appearance represented in Fig. 96. At the proper time they crawl out of the ground, and their skins splitting open along the back, out come the perfect insects, with wings and all complete, to fly away, lay their eggs, and devastate the

forests.

There are certain species which do not occur in such numbers, and which pass through all their changes in a single year. The cast-off skins of the pupa of such species may be often found clinging to apple-trees and fences in New England.

FIG 96.-PUPA-CASE OF A SPECIES OF NEW ENGLAND CICADA OR HARVEST-FLY, CLINGING TO A TWIG.

The pupils should, if possible, collect a twig in which the eggs have been deposited, a pupa-skin, and the perfect insect.

CHAPTER XIV.

HABITS AND STRUCTURE OF INSECTS (CONCLUDED).

94. THE May-fly, or Ephemera, is one of the most common insects in the Western States. They live only a few weeks in their perfect state, oftentimes but a few days. Their eggs are laid in the water, and the larvæ live in the water two or three years. At the end of this time they come to the surface in immense numbers, and, shedding their skins, come out as winged insects. At this time they resemble their perfect state so closely, that the name sub

FIG. 97.-LARVA OF EPHEMERA.

(Reduced from Figure by J. H. Emerton, in Dr. A. S. Packard's Directions for collecting Insects, Smithsonian Institution.)

imagos is given to them in this condition. They often fly a considerable distance from the water, alighting on the ground and trees. Here they again shed their skin, and then have attained their perfect state.

These insects occur in prodigious numbers in certain parts of the world. In some regions of Europe they are so

FIG. 98.-EPHEMERA.

abundant that the inhabitants collect them in heaps, and use them as dressing for the land. In the cities bordering the

great lakes it is a common sight to see the gas-posts and adjoining buildings blackened by the myriads of Ephemera which have been blown in from the lakes and have been attracted by the lights. The following figure represents a gas-post, in Cleveland, Ohio, as it appeared with Ephemera clinging to it:

LAKE ST

FIG. 99.-GAS-POST, WITH EPHEMERA CLINGING TO IT.

95. Another group of insects somewhat resembling the Ephemera pass their larval state in the water.

Some of their larvæ are called caddis-worms, or case

worms, and are inclosed in cases of cylindrical and other shapes. These are variously made of grains of sand, bits of bark and sticks, and other fragments of convenient size cemented together. Some of these cases, built of small

FIG. 100.-CADDIS-WORM, WITH ITS CASE.

grains of sand, look like coiled snail-shells. Other larvæ shelter themselves in bits of straw, or the fragments of hollow stems of plants.

Fig. 100 represents the larva of one of these insects in its case, which is made of bits of sticks arranged in a spiral The larva drags about this case, and as it grows col

course.

lects material for the enlargement of its tube.

In almost any quiet pool or running stream these curious cases may be found, containing the larvae within.

FIG. 101.-GALL-FLY.

96. The curious round balls called gall-nuts, which are found on the leaves of the oak and of other trees, are produced by an insect called the gall-fly.

The eggs are deposited in the substance of the leaf, and