their lack of scales and the curvature of the apical 

 wing veins. The larvae resemble those of anopheline 

 mosquitoes, except that the thoracic segments are 

 not fused into a broadened body, one or two pairs of 

 prologs are present on the abdomen, and the caudal 

 appendages are quite different. 



The adult flies are usually found resting on the 

 shaded side of rocks a few inches above the surface 

 of streams or ponds, always facing upward. It is not 

 known whether there is any feeding in the adult stage. 

 The dixids do very little flying during the day, but 

 in the evening the males may form small mating 

 swarms, which are apparently oriented opposite vege- 

 tation overhanging the water. Mating can occur in 

 flight or on the rocks bordering the stream. The eggs 

 are laid in a mass of jelly on a solid substratum 

 above the water line. 



The larvae always occur along the downstream 

 margin of rocks or floating branches. They may be 

 divided into at least two groups on the basis of their 

 habits. Those of the subgenus Meringodixa lie on the 

 surface of the water with their bodies at right angles 

 to the substratum, the caudal end being in the menis- 

 cus and the head directed away from the substratum. 

 The larvae of Dixa and Paradixa assume the typical 

 inverted-U position at or just above the water surface 

 with the head and caudal end in the water. The latter 

 group can crawl about on the rocks by sliding on a 

 film of water pushed ahead of them. The larval food 

 of the Dixidae is believed to consist of microscopic 

 organisms in the surface film. The pupae (fig. 14:18o) 

 are found attached by their sides to the substratum as 

 much as two inches above the water. 



Recently Nowell (1951) published a large study of 

 the family in western North America in which he 

 recognized three subfamilies and eight genera. The 

 larvae of the California species can easily be divided 

 into three morphological groups, but the adults of 

 Dixa and Meringodixa are difficult to separate. There- 

 fore it does not seem advisable to recognize them 

 as full genera at this time. The species are all very 

 similar in appearance, and many of them can be 

 separated only by a study of the male genitalia. The 

 California species are not well enough known for 

 keys to be presented, particularly since, in a period 

 of two years Johannsen (1923, 1924), Dyar and Shan- 

 non (1924), and Garrett (1924) published papers on 

 western species, and considerable synonymy is 

 involved. 



Keys to California Subgenera of Dixa 

 Larvae 



1. One pair of abdominal prolegs (fig. 14:18,/) 



Meringodixa Nowell 1951 



— Two pairs of abdominal prolegs (fig. 14:18c) 2 



2. Dorsum of abdomen bare or nearly so (fig. \i:\8d) 

 Paradixa Tonnoir 1924 



— Dorsum of abdomen with rosettes of hairs on segments 

 2 to 7 Dixa Meigen 1818 



401 

 Wirth and Stone: Diptera 



Adults 



1. Sternopleura bare; 1st flagellar sogmont of antenna 

 cylindrical Paradixa 



— Sternopleura with at least a few hairs; 1st flagellar 

 segment of antenna fusiform 2 



2. First flagellar segment of antenna 6 times as long as 

 broad Meringodixa 



— First flagellar segment of antenna 4 times as long as 

 broad Dixa 



California Species of Dixa 



Dixa (Dixa) hegemonica Dyar and Shannon 1924. Humboldt 



County 

 Dixa (Dixa) modesta Johannsen 1903. Riverside County 



Dixa (Dixa) rhathyme Dyar and Lake, 



Shannon 1924. Santa Clara, Ventura counties 



Dixa (Dixa) xavia Dyar and Lake County to 



Shannon 1924. Santa Clara County 



Dixa (Meringodixa) chalonensis San Benito County 



Nowell 1951. 

 Dixa (Paradixa) aliciae Santa Clara and 



Johannsen 1924. Merced counties 



Dixa (Paradixa) calif ornica Humboldt to Monterey 



Johannsen 1923. and Tulare counties 



Dixa (Paradixa) somnolenta Dyar Tulare County 



and Shannon 1924. 



REFERENCES 



DYAR, H. G. and R. C. SHANNON 



1924. Some new species of American Dixa Meigen. Insec. 

 Inscit. Menst., 12:193-201. 

 GARRETT, C. B. D. 



1924. New American Dixidae. Privately published at 

 Cranbrook, B.C. 

 JOHANNSEN, O. A. 



1923. North American Dixidae. Psyche, 30:52-58. 



1924. A new species of Dixa from California. Psyche, 

 31:45-46. 



1934. See Diptera references. 

 KELLOGG, VERNON L. 



1905. American Insects. 

 NOWELL, W. R. 



1951. The dipterous family Dixidae in western North 

 America (Insecta: Diptera). Microentomology, 16:187- 

 270, figs. 74-88. 



Family SIMULIIDAE 



Black flies, sometimes known as buffalo gnats or 

 turkey gnats, are small, usually dark, compactly built 

 flies (fig. 14:19z,/) with a rounded back and short, 

 broad wings, with the heavy veins concentrated near 

 the anterior margin of the wing. The antennae are 

 nine- to eleven-segmented, rather short and stout 

 with no long hairs. The females of most of the species 

 are bloodsucking, and certain species attack man 

 readily, but others prefer domestic animals or birds. 

 They feed during the daylight hours and sometimes 

 into the night, and adults, particularly the males, are 

 collected readily at light traps. Many species will 

 fly considerable distances from the breeding areas. 

 The larvae (fig. 14:19a) are found in flowing water 

 on stones, vegetation, or other objects, usually in 



