the great move- 

 ments of gossamers I have observed have occurred 

 in the autumn, or, at any rate, several weeks after 

 the summer solstice ; and, like the migrations of 

 birds at the same season of the year, have been in 

 a northerly direction. I do not assert or believe 

 that the migratory instinct in the gossamer is uni- 

 versal. In a moist island, like England, for 

 instance, where the condition of the atmosphere is 

 seldom favourable, and where the little voyagers 

 would often be blown by adverse winds to perish 



