180 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



spot around setal group Dl, but they usually have more conspicuous 

 orange markings, and a less prominent bluish to blue-white middorsal 

 stripe which is often about the same color as the subdorsal area. 



Possibly the best way to separate i. discolor atum larvae from c. fragile 

 larvae in the southwestern Utah area is by the color of setae SDl and 

 SD2. They are usually black on c. fragile and white on i. discolor atum. 

 This difference, however, cannot be relied on as a general character 

 for separating all i. discoloratum from all populations of M. californicum, 

 since setal color may vary within or between populations found in 

 different areas. For example, this same difference holds for populations 

 of californicum and i. discoloratum found at Buckhorn Wash, Emery 

 County, but at the base of the La Sal Mountains in San Juan County, 

 specimens of californicum collected on Cercocarpus montanus had white SD 

 setae instead of black. Only two tents were found, and no egg masses 

 were located, but the spumaline of reared females contained specks, 

 and confirms the identification of the C. montanus population as M. 

 californicum. Also, the adults which were reared from the C. montanus 

 are typical of californicum found in that part of Utah. The adults reared 

 from the Cottonwood are typical /. discoloratum, and the spumaline did 

 not contain any specks. Therefore, the white SD setae on the C. montanus 

 population is just another example of the great variation in characters 

 that is found throughout the range of A/, californicum. See the introduc- 

 tory section on "The Western Tenth uilders" (page 118) for a more 

 complete discussion of the differences between M. incurvum discoloratum 

 and M. californicum and M. calif ornicum fragile. 



EGG MASSES. — The eggs are laid as a flat clasping mass, covered 

 with a relatively tough spumaline which contains many small, fairly 

 uniformly sized bubbles. The spumaline is very light colored, being 

 white or nearly so as in figure 1 1 7, and without specks. Egg masses of 

 c. fragile are covered with a gray or gray-brown spumaline which has 

 many small specks, and egg masses of other populations of M. 

 californicum are covered with gray-brown or brownish spumaline which 

 may contain specks. See the introductory section on c^^ masses for a 

 discussion of the specks (page 20). 



TENTS. — ^Tents are large and essentially the same as those built by 

 M. californicum and M. americanum, and cannot be distinguished from 

 them. At several places along the Virgin River in Utah penultimate 

 instar larvae were observed clustering on large branches and trunks of 

 Cottonwood trees in a fashion similar to M. disstria. All of these trees, 

 however, had been almost completely stripped of their foliage, and the 

 larvae probably were in the process of abandoning the trees in their 

 search for additional food. 



