2 m 



Fig, 13:49. Dryopidae. a, Hel ichus suturalis, adult; b, Dryops 

 sp., antenna; c, Helichus immsi, dorsal and lateral view of male 

 genitalia; d, Helichus produclus, dorsal and lateral view of male 

 genitalia; e, Helichus strialus, lateral and dorsal view of male 

 genitalia; f, Helichus suturali s, lateral and dorsal view of male 

 genitalia (a,c,d, Hinton, 1937; b, Hinton, 1939; e,f, Musgrave, 

 1935). 



on the mesothorax and the first seven abdominal 

 segments and a pair of dorsal spiracles on the eighth, 

 but it is not known if any of these are functional. 

 Dryops luridus Erichson from Europe, which is aquatic 

 but has been reported also from damp soil, is entirely 

 surrounded by a film of air when submerged. The 

 integument has a smooth, glassy texture. The habitat 

 of the larva of D. arizonensis is not known. The larva 

 of Pelonomus is similar in appearance to D. luridus. 

 Helichus larvae have two large, irregular, raised 

 patches of microscopic hydrofuge pile on each of the 

 segments with lateral spiracles; the spiracle is on 



355 

 Leech and Chandler: Coleoptera 



the anterior margin of the narrow isthmus between the 

 two patches. The enlarged dorsal pair of spiracles on 

 the eighth abdominal aegment arc < I. ether and 



in a position to suggest that the) ma\ be used for 

 surface breathing. 



Life history. — Little is known of the life history of 

 these beetles. The adults of Helichus are abundant in 

 many places, yet only two larvae are known to have 

 been collected in the United States. They were col- 

 lected in north central California from a very small 

 and a medium-sized creek about a mile apart. Both 

 were taken from swift, turbulent water by turning 

 rocks and agitating the Ixittom. The shape of the last 

 abdominal segment suggests a burrowing habitat. Lar- 

 vae of Pelonomus were found by Sanderson in a damp 

 flood-plain depression. The pupa of Dryops luridus 

 is terrestrial. 



The adults feed on vegetation at the bottom of 

 streams, but the larvae are believed to be root feeders. 

 Although the wings are well developed I have never 

 seen the adults in flight. They are widely distributed 

 in desert areas indicating dispersal by this method. 

 1 found several adults of two species in a large open- 

 top steel water-storage tank for a stock-watering 

 trough. The water was supplied from a well by a 

 windmill driven pump. It was about fifteen miles from 

 this tank to the nearest stream. 



Habitat and distribution. — The Dryopidae are found 

 mostly in the tropical and warmer temperate regions 

 of the world with an occasional species extending 

 into the cooler regions. Dryops is found on every 

 continent except Australia. Pelonomus is from south- 

 eastern United States. Helichus is found in Mexico 

 and most of the United States, with H. lithophilus in 

 the east and //. foveatus in the west extending into 

 Canada. In California it is found in moderately to 

 rapidly flowing creeks or rivers with rocky or gravel 

 bottoms, from sea level up to an elevation of 6,000 

 feet. H. suturalis ranges from Mexico to northern 

 California and southern Utah. 



Taxonomic characters. — The placement and form of 

 the antennae serve to separate the Nearctic genera 

 but cannot be relied on in other parts of the world. 

 In Helichus pubescence is the most used character 

 since it covers most of the body, masking many other 

 possible characters. It should always be used with 

 discretion since the specimen may assume quite a 

 different appearance if it is rubbed off or soiled with 

 grease or dirt. If one is not familiar with the group, it 

 is best to check the male genitalia, especially with 

 H. productus, H. immsi, and several related species 

 found in Arizona, New Mexico, Texas, and Mexico, 

 for which no dependable distinguishing characters 

 have been found. Size and slight differences in shape 

 are of limited usefulness and difficult to describe. 

 There is a tendency in H. foveatus for alternate 

 interstrial spaces to be more convex. Several species 

 and subspacies have been based largely on the pres- 

 ence or lack of this character, but study of specimens 

 from many localities indicates that it is of minor 

 importance. H. suturalis is also very variable and is 

 reported by Hinton to have the number of antennal 

 segments sometimes reduced owing to the fusing 



