230 



Chandler: Megaloptera 



Fig. 8:1. a, adult of Sialis mohri; b, larva of Sialis sp. 

 (Ross and Frison, 1937). 



night in about nine or ten days. The larvae drop into 

 the water where their development takes place. They 

 are predaceous, seeking their prey on the bottom in 

 the mud and under stones. When the larvae are mature 

 they seek the banks above the water and burrow into 

 the ground to form an earthen cell. In this cell the 

 larval skin is shed and pupation takes place. 



Habitat and distribution. — The larvae are found in 

 well-aerated standing or running water. They are not 

 as characteristic of the riffle areas in California as 

 are the Corydalidae but may be frequently found in 

 numbers in the back eddies of streams where leaves 

 and other debris accumulate. The adults are diurnal 

 and are most active during the middle of the day. When 

 disturbed, they will often run rather than fly. Sialis 

 is found throughout the United States and well into 

 Canada, with the greatest number of species found in 

 the eastern part of the continent. 



Taxonomic characters. — The male genitalia offer 

 the principal means of distinguishing the species. 

 Although the wings sometimes present characters, in 

 general they vary too much to be of any significant 

 value, particularly since the venation often differs on 

 opposite sides of a single specimen. The sculpturing 

 of the head and pronotum is used in a few cases to 

 separate species. 



Key to the California Species of Sialis 

 Adults 



1. Females 2 



— Males 4 



2. Eighth abdominal sternite large with a long narrow 

 cleft on the apical margin (fig. 8:2a) 



nevadensis Davis 1903 



— Eighth abdominal sternite without cleft 3 



Fig. 8:2. a-c, terminal abdominal sternites of Sialis; a, nevo- 

 densis; b, rotunda; c, californica; d-e, ventral aspect of genitalia 

 and ninth segment of male Sialis; d, nevadensis; e, californica; 



f, male genitalia of S. occidens in ventral and lateral views; 



g, lateral view of head of male S. rotunda (Ross and Frison, 

 1937). 



3. Posterior margin of eighth sternite with a large, deep, 

 median depression (fig. 8:2b) rotunda Banks 1920 



— Posterior margin of eighth sternite with a median 



prominence (fig. 8:2c) 



californica Banks 1920 and occidens Ross 1937 



4. Front between the eyes with prominent hornlike process 

 (fig. 8:2^) rotunda Banks 1920 



— Front without hornlike process 5 



5. Ninth abdominal sternite produced into a flap covering 

 most of the genitalia (fig . 8:2d); northern California 

 south to Mariposa County nevadensis Davis 1903 



— Ninth sternite not produced into a flap 6 



6. Basal part of genital plate neither enlarged nor pro- 

 jecting over terminal plates; 9th sternite with fairly 

 short lateral setae; San Joaquin Valley and foothills 



arvalis Ross 1937 



— Basal part of genital plates projecting above apex of 

 terminal plate; 9th sternite with lateral setae long and 

 whiskerlike 7 



7. Genital plate with base narrow and produced into two 

 bulbous elevations (fig. 8:2e); British Columbia south 

 to northern and western California 



californica Banks 1920 



— Genital plate with base wider and not produced into 

 two bulbous knobs (fig. 8:2/); Plumas to Mariposa 

 County occidens Ross 1937 



The female of <S. arvalis Ross, described from Mokelumne 

 Hill, California is unknown. 



