THE HYDROPHILID& 



313 



hind legs adapted for swimming, like the Dyticidae, from which the species are distinguished by 

 their herbivorous habits, besides the fundamental differences in their antennae and niouth organs. 



The tribe consists of one family only (HYDROPHILID.E), containing five sub-families, of which 

 four are water-insects, and the fifth, the Sphaeridiinae, live on the dung of land animals. The 

 aquatic series comprises the fine genus HYDROPHILUS, which vies with Dyticus in the size of its 

 species. Hydrophilus piceus is a well-known inhabitant of our ponds, and one of the largest of the 

 British Beetles. It is of more convex form than any species of Dyticus, and distinguished from them 

 also by its uniform deep 

 black colour, and its less 

 energetic motions in the 

 water. Its mode of taking 

 a supply of air is totally 

 different from that of the 

 Dyticidae; for whilst the 

 latter protrude the hind 

 extremity of the body 

 above the surface, the 

 Hydrophilus elevates its 

 head, and by a peculiar 

 movement of the antennae 

 above the water, makes 

 the air descend along the 

 pubescent joints of the 

 club, and thence to the 

 fine hairs which clothe the 

 flanks of the thorax, which 

 pass it on to the stigmatic 

 openings of the breathing 

 tubes. There are some 

 important differences, also, 

 in the habits of the female 

 insects with regard to 

 the preservation of their 

 offspring. The mother 

 Hydrophilus weaves, by 

 means of a tenacious fluid 

 secreted by two spinnerets 

 in the anus, a kind of 

 cocoon, which she attaches 

 to the under-surface of 

 the leaf of some aquatic 

 plant near the surface of 

 the water, and which is 

 provided with a tube 



rising above the surface, destined to introduce a supply of air to the interior. In this cocoon 

 she lays her eggs, to the number of about fifty, enveloped with a cottony substance. The larvae 

 emerge from the bottom of the cocoon at the end of six weeks, and swim forth in search of 

 food; and it is remarkable that, instead of being vegetable feeders like their parents, they are 

 carnivorous, and of extreme voracity. They are somewhat similar to the larvae of Dyticus, 

 but much thicker and more fleshy, covered with leathery, finely-shagreened skin, and the mandibles 

 are toothed. Like the Dyticidae, they crawl out of water to undergo their transformation into the 

 pupa, and thence into the adult Beetle, burying themselves for the purpose in the damp ground. 



The keel-shaped ridge running down the middle of the sternum of this insect, on the under side 

 230 



HVDROPHILFS PICEUS. 



