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
Summer"--the flying or departing summer.
I have stated that all migrations of gossamers I have witnessed have
been in the autumn; excepting in one instance, these flights occurred
when the weather was still hot and dry. The exceptionally late migration
was on March 22--a full month after the departure of martins,
humming-birds, flycatchers, and most other true bird-migrants.
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