Typical Adult Stonefly and Cast Nymphal Skin (Courtesy of Dr. E. S. Ross, California Academy of Sciences) BULLETIN OF THE CALIFORNIA INSECT SURVEY VOLUME 6, NO. 6 THE STONEFLIES (PLECOPTERA) OF CALIFORNIA BY STANLEY G. JEWETT, JR (U.S. Bureau ofCommercia1 Fisheries, Portland, Oregon) UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES l%O BULLETIN OF THE CALIFORNIA INSECT SURVEY Editors: E. G. Linsley, S. B. Freeborn, P. D.Hurd, R. L. Usinger Volume 6, No. 6, pp. 125 - 178,41 figures in text, frontis. Submitted by Editors, February 10,1959 Issued June 17, 1960 Price $1.25 UNIVERSITY OF CALIFORNIA PRESS BERKELEY AND LOS ANGELES CALIFORNIA CAMBRIDGE UNIVERSEY PRESS LONDON, ENGLAND PRINTED BY OFFSET IN THE UNITED STATES OF AMERICA THE STONEFLIES (PLECOPTERA) OF CALIFORNIA BY STANLEY G. JEWETT, JR. INTRODUCTION cipally vegetarian and the Setipalpia mostly car- nivorous - both the physical character of the Plecoptera is a relatively small order of aquatic aquatic environment and its biota govern the kinds insects with a world fauna of approximately 1,200 of stoneflies which occur in a habitat. Much valu- species. They require moving water for develop- able work could be done in determining the eco- ment of the nymphs, and for that reason the adults logical distribution of stoneflies in California, are usually found near streams. In some northern and the results could have application in fishery regions their early life is passed in cold lakes management and pollution studies. where the shore area is composed of gravel, but In general, the stonefly fauna of the western in most areas the immature stages are passed in cordilleran region is of similar aspect. Of the creeks and rivers. There is a marked seasonal 101 species recorded herein for California, 73 succession in the emergence of stoneflies, par- occur in Oregon, and 60 are recorded for British ticularly in the northern hemisphere; adult stone- Columbia. As further collecting is done in west- flies can be collected every month of the year in ern North America, indications of an even greater California if the proper locality is visited. homogeneity in the Plecopteran fauna can be ex- Adult members of the genus Btachyptera are pected than these records indicate. Nevertheless, occasionally an agricultural pest to soft fruit existing records show that many species have a crops in the Pacific Northwest, where they are limited range and that distinctive differences oc- reported to feed on the tender buds of these plants cur in the stonefly fauna of different regions with- (Newcomer, 1918). The principal economic im- in western North America. For example, the coast- portance of the majority of species, however, lies al area of central California has at least three in their beneficial value as food for fish. Dimick unique species that probably occur only in that and Mote (1934) rat e stoneflies as the second area. Several northern species are holarctic, but most important order of insects in the diet of none of these reaches California. Several stone Oregon rainbow trout that are resident in streams. flies are w i des p read in North America among Stoneflies require a habitat with cool, well- which are Taeniopteryz mawa(Pictet)and Leuctra oxygenated water. The temperature of the water swa Claassen, both of which occur in eastern controls development and emergence; streams with North America and in California. Table 1 indi- marked temperature changes during the seasons cates present records of California stoneflies by usually display a distinctive sequence of emer- counties. gence of various species. Springs and streams The world stonefly fauna includes nine fami- of constant or nearly constant temperature do not lies (Ricker, 1951), three of which are primarily have a distinctive succession of forms; the spe- Notogaeaa. Six occur in North America, and all cies frequenting such habitats emerge during a of these are represented in California. There are period of many months. Some stoneflies occur approximately 350 d e s c r i bed North American only in large streams; some are found solely in stoneflies. As the fauna of this state becomes small streams; still others frequent a wide range better known, the present list of 101 species will of stream sizes. Since they differ in their Eeed- probably be increased. ing habits - the suborder Filipalpia being prin- In addition to my material (S.G.J.), the cob 126 BULLETIN OF THE CALIFORNIA INSECT SURVEY lections of the California Academy of Sciences primarily diurnal, but many Setipalpia are crepus- (C.A.S.), the California Insect Survey (C.I.S.), cular or nocturnal and are attracted at night to the University of California at Los Angeles artificial lights. (U.C.L.A.), D. L. Abell (D.L.A.),the late Harry Egg. - Eggs are most frequently deposited in P. Chandler (H.P.C.), Steph en W. Hitchcock flight over water, but so m e species, notably (S.H.), and Wm. E. Ricker (W.E.R.), have provided among the Filipalpia, crawl to the water’s edge the majority of the records for California stone- for egg deposition. A stonefly may lay eggs only flies. A few specimens which I have collected once or several times. In some species the total have been deposited in the United States National number of eggs deposited by one stonefly is Museum (U.S.N.M.). Permission to examine the known to exceed a thousand. Egg shape usually material and record specimens in these collec- differs in the two suborders: those of the Fili- tions is gratefully acknowledged. palpia are spherical in general shape and have a Adult. - The adult stonefly is readily distin- sticky coating w h en moistened, an adaptation guished from other insects with which it might be which enables them to adhere to the substrate; confused, such as male Embioptera and certain those of the Setipalpia are usually longer than Neuroptera, by its relatively primitive venation wide but variously shaped and sculptured, with- and mouth parts and by the fact that stoneflies out an adhesive coating but with an anchor plate. always have three tarsal segments and two or Nymphs.- The nymphs of European stoneflies three ocelli. Stoneflies vary in body length from and those found in the midwestern United States 4-5 mm. (small Capnia and Nemowa) to 40-50 mm. are rather well known, but those of a great many (large Pteronmcys). Most stoneflies are normally North American species have not yet been de- winged, but a number are known to be brachypter- scribed; this is particularly true of our western ous. One little-known western species, recorded species. Many stonefly nymphs occur in waters only from New Mexico, is apparently wingless in with a gravel bottom, but soae species are found the male (Capnia fibula Claassen); this is also where the substrate is chiefly detritus. Generally, true of another Capniid found in the Midwest, the Filipalpia are found most abundantly in cooler AZlocapnia vidpara (Claassen). Filipalpia are waters, and the Setipalpia, most commonly in FiK. 1. Bmciiyptera pacifica. a, adult female; b, mandibles in ventral view; c, female terminal abdominal seEmencs; d, labium; e, maxilla; f, hbrum. dorsally at left and ventrally at right (Newcomer, 1918). THE STONEFLIES (PLECOPTERA) OF CALIFORNIA 127 warmer waters. Many exceptions occur, and in a pair of forceps. During the rest of the year the some tropical regions only Setipalpia are found. most productive method of collecting is by sweep- For the stoneflies which have been reared from ing vegetation along streams with an insect net. eggs, the number of instars has varied from The foliage of conifers is a favorite resting place twenty-two to thirty-three (Claassen, 1931, pp. for stoneflies w h e rev e r those trees bo r d e r 7-8). Development of the nymph may occur grad- streams. Nocturnal species may be taken at arti- ually, but in the majority of species there is ap- ficial lights, from under large stones bordering parently a period shortly after hatching when streams, and particularly from under loose bark growth virtually ceases (Brinck, 1949, pp. 131- of logs which extend into the water. Cast nymphal 140). The nymphal stage lasts about a year in skins found on rocks or tree trunks near the water most species, but two or three years are required should be preserved. in some. Nymphs may or may not have external Nymphs are easily collected by overturning gills on the mentum, submentum, neck, thoracic rocks and stirring gravel in stream beds upstream segments, or on the first few abdominal segments, from the opening of an aquatic net of fine-meshed or gills may be extruded from the anus. Remnants sieve. An excellent source of nymphs is among of nymphal gills are present on some adults and the debris which collects at grills at water diver- ace important in classifying the order. sion structures. Nymphs may be reared by plac- The keys presented here have been modified ing them in small wire cages fixed to a floating from those prepared for my chapter on Plecoptera raft in streams in such a manner that the upper in Usinger et d. (19%). As indicated in that part of each cqe is above the water level (Fri- study, most of the keys have been adapted from son, 19334 pp. 305-307). those devised by Claassen (1931), Frison (1935, 1942), Needham and Claassen (1925), and Ricker (1943, 1952). Illustrations have been reproduced TAXONOMIC CHARACTERS from published figures. Literature citations for each species include the original descripaon, the Wing venation, gills, number of ocelli, and male reference in Needham and Claassen's 1925 mono- genitalia are the principal morphological features graph if included in that work, and synonyms and systematic references occurring subsequent to 1925.