precisely with the
aphides: some are particular, others more general feeders; and as they
resemble other insects in this respect, so they do also in being more
abundant in some years than in others.[959] In 1793 they were the chief,
and in 1798 the sole, cause of the failure of the hops. In 1794, a
season, almost unparalleled for drought, the hop was perfectly free from
them; while peas and beans, especially the former, suffered very much
from their depredations.

The ravages of the caterpillars of some of our smaller moths afford a
good illustration of the temporary increase of a species. The oak-trees
of a considerable wood have been stripped of their leaves as bare as in
winter by the caterpillars of a small green moth (_Tortrix viridana_),
which has been observed the year following not to abound.[960] The
silver Y moth (_Plusia gamma_), although one of our common species, is
not dreaded by us for its devastations; but legions of their
caterpillars have at times created alarm in France, as in 1735. Reaumur
observes that the female moth lays about four hundred eggs; so that if
twenty caterpillars were distributed in a garden, and all lived through
the winter and became moths in the succeeding May, the eggs laid by
these, if half of them were female and all fertile, would in the next
generation produce 800,000 caterpillars.[961] A modern writer,
therefore, justly observes that, did not Providence put causes in
operation to keep them in due bounds, the caterpillars of this moth
alone, leaving out of consideration the two thousand other British
species, might soon destroy more than half of our vegetation.[962]

In the latter part of the last century an ant most destructive to the
sugar-cane (_Formica saccharivora_), appeared in such infinite hosts in
the island of Granada, as to put a stop to the cultivation of that
vegetable. Their numbers were incredible. The plantations and roads were
filled with them; many domestic quadrupeds, together with rats, mice,
and reptiles, and even birds, perished in consequence of this plague. It
was not till 1780 that they were at length annihilated by torrents of
rain, which accompanied a dreadful hurricane.[963]

_Devastations caused by locusts._--We may conclude by mentioning some
instances of the devastations of locusts in various countries. Among
other parts of Africa, Cyrenaica has been at different periods infested
by myriads of these creatures, which have consumed nearly every