158 



University of California Publications. [Entomology 



ment, anterior and extends into water, anal siphon protrudes. 

 Pupa (young) white, naked; mouth parts pressed to the breast, 

 indistinguishable; legs folded along the abdomen, head high 

 between the eyes; wings reach to tarsi of second pair of legs. 

 (Fig. 104.) 



Note. — These flies have become very abundant along the 

 southwest shore of San Francisco Bay between the small towns 

 of San Mateo and San Bruno, the center of the colony seem- 

 ing to be about Millbrae, where the floating puparia and adults 



PIG. 105. Eplujiira miUbru:. 



a. Head from above. 6. Thorax from above, showing position of spines, 

 abdomen of female, il . End of abdomen of male. 



c. End of 



often cover the entire surface of the small salt-Avater ponds. 

 Like mosquitoes, they seem unable to breed in water afl^ected 

 by the tide, but prefer the smaller pools that are practically 

 without motion. The salinity of these marshes, owing to 

 gradual evaporation during the summer and autumn months, 

 often becomes much greater than that of the bay itself. I 

 have found the flies living in ponds where the salinity was as 

 high as 4.2 per cent, being almost one per cent higher than 

 that of the average sea water. The migratory propensities do 

 not seem to be very great and the immense colonies move about 

 from pond to pond only as compelled by the absolute drying 

 up of their habitat. The length of the life cycle is about the 



