locomotion, 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 remarked, 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,
sometimes, 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 movements 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 universal. 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 far out at sea, it is difficult to believe that
such migrations take place. But where they inhabit a vast area of land,
as in South America, extending without interruption from the equator to
the cold Magellanic regions, and where there is a long autumn of dry,
hot weather, then such an instinct as migration might have been
developed. For this is not a faculty merely of a few birds: the impulse
to migrate at certain seasons affects birds, insects, and even mammals.
In a few birds only is it highly developed, but the elementary feeling,
out of which the wonderful habit of the swallow has grown, exists widely
throughout animated nature. On the continent of Europe it also seems
probable that a great autumnal movement of these spiders takes place;
although, I must confess, I have no grounds for this statement, except
that the floating gossamer is called in Germany "Der fliegender