Far out on the ocean, when the vessel is laboriously making her way
through the troughs and over the crests of the great waves, little birds,
black save for a patch of white on the lower back, are a common sight,
flying with quick irregular wing-beats, close to the surface of the
troubled waters. When they spy some edible bit floating beneath them, down
they drop until their tiny webbed feet just rest upon the water. Then,
snatching up the titbit, half-flying, they patter along the surface of the
water, just missing being engulfed by each oncoming wave. Thus they have
come to be named petrels--little Peters--because they seem to walk upon
the water. Without aid from the wings, however, they would soon be
immersed, so the walking is only an illusion.
But in our smallest ponds and brooks we may see this miracle taking place
almost daily, the feat being accomplished by a very interesting little
assemblage of insects, commonly called water skaters or striders. Let us
place our eyes as near as possible to the surface of the water and watch
the little creatures darting here and there.
We see that they progress securely on the top of the water, resting upon
it as if it were a sheet of ice. Their feet are so adapted that the water
only dimples beneath their slight weight, the extent of the depression not
being visible to the eye, but clearly outlined in the shadows upon the
bottom. In an eddy of air a tiny fly is caught and whirled upon the water,
where it struggles vigorously, striving to lift its wings clear of the
surface. In an instant the water strider--pirate of the pond that he
is--reaches forward his crooked fore legs, and here endeth the career of
the unfortunate fly.
In the air, in the earth, and below the surface of the water are hundreds
of living creatures, but the water striders and their near relatives are
unique. No other group shares their power of actually walking, or rather
pushing themselves, upon the surface of the water. They have a little
piece of the world all to themselves. Yet, although three fifths of the
earth's surface consists of water, this group of insects is a small one. A
very few, however, are found out upon the ocean, where the tiny creatures
row themselves cheerfully along. It is thought that they attach their eggs
to the floating saragassum seaweed. If only we knew the whole life of one
of these ocean water striders and all the strange sights it must see, a
fairy story indeed would be unfolded to us.
However, all the Lilliputian craft of our brooks are not galleys; there
are submarines, which, in excellence of action and control, put to shame
all human efforts along the same line. These are the water boatmen, stout
boat-shaped insects whose hind legs are long, projecting outward like the
oars of a rowboat. They feather their oars, too, or rather the oars are
feathered for them, a fringe of long hairs growing out on each side of the
blade. Some of the boatmen swim upside down, and these have the back
keeled instead of the breast. Like real submarine boats, these insects
have to come up for air occasionally; and, again like similar craft of
human handiwork, their principal mission in life seems to be warfare upon
the weaker creatures about them.
Upon their bodies are many short hairs that have the power of enclosing
and retaining a good-sized bubble of air. Thus the little boatman is well
supplied for each submarine trip, and he does not have to return to the
surface until all this storage air has been exhausted. In perfectly pure
water, however, these boatmen can remain almost indefinitely below the
surface, although it is not known how they obtain from the water the
oxygen which they usually take from the air.
All of these skaters and boatmen thrive in small aquariums, and if given
pieces of scraped meat will live in perfect health. Here is an alluring
opportunity for anyone to add to our knowledge of insect life; for the
most recent scientific books admit that we do not yet know the complete
life history of even one of these little brothers of the pond.
Clear and cool, clear and cool,
By laughing shallow, and dreaming pool;
Cool and clear, cool and clear,
By shining shingle, and foaming weir,
Charles Kingsley.