434 HOUSEHOLD INSECTS 



for the fine hairs are blown everywhere by the wind. 



Clothing hung out of doors near the larvae becomes 



covered with the hairs which may nettle the whole body 



when the garments are worn. 



Moreover, the cocoons of the insect contain nettling 



hairs derived from the caterpillars and are dangerous to 

 handle. Finally, nettling hairs become 

 scattered over the bodies of the moths, 

 and are found among the long hairs 

 in the tuft on the end of the abdomen. 

 Unquestionably, " brown-tail rash " 

 or dermatitis is the severest disease 

 caused by nettling caterpillars in this 

 country. For many years, it was held 

 that the disease was caused merely by 

 the mechanical irritation produced by 

 the hairs when in contact with the skin. 

 This, however, has been disproved and 

 the real cause shown by Tyzzer of 

 Harvard University. 



The nettling hairs of the caterpillars 

 are short, straight, tapering, needle- 

 pointed shafts, barbed for their entire 



FIG. 150. Poisonous , ,, ,-,-,. -,<-r\\ rr\\_ i , i 



hairs (P) and ordi- length (Fig. 150). These short, brown, 

 nary hairs (fi) of the nettling hairs are found on the tuber- 



brown-tail moth , , , , j -j e , i T_J 



caterpillars. c l es on the back and sides of the abdo- 



men. They seem to be hollow and 

 filled with a fine granular material that evidently con- 

 tains the urticating properties. The evidence indicates 

 that the poisonous material passes out of the hair at the 

 basal point, although Tyzzer was never able to demon- 

 strate the presence of an actual opening at this end of 



