Water Scavenger Beetles-Hydrophilidae

Water Scavenger Beetles- Hydrophilidae

Members of the family Hydrophilidae, the water scavenger beetles, closely resemble the Dytiscidae, the predaceous diving beetles. Both are usually found in ponds, lakes, and streams, and both are oval and dark in color. The larger species in each family often grow to a length of almost two inches. The Hydrophilidae are easily distinguished from the Dytiscidae, however, by their distinctly club-shaped or claviform antennae and by their long maxillary palps.

Also, the predaceous diving beetle is a powerful swimmer whereas the water scavenger beetle, even though its streamlined shape seems perfectly designed for swimming, is a pathetic paddler. Unlike the diving beetle, which swims by beating its back legs simultaneously like a frog, the hydrophilid moves its hind legs alternately, paddling slowly along as though it were walking on dry land. What it lacks in the water, however, the water scavenger beetle makes up for in the air. It is a powerful flier.

Most hydrophilids are vegetarians, although they will sometimes feed on animal matter. Most live in aquatic environments.The exceptions to this rule belong to the subfamily Sphaeridiinae. These beetles are terrestrial, living in the dung of animals or in heaps of decomposing vegetation.

A water scavenger beetle is so equipped that when it goes beneath the surface of the water a silvery film of air spreads over the insect's ventral surface. It also has a kind of aqualung for use beneath the surface of the water-a reserve supply of air trapped beneath the wing covers. These beetles are often seen surfacing briefly to refill their air sacs.

The larvae of water scavenger beetles are usually predaceous, feeding on a variety of aquatic animals. They usually develop in the stagnant waters of ricefields, in shallow pools, or in drains. Some species, however, develop on stony substrata that are continually washed by water; others develop on dry land. Unlike the adults, the hydrophilid larvae are not equipped to carry a supply of air underwater.

A few species of water scavenger beetles, all belonging to the subfamily Hydrobiinae, are remarkable in their ability to withstand extremely high temperatures. It is therefore not surprising that these beetles are found in hot or thermal springs.

Hydrophilus piceus, the great silver water beetle, is the largest hydrophilid. Black with an olive luster, these beetles sometimes are as much as two inches in length. They are often seen flying around bright light bulbs on summer nights. They feed primarily on water plants.

Hydrophilus ccrroboides unlike H. piceus, lives on a diet of animal matter. Voracious eaters, bands of H. caraboides can strip a dead fish down to its skeleton in a matter of minutes.