12 FARMERS' BULLETIN 845. 



to a considerable extent. This does not damage the trees seriously, 

 as the growing period for the season is nearly completed. 



The bodies of the caterpillars of the brown-tail moth are provided 

 with poisonous hairs. A microscopic examination of these hairs 

 shows that the edges are barbed in such a way that when they come 

 in contact with the human skin and are pressed into the flesh, intense 

 irritation is caused. These hairs are also hollow and contain a poi- 

 sonous substance which acts on the blood corpuscles. This causes 

 serious poisoning and severe irritation accompanied with external 

 swelling and is known as the brown-tail rash. Persons differ con- 

 siderably in their susceptibility to this poison, but many cases are 

 reported each year in the infested region, most of which are more 



FIG. 5. Apple trees stripped by brown-tail moth caterpillars. Note old winter webs at tops of trees. 



serious than those of ivy poisoning. Many camps and summer 

 cottages, particularly in wooded areas, can not be occupied with 

 any comfort during the early summer on account of the poisoning 

 resulting from these caterpillars. If clothing is hung on the line 

 near badly infested trees, the hairs frequently find lodgment and are 

 brought into the houses, and later severe poisoning may result. 



NATIVE ENEMIES. 



One of the most important natural enemies of the brown-tail moth 

 is a fungous disease, 1 which attacks the caterpillars, particularly in 

 the spring. It was first reported in this country by Dr. Roland 



1 Entomophthora auUcae. 



