REVISION MALACOSOMA HUBNER IN NORTH AMERICA 41 



for a black spot surrounding setal group SD. This is more precise 

 than merely saying that the lateral area is blue with a black spot. 



Secondary setae are very numerous and usually superficially obscure 

 most of the primary setae except the Dl group, even though the 

 primary setae may be differently colored. Quite often the secondary 

 setae will be one color on one part of the body and a different color on 

 another part. If they are different colors, those setae above the subdorsal 

 line (fig. 7) will be one color (almost invariably some shade of orange), 

 and those below the subdorsal line (fig. 7) will be another color 

 (usually a shade of white, but sometimes orange). Therefore, all 

 secondary setae ventral to the subdorsal line are called "lateral 

 setae," and all secondary setae dorsal to the subdorsal line are called 

 "dorsal setae." See figure 7. There are relatively few secondary setae 

 on the subdorsal area, so these dorsal and lateral groups of secondary 

 setae are quite well defined and easily observed. Many of the older 

 descriptions of Malacosoma larvae which refer to "dorsal" or "lateral" 

 setae undoubtedly are referring to the setae which occur on these areas. 



Color Pattern 



As has already been noted, the color pattern is quite useful in 

 distinguishing some species. The color pattern is most stable in those 

 species which are most easily separated by other means. Possibly this 

 results from the fact that these species {americamim, disstria, constrictum, 

 and tigris) are completely isolated and probably have been for a long 

 time in the past, while the other two species (californicum and incurvum) 

 are species which have reached a stage in evolution where some 

 populations are on the border between good species and subspecies, 

 resulting in highly variable populations between the more homogene- 

 ous ones. 



It is now known that the color pattern of californicum and incurvum 

 is highly variable, but in the past it was believed to be more constant. 

 Because it was believed to be more constant, it and setal color have 

 been used almost exclusively to distinguish between the "species" of 

 Malacosoma found in western North America ever since they were 

 described originally. For example, the color of setae is often mentioned 

 in larval descriptions, and in the case of ambisimile, one of the most 

 important ways of distinguishing ambisimile from californicum was the 

 color of the lateral setae (ambisimile had white lateral setae and cali- 

 fornicum had orange lateral setae). Extensive collecting of Malacosoma 

 larvae, however, has revealed that the color of the lateral setae is not 

 constant for any species. It varies from white to orange in all species 



