146 VORACITY OF INSECTS. 
Some feed only upon the outside of the leaves; some upon — 
the internal tissue ; others upon the flowers or on the fruit; _ 
a few will eat nothing but the bark ; while many derive their — 
nourishment only from the woody substance of the trunk. : 
146. The excessive multiplication of certain tribes of - 
Insects has sometimes had the effect of devastating an entire 
country. Thus the “plague of locusts” is not unfrequently: 
repeated in tropical countries, and is dreaded by the inhabi- 
tants even more than an earthquake. These insects are of 
such extreme voracity that no green thing escapes them ; 
and when their numbers are so increased that they fly in 
masses which look like dark clouds, and cover the ground 
where they alight for miles together, it may be easily con- 
ceived that the devastation they create must produce incal- 
culable injury. The north of Africa and the west of Asia are 
the countries most infested by these pests. It is related by 
Augustin, that a plague, induced partly by the famine they 
had created, and partly by the stench occasioned by their 
dead bodies, carried off 800,000 inhabitants from the kingdom 
of Numidia and the adjacent parts. They occasionally attack 
the south of Europe. It is recorded that Italy was devastated 
by them in the year 591; and that a prodigious number both 
of men and beasts perished from similar causes,—no less 
than 30,000 persons in the kingdom of Venice alone. These 
tremendous swarms usually advance towards the sea; and 
being there checked, and having completely exhausted the 
country behind them, they themselves die of famine, or are 
blown into the sea by a gale. In 1784 and 1797, they de- 
yastated Southern Africa; and it is stated by Mr. Barrow 
(in his Travels in that country) that they covered a surface 
of 2,000 square miles; that, when cast into the sea by a 
strong wind from the north-east, and washed upon the beach, 
they formed a line fifty miles long, and produced a barrier 
along the coast three or four feet high; and that, when the 
wind again changed, the stench created by the putrefaction 
of their bodies was perceived at a distance of 130 miles 
inland. A similar event occurred in the Barbary States in 
1799, and was followed, as in the other cases, by a plague. 
147. We have occasionally an example of similar devasta- 
tion in our own country, though on a smaller scale. Thus, 
a few years ago, the turnip-crops of some parts of England 
