32 



CIRCULAR 4 64, U. S. DEPARTMENT OF AGRICULTURE 



They never attack conifers and are seldom found on hickory, ash, or 

 other trees. 



Oak foliage is one of the favored foods of the brown-tail moth cat- 

 erpillars in Europe and was severely injured in New England for a 

 number of years after this insect became established there. It has not 

 suffered in this way in recent years except in Maine and New Hamp- 

 shire in 1933, when the insect was unusually abundant, and then some 

 webs were found on oak trees and the caterpillars caused considerable 

 defoliation locally. 



INJURY CAUSED BY THE BROWN-TAIL MOTH 



The principal injury caused by the brown-tail moth is due to the 

 feeding of the larvae in the spring. The caterpillars are often numer- 



FlGURE 17 



hibernating webs on the twigs. 



ous enough to devour the leaves as fast as the trees are able to develop 

 them. As the webs are made on the terminals, the growth of the 

 trees is often severely checked. In severe infestations trees may be 

 completely stripped (fig. 17), but as the larvae grow rapidly during 

 the first part of June there is usually an opportunity for the trees to 

 produce new leaves before midsummer. The larvae hatch in August 

 and frequently skeletonize the leaves, but this does not damage the 

 trees seriously, as the growing period for the season is nearly over. 



The bodies of the caterpillars are provided with poisonous hairs. 

 A microscopic examination of these hairs shows that the edges are 

 barbed in such a way as to cause intense irritation when they come in 

 contact with the human skin. They are also hollow and contain a 

 substance which acts on the blood corpuscles. Poisoning and irrita- 

 tion caused by this insect are accompanied by external swelling, and is 

 known as the brown-tail rash. Persons differ in their susceptibility 

 to this poison, but many cases are reported each year in the infested 

 Many camps and summer cottages cannot be occupied with 



area. 



