34 UNITED STATES NATIONAL MUSEimi BULLETIN 2 76 



It may be of interest from the medical point of view to note that 

 some people have an allergic reaction to the powder found on the co- 

 coons. The reaction results in a red welt appearing on the skin in areas 

 contacted by the powder. The welts somewhat resemble those caused 

 by nettles. The reaction is most severe where the skin is folded and 

 moistened by perspiration, such as on the neck and around the eyes. 

 Little or no reaction occurs when the skin is not moistened, so it may 

 be necessary for the powder to get into open pores before any irritation 

 takes place. 



The reaction is accompanied by rather intense itching, but can be 

 relieved by a good washing with soap and water. Apparently, this 

 removes the irritating material, but the welts do not disappear for 

 some time. This reaction has been observed on three persons who 

 have other allergies. One is allergic to ragweed pollen, the second to 

 ragweed and grass pollen, and the third to grass and tree pollen. No 

 reaction has been observed in persons who do not have some other 

 known pollen allergy. It is conceivable that, when Malacosoma popula- 

 tions are high, enough cocoons could be present in an area for the 

 powder to affect allergy-suffering persons working in such an area. 



Adults 



Adult Malacosoma are sexually dimorphic. In addition to genitalic 

 differences, normal males have smaller, differently proportioned wings, 

 smaller bodies, longer antennal rami, and sometimes they are colored 

 differently than females of the same species. These differences are 

 strikingly demonstrated by two bilateral gynandromorphs (figs. 204, 

 207) that were reared during this study. 



The M. americanum gynandromorph was reared from mature larvae 

 collected near Fredericksburg, Gillespie County, Texas. The M. 

 californicum californicum gynandromorph was reared from an cg^ mass 

 used as a control during Fj rearings. Both parents of this gynandro- 

 morph were reared from larvae collected at Belmont, San Mateo 

 County, California. It is interesting to note that one gynandromorph 

 is a left-side male, right-side female while the other one is the reverse. 

 The percentage of gynandromorphs in natural populations is quite 

 low, only 2 out of more than 9,000 reared adults in this study, but 

 Malacosoma gynandromorphs are not extremely rare since quite a few 

 have been reported in the European literature (see Collier, 1936, for 

 a list of references to some of them). 



If males and females are considered separately, adult Malacosoma 

 of all species are remarkably uniform in structure. Both males and 



