The boatmen, back-swimmers and giants all have oars, yet are not entirely dependent on them. They have strong wings, too, and if their old home gets too thickly settled, and the other insects on which they feed are scarce, they fly away to other places. The giant water-bug often migrates at night, and is attracted to any bright light he sees in his journey. This habit has given him the popular name of "electric-light bug." [Illustration: _Fig. 72. Water-scorpion._] [Illustration: _Fig. 73. Giant water-bug._] Among the insects which spend but part of their life in the water, we shall find many surprises. It made us feel queer when we learned that the restless but innocent-looking wiggler of the rain-water barrel was really the young of the too familiar mosquito. The adult mosquito leaves its eggs in tiny boat-shaped masses on the surface of stagnant water, where food will be abundant for the young which soon appear. Some time is spent by the wigglers in eating and growing before they curl up into pupæ. Insects are rarely active in the pupa stage. The mosquito is one of the very few exceptions. From these lively pupæ the full-grown mosquitoes emerge. Fig. 74 shows a small glass tumbler in which are seen the three aquatic stages of the mosquito's life and an adult just leaving the pupa skin. Nothing is easier than to watch the entire development of the mosquito, and the changes must be seen to be fully enjoyed and appreciated. It would be interesting to note the differences between the mosquitoes that come out of the small aquaria. A supply of wigglers may be kept in the permanent aquarium where they serve as food for the other insects. [Illustration: _Fig. 74. Temporary aquarium, containing eggs, larvæ and pupæ of mosquito._] Every child knows the dragon-fly or darning-needle, and none but the bravest of them dare venture near one without covering ears or eyes or mouth, for fear of being sewed. Many and wide-spread are the superstitions concerning this insect, and it is often difficult to bring children to believe that this creature, besides being a thing of beauty, is not only harmless but actually beneficial. If they knew how many mosquitos the darning-needle eats in a day they would welcome instead of fearing the gay creature. The young of the dragon-fly live a groveling existence, as different as can be from that of their sun-loving parents. Their food consists of mosquito larvæ, water-fleas and the like, and their method of catching their prey is as novel as it is effective. Pupils and teacher can get plenty of good healthy entertainment out of the behavior of these awkward and voracious little mask-wearers. The first dip of the net usually brings up a supply of dragon-fly nymphs and of their more slender cousins, the damsel-fly nymphs. The latter have expanded plate-like appendages at the hind end of the body which distinguish them from the dragon-fly nymphs.