A few busy Mosquito Hawks, or Dragon flies (Libellula), herald the coming of the summer brood of these indefatigable friends of the agriculturist. During their whole life below the waters, these entomological Herods have slain and sucked the blood of myriads of infant mosquitoes and other insects; and now in their new world above the waters, with still more intensified powers of doing mischief, happily, however, to flies mostly obnoxious to man, they riot in bloodshed and carnage. [Illustration: 234. Different Forms of Case Worms.] This is the season to stock the fresh-water aquarium. Go to the nearest brook, gather a sprig or two of the water cress, which spreads so rapidly, a root of the eel grass, and plant them in a glass dish or deep jar. Pour in your water, let the sand and sediment settle, and then put in a few Tadpoles, a Newt (Salamander), Snails (Limnaea, Planorbis and Valvata), Caddis flies and Water beetles, together with the gatherings from a thicket of eel grass, or other submerged plants, being rich in the young of various flies, Ephemeras, Dragon flies and Water fleas (Entomostraca, Fig. 235), which last are beautiful objects for the microscope, and in a few days the occupants will feel at home, and the aquarium will be swarming with life, affording amusement and occupation for many a dull hour, by day or at night, in watching the marvels of insect transformations, and plant-growth. Among the injurious hymenoptera, which abound late in this month, is the Rose Saw fly (Selandria rosae, Fig. 236) and S. cerasi. The eggs are then laid, and the last of June, or early in July, the slug-like larvae mature, and the perfect insects fly in July. Various Gall flies now lay their eggs in the buds, leaves and stems of various kinds of oaks, blackberries, blueberries and other plants. [Illustration: 235. Water Flea.] [Illustration: 236. Selandria rosae.]