REVISION MALACOSOMA HUBNER IN NORTH AMERICA 5 



color and pattern). Stretch (1881), the describer of several species of 

 Malacosoma, comments: "In studying the genus, we must depend 

 chiefly on the transformations for the separation of species, and where 

 these are unknown, not so much on color as on the structure and pro- 

 portion of the markings, as the species are very variable and approach 

 each other in the imagines." Henry Edwards (1882) in describing M. 

 incurvum says: "It is rather a hazardous experiment to describe a 

 species of this genus, without a knowledge of the preparatory 

 stages . . ." More recently, Langston (1957) makes the following 

 statement concerning the identification of Malacosoma: "Many species 

 of Malacosoma are so highly variable in the adult stage that it is almost 

 impossible to separate them taxonomically. The larvae are quite 

 distinct for most species, however, and are used as the basis for separa- 

 tion." 



The literature, however, contains a few statements which indicate 

 that the larvae are not as constant or as different as generally supposed. 

 Langston (1957) says the larvae are quite distinct for most species, 

 implying that some larvae may be difficult to identify. And Clark 

 (1956, 1958) in his studies on the ecology of polyhedrosis of tent 

 caterpillars has commented on variations in both larvae and adults 

 that he observed in California and New Mexico. Even in the older 

 literature, statements indicate that considerable variation was present 

 in the larvae. For example, Dyar (1893) in the original description of 

 M. pluviale says of the larva: "Body black, a pale blue dorsal line, 

 divided between the segments, obsolete at the extremities, and forming 

 9 rather narrow, elongate, blue spots, tapering at their ends, exactly 

 as in C. fragilis." (C. fragilis is the so-called Great Basin tent cater- 

 pillar.) Dyar (1895b) made the following additional remarks in com- 

 paring the larvae of pluviale with fragile: 



The fully marked larvae look strikingly different from fragilis, yet the 

 two are exactly alike in pattern, and whereas in pluvialis the orange 

 marks are greatly developed and the blue reduced, m fragilis the orange 

 is reduced almost to obliteration and the blue greatly extended. Mr. 

 Stretch has noted a considerable range of variation in the Astoria 

 larvae. He says that they varied by the expansion or contraction of 

 the dorsal orange markings, and in the latter case the blue became 

 strikingly visible. This is a greater range of variation than I have 

 happened to observe in any one locality, but the specimens sent me 

 by Mr. Piper have the orange considerably reduced. I suspect that as 

 we go East the orange marks will tend to be supplanted by the blue, 

 and this species will grade into fragilis. However, I have yet to see 

 larvae which are not definitely one or the other, and the moths seem 

 not to pass into each other, though the Idaho region is still to be 

 explored. 



