skin. So immense are the numbers of insects which
fill the air and enliven the fields and woodlands just as summer comes
in, that a bare enumeration of them would overcrowd our pages, and tire
the reader.

[Illustration: 233. May Fly.]

A word, however, about our water insects. Late in the month the May fly
(Ephemera, Fig. 233) appears, often rising in immense numbers, from the
surface of pools and sluggish brooks. In Europe, whole clouds of these
delicate forms, with their thin white wings, have been known to fall
like snow upon the ground, when the peasants gather them up in heaps to
enrich their gardens and farms.

The Case worms, or Caddis flies (Fig. 234), begin now to leave their
portable houses, formed of pieces of leaves, or sticks and fine gravel,
or even of shells, as in an European species, and fly over the water,
resting on the overhanging trees.

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