damp earth, and posterior cerci which enable it to 

 move around. Since there is no covering of hydrofugc 

 hair, the thoracic and abdominal spiracles cannot be 

 kept dry, and the pupa is readily drowned if water 

 enters its cell. Mature larvae of some species of 

 Enochrus are said to form pupal cases in the water 

 by tying algae together. 



Parasites. — Several species of nematode worms 

 have been recorded as parasites of Old World hydroph- 

 ilids (adults). Todd (1942) described a new genus 

 and species of nematode, Zonothrix tropisterna, from 

 Tropisternus lateralis nimbatus (Say) from Nebraska; 

 in 1944 he described two new species, P seudonymus 

 brachycercus and P. leptocercus from Hydrophilus 

 triangularis (Say) from Nebraska and Louisiana; all 

 worms were in the large intestine. Wilson (1923) 

 records hymenopterous larvae from a H. triangularis 

 larva in its pupal cell. 



Habitat and distribution. — The larvae of most spe- 

 cies are aquatic, or live in wet sand or soil at the 

 waters edge; those of the Sphaeridiinae are in dung, 

 wet rotting vegetable matter (especially cacti), or 

 under dead leaves in damp places near the water. 

 Of the aquatic larvae, all but Berosus spp. are found 

 in shallow water, usually among algae and weeds, or 

 in the marginal debris. 



None of the New World species has been reported 

 as an agricultural pest, but in England two kinds of 

 Helophorus, both larvae and adults, attack turnips, 

 cabbages, swedes, and other cruciferous crops; in 

 Russia a species of Helophorus is said to damage 

 grasses. At least three species of predaceous Dacty- 

 losternum have been used in attempts to control the 

 sugar cane beetle borer in the Philippine Islands and 

 Hawaii, and one against the banana borer in Jamaica. 



Adult hydrophilids are commonest in marshy places, 

 in weedy, shallow ponds, or in flooded areas where 

 there is grass growing out of the water. Some species 

 prefer saline or mineralized waters; others occur in 

 running water, especially where algae grow. 



The family Hydrophilidae is comparable to the 

 Dytiscidae in number of species, but has been less 

 studied. The dytiscids are more numerous in the 

 colder parts of the world, the hydrophilids in the 

 warmer; this applies especially to the terrestrial 

 Sphaeridiinae. All the subfamilies and a majority of 

 the tribes are represented in the North American 

 and even in the California fauna. 



Taxonomic characters. — Body form is usually char- 

 acteristic, and except the smallest, most North 

 American species can be placed to genus at sight. 

 Color is of specific value in a few genera, and is 

 correlated somewhat with generic recognition (that is, 

 metallic colors are rare except in Helophorus, Hydro- 

 chus, and Berosus), but most hydrophilids are so 

 uniformly unicolorous that a color pattern is rarely 

 available. The punctation and/or striation of the ely- 

 tra, punctation of the head and pronotum, forms of 

 the elytral apices (Berosus), form and punctation of 

 the pro-, meso-, and metasternum (Sphaeridiinae, 

 Hydrophilinae, Hydrobiinae), and extent of hydrofuge 

 pubescence on the ventral surface (Hydrophilinae, 

 Hydrobiinae) are the chief characters of value. 



337 

 Leech and Chandler: Coleoptera 



The sexes are often difficult or impossible to 

 separate on external features, hut males of some 

 species are distinguished by enlarged or peculiarly 

 shaped front and middle tarsal claws, curved or 

 otherwise modified tibiae, cristate abdominal ster- 

 nites, and different!}, punctate mesosternal areas. 



Key to the Genera of Hydrophilidae 



of the United States and Canada 



Adults 



1. Pronotum with 5 longitudinal grooves (fig. 13:3 1a), 

 or produced anteriorly at middle so as to hide much 

 of head (fig. 13:3 \c) 2 



— Pronotum not with 5 longitudinal grooves, not produced 

 anteriorly to hide much of head 3 



2. Pronotum with 5 longitudinal grooves; antennae short, 

 9-segmented, not compact; eyes not divided by a 

 canthus; form more or less elongate, not very convex, 

 elytra not projecting below abdomen. HELOPIIORINAE 

 (fig. 13:306) Helophorus Fabricius 1775 



— Pronotum without longitudinal grooves, but produced 

 anteriorly at middle, covering much of head; antennae 

 9-segmented, club pubescent, compact; eyes divided 

 horizontally, partly or completely, by a canthus; form 

 short and convex, elytra projecting much below abdomen. 

 EPIMETOPINAE (fig. 13:3 \c) 



Epimetopus Lacordaire 1854 



3. Pronotum conspicuously narrower than elytral bases; 

 scutellum very small, eyes protuberant; maxillary 

 palpi never very long; antennae with no more than 3 

 segments before the cupule. HYDROCHINAE (fig. 

 13:3 Id) Hydrochus Leach 1817 



— Pronotum not appreciably narrower than elytral bases 

 (except in some Berosini, but there note elongate 

 triangular scutellum); eyes prominent or not; antennae 

 usually with 5 well-developed segments before the 

 cupule 4 



4. Basal segment (which may be very small) of hind tarsi 

 shorter than 2nd; antennae shorter, about as long as 

 or shorter than maxillary palpi (fig. 13:36a); last 

 glabrous antennal segment asymmetrical, often cuplike, 

 embracing 1st segment of pubescent always triarticulate 

 club; 2nd segment of maxillary palpi not or little 

 thicker than 3rd or 4th; aquatic species 5 



— 3asal segment of hind tarsi longer than 2nd segment; 

 antennae usually longer than maxillary palpi which 



Fig. 13:36. Hydrophilidae, adults, a, Hydrophilus triangu- 

 laris; b, Hydrobius fuscipes (a, Borror and Delong, 1954; fa, 

 Miall, 1903). 



