The Water skaters, or Striders, prefer quiet waters, as do the Whirligigs, but do not have the decided social disposition, shown in the latter to such a marked degree. These Skaters, on account of their long legs and short bodies, are the "Daddy long-legs" of the water. These characteristics and their habitat make them easy to recognize. They are nervous, active insects in their movements, jumping and skimming about on the surface with but little show of grace and ease as compared with the ordinary graceful curves of the whirligigs. Their food habits are very similar to those of other surface insects, that is, dead and dying insects found floating on the water. But their method of taking food is quite different from that of the Whirligigs, because of the great difference in the structure of their mouth parts. The Whirligig, being a beetle, has the typical biting mouth parts, while the Strider has a slender beak or proboscis, by means of which it sucks the juices from its prey, as do other bugs. The fore legs are used to seize the prey and bring it within reach of the beak, The middle and hind pair are used for rowing over the surface, the latter pair, primarily, for steerage, the fine hairs on the legs making it possible, as mentioned before, to make use of the surface tension. Large dimples are formed on the surface of the water where the feet touch it. One would hardly expect it possible for an insect standing on the surface of water to get its feet dirty, yet the great care which they give to cleaning their feet clearly shows that dirt is of common occurrence, even there. The white or gray color on the lower side of the body is due to the reflection of light from minute hairs which cover the surface, and keep the insect dry even when submerged.

The marine relatives of our Striders have some curious habits. Some of them live out at sea, hundreds of miles from land, where they are thought to feed upon the dead bodies of small animals, When the surface of the sea is calm they glide in colonies quickly over the surface, showing great skill in diving, but if the sea begins to become agitated they immediately disappear from the surface.

Perhaps the most remarkable habit which a surface insect has is that possessed by some of the allies of the Skaters, which not only swim in the water, but actually run on the under side of the surface film. It would be very interesting to know how such a habit was acquired.

Another interesting group of insects are those which breathe air, as the surface film insects, yet seek their food below the surface. These insects are compelled, on account of their air-breathing habits, to repeatedly visit the surface or communicate in some way with a fresh supply of air.

We have two families of the large-sized water beetles, common in our ponds and streams. The Predaceous water-beetles and the Water-scavenger beetles. These are easily recognized, because in the former, the antennae are thread-like and not enlarged at the tip. While the members of the Water-scavenger family have the antennae enlarged or club-shaped at the tip. The Predaceous water-beetles are often quite common under electric lights, where they have been attracted by the intense light. Their large size and clumsy movements, when out of water, attract attention. But when seen in water their skill as swimmers is in striking contrast to their awkward movements made on land. The hind legs are flattened and very powerful, the surface being increased by a fringe, of strong hairs on the inner side. In swimming the stroke is made by both legs at once. Perhaps the most interesting facts about these beetles are those associated with their method of breathing.

The horny wing cases covering the abdomen are very thick and fit close against the abdomen, except at the extreme posterior end of the body. The space between the wing cases and the upper surface of the abdomen forms a large air space. The spiracles, or openings into the respiratory system, are situated at the margins of the upper side of the abdomen. When the beetle comes to the surface for a fresh supply of air it exposes the tip of the body and then by a depression of the tip of the abdomen allows a fresh supply of air to enter into the cavity below the wing covers; this cavity is then closed and the beetle is ready for another trip under the water.