Facts and Thoughts about Spidei^s, 185 
grain can instantaneously slioot 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 flittings 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 
