ITS INCREASE RETARDED. 5 



first extensive outbreak of the moth in Medford, and thus 

 became acquainted with its voracity and reproductive pow- 

 ers, were unable to understand how so destructive a creat- 

 ure could have existed unnoticed for twenty years. But 

 the moth was not unnoticed after the first ten years, al- 

 though its identity remained unknown and its spreading 

 attracted no attention outside the locality where it was first 

 introduced. Within twelve years from the time of its 

 introduction it had become a serious nuisance to those 

 living in and near the Trouvelot house ; but they then sup- 

 posed the caterpillar to be a native. Its lack of conspicuous 

 markings, which to the common eye would distinguish it 

 from other species, and its habits of concealment and night- 

 feeding will explain its unheeded distribution. Within 

 twenty years it had spread into thirty townships and gained 

 a foothold in each without attracting public attention. Of 

 these facts we have the most convincing proofs. 



INFLUENCES THAT AT FIRST RETARDED ITS INCREASE. 



A study of the growth of many isolated moth colonies 

 which have been found existing under conditions similar to 

 those influencing the Trouvelot colony, gives abundant proof 

 that the growth of such swarms for the first few years is ex- 

 ceedingly slow. 



The experiments made have not yet shown conclusively 

 how much the enforced and continuous inbreeding which re- 

 sults from isolation affects the vitality of the species. Field 

 observations show that in some cases isolated colonies have 

 come very near extinction in the first years of their exist- 

 ence, while others have died out. During the eight or ten 

 years following its introduction, the moth, while becoming 

 acclimated, battled against the many influences which served 

 at first to hold it in check. A consideration of the oper- 

 ation of these influences will go far toward explaining its 

 apparently slow increase during the first few years. It must 

 be considered that the nev/ -comer had much to contend 

 against. It had to encounter : 



1. A new and changeable climate. How potent were cli- 

 matic influences in controlling the increase of the species? 

 Such influences may have been felt for years. If the moth 



