198 Bugs, Cicadas, Aphids, and Scale-insects 
young are usually short-bodied, and of course wholly wingless or with small 
wing-pads only. In late autumn the water-striders conceal themselves 
in the mud beneath leaves or rubbish or at the bottom of the pool under 
roots or stones to hibernate, coming out again with the first warm days of 
spring. The whitish elongate eggs are laid in early spring, being attached 
by a sort of glue to the leaves and stems of aquatic plants. Some species 
have several generations each year. Water-striders are easily kept in 
aquaria if the sides are high enough above water to prevent their leaping 
out. In bringing them in from the pond covered pails should be used, or 
they may be enclosed in any small dry receptacle not air-tight. They are 
easily drowned if shaken about in a covered pail of water. 
A few interesting Hydrobatids, belonging to the genus Halobates (Fig. 
272), live on the surface of the ocean, especially in subtropic and tropic 
latitudes. They are said to feed on the juices of dead animals floating on 
the surface, and probably attach their eggs to floating seaweed (Sargassum). 
Certain stout-bodied insects, widest across the prothorax and with much 
shorter, stouter legs, members of the family Veliidas, are sometimes to be 
found, running about on the surface of the water, always near the shore. 
They can also run readily on land, which the true water-skaters cannot 
do. Also certain other slender insects, about J inch long, with thin long 
legs and hair-like antennae and long cylindrical head, are to be found on 
top of the water. But they creep slowly about on the surface or on the 
soft mud of the shore, and are found mostly where plants are growing in 
quiet water. These are marsh-treaders, Limnobates lineata (Fig. 273), 
and this species is the only representative of the family Limnobatidae known 
in this country. 
Swimming and diving about beneath the surface are the water-boatmen 
(family Corisidae) and back-swimmers (family Notonectidae). The water- 
boatmen (Fig. 274) are oval, finely mottled, greenish gray and black, and 
swim with back uppermost. They are all small, some only -J- inch long, 
none over half an inch. The back-swimmers have the back shaped like the 
bottom of a boat, swim with the back always down, and are usually bluish 
black and creamy white in color. Both of these kinds of water-bugs are 
predaceous, feeding on smaller aquatic creatures. But the beak of the back- 
swimmers is much longer and stronger than that of the water-boatmen, 
and can make a painful sting on one’s finger. Both kinds have the hind 
legs long and specially flattened and fringed to serve as oars, and both kinds 
come to the surface for air, although the back-swimmers come up far more 
often than the water-boatmen. The air taken up clings as a silvery bubble 
to a large part of the body both under the folded wings and on the under 
side, being held there by fine hairs which form a pile like that on velvet. 
A supply of air is thus taken down by the bugs, which enables them to remain 
