44 



winter moth of Europe ; their external appearance and 

 habits correspond, and the difference in the season of 

 their occurrence in the perfect state may be occasioned 

 only by difference of cHmate. The canker-worm is 

 very irregular in its visitations. For a long period our 

 orchards may be entirely exempt from attack, and 

 then, during several successive years, immense num- 

 bers will appear, overspread fruit and forest trees, and 

 deprive them of their leaves at midsummer, when the 

 loss is most serious in its consequences. It is stated,* 

 that whole forests have perished, when thus stripped 

 of their sheltering foliage. Almost all insects, in the 

 perfect state, are furnished with wings : this insect is 

 an exception ; for, as you well know, the female is 

 without them ; a deprivation that fortunately confines 

 the individual within a hmited space, and renders the 

 migrations of the species slow and precarious. It was 

 for a while supposed, that these insects rose from the 

 earth only in the spring ; but it is ascertained that many 

 of them do also appear in the autumn or early part of 

 winter. In this vicinity f more were seen during the 

 month of October, 1831, than in the ensuing spring. 

 Irregularities in the period of the last developement of 

 insects are not unfrequent, and they are evidently 

 designed to secure the species from extinction. Com- 

 plete exemption from the ravages of the canker-worm 

 will depend upon keeping the wingless females from 

 ascending the body of the tree to deposit their eggs. 

 Many expedients to this end have, at various times, 



* Kalm. Travels, Vol. II. page 7. 



f I noticed their occurrence in the autumn in Cambridge, where, in 

 the open winter of 1830-31, an intelligent friend observed them 

 ascending in every month. 



