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 flittimgs 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, tiie 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 
