90 ZOOLOGY. 
Insects are all animals of small size. The largest are tropical, amongst 
which are butterflies of almost a foot across the expanded wings. Insects 
abound far more in warm than in cold climates. The different species 
are very numerous, those of beetles alone exceeding in number all the 
kinds of vertebrated animals. 
A few species of Insects are important for their usefulness to man ; but. 
a far greater number are remarkable for the injuries they inflict by the 
destruction of herbage and crops or of articles of food or raiment. Of 
noxious insects, locusts may perhaps be regarded as the chief. Of insects 
useful to man, bees and silkworms deserve to be first named, and after 
them the cochineal insect and blistering-flies. | There are a few others to 
which we are indebted for substances useful in medicine and the arts. 
The instincts and habits of insects are very various and interesting. 
Many volumes have been written on those of bees and ants alone. 
Of the orders into which the class of Insects is divided by systematic 
naturalists, we must be contented with very briefly noticing only 
the most important. Taking first the insects which undergo complete 
metamorphoses, and in their perfect state have the mouth fitted for 
gnawing, tearing, and masticating, we find the order Coleoptera,’ dis- 
tinguished by having the first pair of wings modified into hard sheaths 
—called elytra, or wing-cases—to cover the second pair when not in 
use, and to protect the upper side of the abdomen, the wings being folded 
crosswise under these wing-cases. Coleopterous insects are sometimes 
collectively called beetles, although many of them are familiarly known 
by other names, as chafers, weevils, lady-bugs, &. The glowworm 
and fireflies belong to this order, as do also the valuable cantharides, or 
blistering-flies—The order Orthoptera? differs from Coleoptera chiefly in 
having the wing-covers of a soft substance, somewhat resembling parch- 
ment, and the wings folded longitudinally in a fan-like manner. To 
this order belong locusts, grasshoppers, and crickets; also those curious 
insects which, from their resemblance to leaves, twigs, and other 
objects, are known as leaf-insects or walking-leaves, walking-sticks, &e.— 
The order Newroptera® consists of insects having mouths similar to those 
of the orders already noticed, and four nearly equal and membranous 
wings, all adapted for flight, not folded in any way when at rest, 
and divided by their nervures—ribs or veins—into a delicate network. 
To this order belong dragon-flies, may-flies, ant-lions, and termites. or 
white ants. These last-named insects have social habits resembling those 
of the true ants. The great ant-hills of Africa and South America are 
constructed by them.—The order Hymenoptera * contains a vast number of 
1 From Greek coleos, a sheath, and pteron, a wing. 
2 From Greek orthos, straight, and pteron, a wing. 
3 From Greek mewros, a nerve or string, and pteron, a wing. 
4 From Greek hymen, a membrane, and pieron, a wing. 

