68 



Marlborough House were in many cases denuded of their 

 leaves, and others had large branches served in the same 

 way, some of the thorns in the parks were also attacked. The 

 moth had been very common at Lewisham in 1880, but was 

 not so in the previous year {Entoni. xiv. 178). 



From the foregoing, three things will be noted : firstly, 

 the districts affected are all of small area, and not of 

 general distribution throughout the country ; secondly, 

 the abundance occurred in the larval stage ; and thirdly, 

 that the species affected are almost without exception 

 those having apterous females. This last fact appears 

 to explain the first two, wingless moths could not be 

 expected to move to long distances, hence it is probable 

 that any abundance resulting from conditions controlling 

 them would be limited in area, and the first we should see 

 of it would be in the larval state ; it is true that at times the 

 moths also are unusually abundant, but so far as I have been 

 able to ascertain these cases of abundance of larvje have not 

 always been the immediate forerunners of a corresponding 

 abundance of imagines ; indeed, it appears that the reverse 

 would probably be the case, the rapacious appetites of the 

 multitudes of larvae often causing their destruction ; and in 

 addition to this I have noticed that with the abundance of 

 the larvae there has been a corresponding increase in their 

 parasitic enemies. This was very apparent in the case cited 

 from Chattenden, where ichneumons were literally in 

 thousands ; and many of the bright green larvs of Oporabia 

 dihitata taken from the denuded oak trees at West Wickham 

 had their conspicuous white ova attached to them. This 

 does not, however, account for the abundance, but rather for 

 its sudden check ; yet considering the question of these 

 wingless creatures as a whole, we might well ask whether, if 

 we can account for their sudden decrease by apparently local 

 detrimental influences, the reverse of such conditions would 

 not be a correct solution of an equally sudden increase in 

 their numbers ? But we have one piece of direct evidence 

 that must not be overlooked ; the report from Heligoland 

 lighthouse distinctly mentions large flights of H. defoliaria^ 

 etc. Need we then wonder that the vioth is sometimes 

 abnormally common here ; and although I do not for one 

 moment suggest the presence of any of the wingless females 

 in these advancing swarms, it is far from improbable that the 

 arrival of numbers of the opposite sex would materially 

 affect the status of the species here, and possibly become an 

 important factor in the occasional abundance of larv^ that 



