the swiftest part of the stream. Some are found in the 

 larger streams, often in immense masses, making a 

 mosslike covering over rocks, but many others are 

 found in the more rapidly flowing parts of very small 

 water courses. They attach by means of a posterior 

 sucker, with their heads pointed downstream, and 

 they move about by a looping movement involving this 

 posterior sucker and a median prothoracic leg, and 

 also by means of silken threads which they can let 

 out, permitting them to move rapidly without being 

 swept completely away. In all but the far northern 

 genus Gymnopais, the larva possesses a pair of 

 large mouth brushes which are spread out to strain 

 the water for food particles. The body is soft and 

 sacklike, widest near the posterior third, and when 

 fully grown, the darkened histoblasts of the develop- 

 ing respiratory organs of the pupa can be seen at the 

 sides of the thorax. 



The larva spins a cocoon (fig. 14:19n,p), attaching 

 it to the surface on which it rests. In Pro sirnulium 

 and some Cnephia species this is loose and irregular 

 and may cover the respiratory organs anteriorly. In 

 most other species, however, this cocoon is a well- 

 defined wall-pocket or boot- shaped structure, often 

 possessing characters of value in specific identifica- 

 tion. The pupa lies in the cocoon with the variously 

 formed thoracic respiratory organs partly protruding 

 from the anterior downstream opening of the cocoon. 

 The adult emerges in an air bubble if the cocoon is 

 still under water at the time of emergence, and the 

 adults can fly immediately. 



The adults may occur in huge numbers and since 

 the reaction to the bite is often very severe, they 

 can cause serious losses to livestock, wild mammals, 

 and birds. Some species carry onchocerciasis, a 

 filarial disease of man in the tropics, and others 

 transmit blood diseases of birds. 



Keys to the North American Genera of Simuliidae 

 Adults 



1. A bulla behind eye laterally; scutum with stout erect 

 hairs but no fine recumbent hairs Gymnopais Stone 



— No bulla behind eye; scutum usually with fine recum- 

 bent hairs but never with stout, erect ones 2 



2. Macrotrichia of anterior wing veins hairlike, not inter- 

 mingled with spiniform ones 3 



— Macrotrichia of anterior wing veins mixed hairlike and 

 spiniform (fig. 14:19c) 4 



3. Vein Rj joining costa at about middle of wing 



Parasimulium Malloch 



— • Vein R x joining costa well beyond middle of wing (fig. 

 14:196) Prosimulium Roubaud 



4. Second hind tarsal segment without a distinct notch 

 (pedisulcus) dorsally near base-; vein R with hairs 

 dorsally Cnephia Enderlein 



— Second hind tarsal segment with a distinct pedisulcus 

 (fig. 14:19<i); vein R usually without hairs dorsally 



Sirnulium Latreille 



P upae 



1. Dorsum of abdomen with no hooks; sternites 4-6 each 

 with about 10 hooks in more than one transverse row; 

 almost no cocoon Gymnopais Stone 



403 

 Wirth and Stone: Diptero 



— Dorsum of abdomen with books on soma of the 

 ments; if sternites 4-6 have more than 1 hoot, tl 

 are in a single transverse row 2 



2. Strong terminal hooks present; cocoon irrei^ular without 

 any clearly defined anterior margin; respirator] fila- 

 ments if fewer than 14 not arising from more than 2 main 

 trunks; if more than 14 not arising from a rounded knob 

 on a short petiole Prosimulium Roubaud 



— Terminal hooks usually very weak or absent and cocoon 

 well formed and with a clearly defined anterior margin; 

 if not, the respiratory organ of about 11 filaments 

 arising at a considerable distance from the base from 

 2 main trunks, or the filaments more numerous, arising 

 from a rounded knob on a short petiole '■'• 



3. Either terminal hooks well developed and cocoon poorly 

 formed or cocoon with a broad anteroventral collar so 

 that it is boot-shaped and tergites 5-7 each have an 

 anterior row of small spines Cnephia Enderlein 



— Terminal hooks weak or absent; cocoon well developed; 

 either cocoon is boot-shaped with a series of loops 

 forming the anterior margin (fig. 14:19p) and tergites 

 5-7 are free of spines anteriorly, or the cocoon is 

 wall-pocked-shaped Sirnulium Latreille 



The pupa of Parasimulium is not known. 



California Species of Simuliidae 



Genus Parasimulium Malloch 



This is an unusual genus known only from a single 

 male specimen collected at Bair's Ranch, Humboldt 

 County, and described by Malloch (1914) as Para- 

 simulium furcatum. Discovery of the immature stages 

 would be of very great interest. 



Genus Prosimulium Roubaud 



Species of this genus appear to have only one emer- 

 gence in a season, and most of them appear rather 

 early in the spring or summer. The pupae are often 

 found in dense masses on sticks and stones. There 

 is no evidence that any of the California species are 

 annoying as pests of man, as is Prosimulium hirtipes 

 in the North and East. There are at least four unde- 

 scribed species in California in addition to those 

 listed here. These will not run to any of the species 

 in the pupal key here given, but cannot be separated 

 from all those given in the adult keys. 



Keys to California Species of Prosimulium 

 Females 



1. Claws bifid; that is, with the basal swelling produced 

 into a strong, acute tooth; mesoscutum predominately 

 reddish brown; Calaveras County 



onychodactylum Dyar and Shannon 1927 



— Claws simple, with not more than a basal swelling or 

 with a very minute basal tooth adjacent to the basal 

 swelling 2 



2. Integument orange; Plumas and Marin counties to Tulare 

 County fulvum (Coquillett) 1902 



— Integument dark brown to black 3 



3. Antenna with 9 segments; Plumas County 



novum Dyar and Shannon 1927 



— Antenna with 1 1 segments 4 



