The under-water battles in which these mud dragons, or dragon-fly nymphs, take part must be something terrible. It is recorded that in Hungary 50,000 young fishes were put into a pond in which enormous numbers of these nymphs occurred and only fifty-four fishes survived. One is not surprised to learn, too, that they will eat each other up. On the whole, however, it is doubtful if between the flies and other injurious insects which the dragon-flies destroy in the air, and those larvæ of mosquitos which the water nymphs destroy in the ponds, there is any other family of insects toward which man should feel more indebted than toward the family of the odontata or dragon-flies. [Illustration] AN ABANDONED DRAGON CASE (_Libellulid_) From this muddy outworn shell, left to decay at the bottom of a pool, there came, sometime last summer, a gorgeous, four-winged dragon-fly. A little after dawn, what was once this water nymph or mud dragon, tired perhaps of its mud existence, ready anyway for the transformation, crawled up out of the water upon some stone or stick and waited there for its back to split open up and down. It pulled its soft, boneless legs from their cases, now lying along the abandoned shell, its wings closely packed together from the two cases on its back and its head and jaws from out the broken head shell. Even every air passage running through its body shed its parchment lining. Soft and helpless it crawled away into the grass to wait until its wet, soft outer skeleton should harden and make it possible for the powerful wing muscles to pull against it and for the broad wing films to dry and straighten out. By noon the transformation was doubtless quite complete, and flitting across the pond went the recent inhabitant of this dragon-fly case. [Illustration] THE DAMSEL FLY (_Agrion maculatum_, Beauvois) Most insects' legs are made to walk with, but those of the dragon-fly are not. They are bunched together so near the head that when the creature alights it can do little more than cling to what it lights upon. Instead, the legs, with their spines, form a perfect basket, open towards the front, and thus become the organs with which flies are caught. This damsel fly, as it is called, is smaller and more delicate than the dragon-fly with quite a different head. It inhabits shrubby woodland and is not often seen. Some of its tropical relatives are creatures of extraordinary fragility and delicacy. Its wings, which move in perfect unison, although distinct, are operated by such ingenious mechanical devices within the body as to have long ago suggested a flying machine, and it is strange how like a dragon-fly Professor Langley's aerodrome, the first of them all, does look, although of course the aerodrome's wings were rigid. One realizes what enormous eyes these dragon-flies have when one begins to compare them with the size of the head. [Illustration] THE LACE-WINGED FLY AND THE APHIS LION (_Chrysopa sp._)