possess four thin and membranous wings incapable of being folded. These possess a network of delicate nervures, giving the name Neuroptera (meaning nerve-winged) to the class. Of the forms mentioned above, all but the white ants lay their eggs in the water, and the developing larvæ

spend their lives in this medium until the time comes for their complete metamorphosis into the adult. The larvæ of the caddis-flies protect themselves within a tube of stones or sticks bound together with silken threads, which they usually attach to the under side of stones in running water. On the other hand, the young of the dragon- and may-flies, provided with strong jaws, are active in the search of food and very voracious. In time they emerge from their larval skin and the water in which they live, and after a life spent on the wing they deposit their eggs and perish. The adult ant-lion, a type of the related order (Neuroptera), which has somewhat the appearance of a small dragon-fly, lays its eggs in light sandy soil. In this the resulting larvæ excavate funnel-shaped pits, at the bottom of which they lie con

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cealed. Insects stumbling into their pitfalls are pelted with sand, which the ant-lion throws at them with a jerky motion of the head, and are speedily tumbled down the shifting sides of the funnel to be seized and devoured.

While the white ants are not in any way related to the true ants, they possess many similar habits. Associated in great companies, they excavate winding galleries in old logs. and stumps, and, further, are most interesting because of the division of labor among the various members. The wingless forms are divided into the workers, which excavate, care for the young, and otherwise labor for the good of the others; and into the soldiers, huge-headed forms,

FIG. 72.-Ant-lion larva plowing its way through the sand (upper figure) while another is commencing the excavation of a funnel-shaped pit similar to one on right. Photograph by A. L. MELANDER and C. T. BRUES.

whose strong jaws serve to protect the colony. The remaining winged forms are the kings and queens. In the spring many of the royalty fly away from home, shed their wings, unite in pairs, and set about to organize a colony. The queen rapidly commences to develop eggs, and in some

species her body becomes so enormously distended with these that she loses the power of locomotion and requires to be fed. A single queen has been known to lay eggs at the rate of sixty per minute (eighty thousand a day), and

those destined to royal rank are so nursed that they advance farther in their development than the remaining sterile and wingless forms.

118. The bugs (Hemiptera).-The large and varied group of the bugs (Hemiptera) includes a number of semi-aquatic species, such as the water-boatmen, often seen rowing themselves along in the ponds by means of a pair of oarshaped legs, in search of other insects. Somewhat similar at first sight are the back-swimmers, with like rowing habits, but unique in swimming back downward. Both of these bugs frequently float at the surface, and when about to undertake a subaquatic journey they may be seen to imprison a bubble of air to take along. Closely related are the giant water-bugs (Fig. 74), which often fly from pond to pond at night. In such flights they are frequently

attracted by lights, and have come to be called "electriclight bugs."

Among our most dreaded insect pests are the chinchbugs-small black-and-white insects, but traveling in companies aggregating many millions.

As they go they feed upon the stems and leaves of grain, which they devour with extraordinary rapidity. The squash-bug family is also extensive, and destructive to the young squash and pumpkin plants in the early spring.

The lice are small, curiously shaped bugs, which suck the blood of other animals. The plant-lice, also small, suck the juices of plants, and are often exceedingly destructive. This is especially true of the phylloxera, a plant-louse

FIG. 74.-Giant water-bug (Ser- which causes annually the loss of

millions of dollars among the vineyards of this and other countries. Even more destructive are the scale-insects, curiously modified forms, of which the wingless females may be found on almost any fruit-tree and on the plants in conservatories, their bodies covered with a downy, waxy, or other kind of covering, beneath which they remain and lay their eggs.

119. The flies (Diptera).-The group of the Diptera (meaning two-winged) includes the gnats, mosquitoes, fleas, house-flies, horse-flies (Fig. 75), and a vast company of related forms. Only a single pair of wings is present, the second pair being rudimentary or fashioned into short, thread-like appendages known as balancers, though they probably act as sensory organs and are not directly concerned with flight. The mouth-parts are adapted for piercing and sucking. The eyes, constructed on the same plan

as those of the Crustacea, are comparatively large, and are frequently composed of a great number of simple eyes united together, upward of four thousand forming the eye of the common house-fly.

These insects are widely distributed throughout the world, where they inhabit woods, fields, or houses as best suits their needs. Their food is varied. Some suck the juices of plants, others attack animals, and, while many are troublesome pests, others, especially in the early stages of their existence, are of great benefit.

A

FIG. 75.-Horse-fly (Therioplectes).

120. Familiar examples.-Owing to the widely different habits and structure of the members of this group, we shall briefly consider two examples, the mosquito and the house-fly, which will give us a fairly good idea of the characteristics of all. The eggs of the mosquito are laid in sooty-looking masses on the surface of stagnant pools. Within a very short time the young hatch, and, owing to their pecul iar swimming movements, are known as "wrigglers." They are then active scavengers, devouring vast quantities of noxious substances and performing a valued service. They frequently rise to the surface, take air into the tracheal system, which opens at the posterior end of the body, and descend again. After an increase in growth and many internal changes resulting in a chrysalis-like stage, they rise to the surface, split the shell, and, using the latter as a float, carefully balance themselves and soon fly away.

The house-fly usually lays its eggs in decaying vegetable matter, and the young, maggot-like in form, are active scavengers. They too undergo deep-seated changes during the next few days, finally transforming into the adult.