It also possessed a protective habit common to most
grasshoppers, of embracing a slender vertical stem with its four fine
front legs, and moving cunningly round so as to keep the stem always in
front of it to screen itself from sight. Only other grasshoppers are
silent when alarmed, and the silence and masking action are related, and
together prevent the insect from being detected. But this particular
species, or race, or colony, living on the sides of the isolated sierra,
had acquired a contrary habit, resembling a habit of gregarious birds
and mammals. For this informing sound (unless it mimicked some
_warning-sound,_ as of a rattlesnake, which it didn't) could not
possibly be beneficial to individuals living alone, as grasshoppers
generally do, but, on the contrary, only detrimental; and such a habit
was therefore purely for the public good, and could only have arisen in
a species that always lived in communities.
On another occasion, in the middle of the hot season, I was travelling
alone across-country in a locality which was new to me, a few leagues
east of La Plata River, in its widest part. About eleven o'clock in the
morning I came to a low-lying level plain where the close-cropped grass
was vivid green, although elsewhere all over the country the vegetation
was scorched and dead, and dry as ashes. The ground being so favourable,
I crossed this low plain at a swinging gallop, and in about thirty
minutes' time.
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