208 



Usinger: Hemiptera 



bessomi and R. asphalti from the McKittrick asphalt 

 pits in what is "now very dry country around McKit- 

 trick in the western foothills of Kern County, Calif." 



Stridulation.-—k squeaking noise is produced by 

 Ranatra and is made by rubbing a thickened area at 

 the base of the front coxa along the crenulate margins 

 of the flaring coxal cavity (fig. 7:20e,/). 



Respiration. — Water scorpions are surface breathers, 

 obtaining air by means of their caudal appendages. 

 In the nymphs the respiratory tube consists of a single 

 prolongation of the abdomen with a longitudinal groove 

 which is open along the ventral surface. The adults 

 have two caudal appendages which, when held to- 

 gether, form a closed tube. The exact role of the 

 "static sense organs" is not known, but the theory 

 has been advanced that they serve for orientation 

 when the bugs descend into deep water. Most water 

 bugs have air stores which help in maintaining their 

 position in relation to the water surface. Without some 

 such "hydrostatic organ" a water bug is heavier than 

 water and hence is in danger of sinking and thus 

 losing access to the surface air which is essential 

 to its continued existence. Water scorpions, it is 

 said, utilize their "static sense organs" for orienta- 

 tion in lieu of a hydrostatic air store. 



Taxonomic characters. — The species of Ranatra are 

 distinguished mainly by differences in proportions of 

 pronotum, front femora, lateral prolongations of an- 

 tennal segments, and extension of the metaxyphus 

 between the hind coxae. The presence or absence and 

 degree of development of subapical spines on the 



Fig. 7:20. Front legs, a, Ranatra brevicol lis Montd.; b, R. 

 fused P. B.; c, egg of R. fusca P. B. dissected from a water- 

 soaked dead cattail blade; d, eggs of R. fusca P. B. in cattail 

 leaf with a part of the leaf tissue removed to expose the eggs; 



e, stridulation mechanism in Ranatra, showing ventral view of 

 head and part of prothorax. The rough patch (A) on the base of 

 coxa (C) is rubbed against the file (B) on the inner edge of the 

 anterolateral margin of prothorax (P), producing a chirping or 

 squeezing noise. Antennae (D) are partly concealed by coxae. 



f, parts of stridulatory mechanism enlarged. (Hungerford, 1922.) 



front femora provide reliable characters for some, 

 species, but the spines are variable in our species.: 

 Male genitalia have been figured by Hungerford (1922)5 

 but the differences are so slight for our species that 

 they are of little or no value in classification. 



The principal work on the taxonomy of Nepidae of. 

 North America is by Hungerford (1922). 



Key to Genera of Nepidae 



1. Body slender, subcylindrical; hind coxae approximate, 

 the intercoxal distance less than width of a coxa (fig. 

 7: 19) Ranatra Fabr. 1790 



- Body oval or elongate oval, subflattened; hind coxae 

 widely separated, the intercoxal distance much greater 

 than width of a coxa 2 



2. Broadly oval, more than 1/3 as wide as longj.propleura 

 widely separated, leaving the prosternum broadly 

 exposed posteriorly; fore femora with a longitudinal 

 trough for the reception of the tibia, the trough wider 

 on basal half than the tibia; eastern United States 



Nepa Linn. 1758 



- Elongate oval, less than 1/4 as wide as long; propleura 

 contiguous over prosternum posteriorly; fore femora 

 with longitudinal groove much narrower than tibia 

 throughout its length; southern states and Mexico 



Curicta Stal 1861 



Key to California Species of Ranatra 



1. Pronotum relatively short and broad, less than 2V£ times 

 as long, measured on the side, as width across humeri, 

 the anterior dilation of pronotum more than 90 per cent 

 as wide as head across eyes; posterior lobe much more 

 than 2/3 as long, measured on the side, as anterior 

 part, 85:100; front femur relatively broad, the proximal 

 edge of tooth located midway between apex of tro- 

 chanter and apex of femur (figs. 7:19; 7:20a); metaxphus 

 reaching nearly to base of abdomen; California, south 

 and central brevicollis Montd. 1910 



— Pronotum longer and more slender, nearly or quite 3 

 times as long as wide across humeri; the anterior 

 dilation of pronotum about 85 per cent as wide as head 

 across eyes; posterior lobe about 2/3 as long as 

 anterior part; front femur relatively slender, the prox- 

 imal edge of tooth located beyond the mid-point between 

 apex of trochanter and apex of femur; metaxyphus reach- 

 ing only 2/3 the distance to base of abdomen 2 



2. Anterior lobe of pronotum l'-4 times as long as posterior 

 lobe, measured on the side; hind femora reaching only 

 to basal third of penultimate abdominal segment (fig. 

 7:206); Lake Britton, Shasta County, California 



fusca P. B. 1805 



— Anterior lobe of pronotum relatively longer, nearly l'/£ 

 times as long as posterior lobe; hind femora reaching 

 beyond middle of penultimate abdominal segment; 

 Colorado River quadridentata Stal 1861 



REFERENCES 



BROOKE, M. M., and H. O. PROSKE 



1946. Precipitin test for determining natural insect 

 predators of immature mosquitoes. Jour. Nat. Malaria 

 Soc, 5:45-56. 

 HUNGERFORD, H. B. 



1922. The Nepidae in North America north of Mexico. 

 Kansas Univ. Sci. Bull., 14:425-469, 8 pis. 

 ORMEROD, E. A. 



1889. Ranatra linearis attacking small fish. Entomologist, 

 11:95, 119-120. 

 PIERCE, W. D. 



1948. Fossil arthropods of California. 15. Some Hemiptera 

 from the McKittrick asphalt field. Bull. S. Calif. Acad. 

 Sci., 47:21-33. 



