FLIES OF THE GENUS OGCODES — SCHLINGER 303 



narrow creek, which is unevenly bordered by several types of meadow 

 grass, wild flowers, and a species of Iris. The grassy area is rather 

 narrow, usually not more than 25 feet from the water to the higher 

 ground. At the junction of the grass area and the higher ground, 

 large patches of sagebrush, Artemisia species, is located. It was in 

 this grassy area that the preponderance of spiders was observed, and 

 it was on the dead twigs of the Artemisia that J. W. MacSwain and 

 A. T. McClay first collected their specimens on June 28, 1951. On 

 July 12, 1951, I made a special trip to this location to check the 

 remarkable account given by the primary collectors. The trip 

 resulted in the following observations. 



The black parasite eggs were so thick on the dead outer twigs that 

 they were easily noticed at a distance of 20 or more feet. Upon closer 

 examination, large numbers of adult female flies, sometimes as many as 

 20 to 30 per twig, could be seen slowly walking up or down the twig 

 laying about one egg every 3 to 4 seconds in a very rhythmic fashion. 

 Some of the twigs were test-counted, and it was estimated that they 

 contained from 15,000 to 20,000 eggs per linear foot. Occasionally a 

 male landed on a twig, but most of the males observed and collected 

 were found flying among, or resting upon, the inner branches of the 

 sagebrush. Since most of the specimens of adaptatus were collected 

 by actually picking them from the dead twigs by hand, the absence of 

 males and the preponderance of females is self-explanatory. It was 

 noted, also, that about one-tenth of the available dead twigs contained 

 large masses of eggs and/or adult flies. The dead twigs themselves 

 were uncommon, and in no case were these twigs observed with only 

 a few eggs. 



Considering this last statement, it would seem that some sort of 

 association mechanism was acting on the adult females; otherwise, 

 some twigs would have been found with either a few eggs, a few adults 

 or a few of both. Whether this is a sight or smefl relationship I am 

 not sure, but the rapid rate of egg laying, together with the large 

 number of adults found per twig, indicated a "follow-the-leader" 

 condition in which somehow the females were attracted to the site 

 where the first female began her egg deposition. I observed this 

 condition also at Bolinas, Calif., on Juncus patiens E. Meyer, and at 

 Washoe Lake, Nev., on Chrysothamnus species. Kessel's observations 

 (1948) would also suggest this condition. 



A few topotype females were also observed laying eggs on the dead 

 flower stalks of an Iris species which was adjacent to the sagebrush. 

 These stalks also bore large masses of eggs. 



The first-instar larvae were seen "crawling" or "standing" on the 

 egg masses in typical Ogcodes fashion (see main biology section), so 



