THE GIPSY-MOTH OF MASSACHUSETTS 241 



if trees and shrubs with green foliage are close at hand. The 

 spread of the pest to towns, villages, and farms miles away from 

 the original centre of infection was therefore hard to explain 

 until the circumstances were closely studied. It was then 

 remarked that towns were more affected than villages, villages 

 more than isolated farms, and farms more than agricultural 

 land without houses. The moths spread by preference along 

 main roads to populous places, which soon became new centres 

 of infection. In the end it was discovered that the chief means 

 of transport were the vehicles driven along the roads. Cater- 

 pillars dangling by threads were knocked off the trees, carried 

 along by the waggon or carriage, and set down in a place where 

 they had a fair chance of finding food and shelter. Any regular 

 communication by road between an infected and a non-infected 

 site was sure before long to serve as a means of transporting 

 the caterpillars. Nor were vehicles essential. People carried 

 the caterpillars a,bout on their clothes, and thus unconsciously 

 brought them into favourite places of resort, such as the 

 grounds enclosing public monuments. In the Mount Auburn 

 cemetery at Cambridge the trees around the graves of the 

 national poets, Lowell and Longfellow, were so regularly sup- 

 plied with fresh caterpillars that they had to be specially 

 watched and cleared. 



The methods adopted by the Massachusetts field-force have 

 been fully set forth in the report by Forbush and Fernald 

 . already quoted. The chief means of extermination were 

 these : — 



I. Destruction of the egg- clusters. — The most effectual 

 method of destruction is heat (a temperature of not less than 

 140 degs. F. or 60 degs. C. is required). The clusters may 

 be collected in tin cans and put into a fire. If heated in an 

 open vessel the clusters explode, and some eggs may be scat- 

 tered without being harmed. In other cases a flame was 

 directed upon the clusters in situ. Owing to the low con- 

 ductivity of a mass of eggs and hair, a passing flame is not 

 effectual. Petroleum discharged continuously from a is-gallon 

 tank in the form of ignited sprg,y was found to answer well. 

 Creosote and tar in various mixtures are tolerably effective 

 cold applications. In the search for egg-clusters iield-glasses 

 and pocket-mirrors were of use, the mirrors being employed to 

 examine the under surface 'of a rail near the ground, or other 



