118 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



(Holt Co.); Lincoln. Oklahoma: Hinton. south Dakota: Volga; "S. Dak." 

 TEXAS: College Station; Eastland Co.; "Texas." 



Canada. — Manitoba: Bernie Lake; 10 mi. E. Braintree; Charles Wood; 

 Garson; Gull Lake; Sandilands Forest Reserve; Stead; Tuelon; Winnipeg; 

 Winnipeg Beach, nova sgotia: Digby; Truro. Ontario: Asheribos Island, 

 Georgian Bay; Bracebridge; Britannia; Brockville; Bruce Mines; Constance 

 Bay; Dunnville; Grand Bend; Hamilton; Iron Bridge; Kemptville; Manitoulin 

 Island (Lake Huron); Mer Bleue; Merivale; Muskoka, Lake Joseph; North 

 Bay; Ontonque Lake; Ottawa; Paris; Parry Sound; Simcoe; Sprucedale; 

 Sudbury; Toronto; Trenton; "N. Ontario." Quebec: Beachgrove; Kazubezua; 

 Kingsmere; Kirks Ferry; Knowlton; Lac Mondor, Ste. Flore; Meach Lake; 

 Norway Bay. 



The Western Tentbuilders — A Comparison of 



Malacosoma californicum and Malacosoma incurvum in 



the Southwestern United States 



Specimens of all life stages of M. disstria, M. constridum, M. tigris, 

 and M. americanum can be positively identified by the diagnostic char- 

 acters listed for each species. Any remaining specimens will be M. 

 californicum or M. incurvum and their subspecies. Correct identification 

 of these two species and their subspecies is often diflficult and sometimes 

 impossible, but with good data and as many life stages as possible it 

 becomes much easier. 



Malacosoma californicum and M. incurvum are very closely related 

 species which cannot be absolutely separated from each other in every 

 case by any known characters of any life stage. Nevertheless, there are 

 some differences between them in the areas where they are known to 

 occur together which permit most specimens to be correctly identified. 

 They appear to present a very good example of the phenomenon of 

 character displacement as proposed by Brown and Wilson (1956). 

 They are not recognized as distinct species because of these diflferences 

 alone, however, since field observations made on them in Arizona 

 and Utah indicate that reproductive isolation is well developed, al- 

 though probably not 100 percent effective. It remains to be seen whether 

 or not these differences will be found in other parts of the Southwest, 

 and what will be found in the large and totally unstudied area stretch- 

 ing from southern Arizona to Mexico City. Still, the observed differences 

 should be recognized in some way, and regarding them as distinct 

 species seems to be the best way at the present time. 



Malacosoma californicum and M. incurvum were found in the same 

 vicinity only at several places in Utah. These localities were along 

 the Virgin and Santa Clara Rivers in Washington County, at Buckhorn 

 Wash near the San Rafael River in Emery County, at the foot of the 



