Beetles 



259 



antennae (the long slender palpi may be at first glance mistakenly taken 

 for antennae) as members of the family Hydrophilidae, the water-scavenger 

 beetles. As the popular name indicates, these beetles feed, for the most 

 part, on decaying material, animal or plant, found in the water, although 

 they feed also on living water-plants, as Nitella; and living insects are cer- 

 tainly taken by some species. They can be distinguished from the Dyticidae 

 when swimming by their use of the oar-legs alternately, and when at the 

 surface getting air by hanging there head upward. The air spreads in a 

 thin silvery layer over the ventral side of the body, held there by fine pubes- 

 cence. 



The eggs are deposited in a ball-like silken cocoon with a curious handle- 

 like tapering curved stem or spike (Fig. 353). The cocoon floats freely 

 on the water, or is attached to some floating leaf or grass-blade or stem. 

 From fifty to a hundred eggs are enclosed in each sac. The larvae (Fig. 

 354) are elongate, but thicker and less graceful than 

 the water-tigers (larvae of the Dyticidae), and, unlike 

 the adults, feed chiefly on living insects, snails, tad- 



FIG. 352. FIG. 353. FIG. 354. 



FIG. 352. Great water-scavenger beetle, Hydrophilus triangularis. (Natural size.) 

 FIG. 353. Egg-case of great water-scavenger beetle, Hydrophilus sp. (Twice natural 



size.) 

 FIG. 354. Larva of great water-scavenger beetle, Hydrophilus caraboides. (After 



Schiodte; natural size.) 



poles, etc. They breathe through spiracles at the tip of the body, coming 

 occasionally to the surface to get air. In shallow water they simply lie 

 with the tip of the tail projected up to the surface. When ready to pupate 

 the larvae leave the water, and, burrowing a few inches into the ground, form 

 a rough cell in which they transform. The adult beetles fly readily, and 

 sometimes, with Dyticids, are to be found at night around electric lights. 

 When winter comes they burrow into the bottom or bank of the pond or 

 stream and lie torpid until spring. 



