65 



west ; " " 22nd to 23rd, the same ; " " 27th to 28th, numerous 

 flights passing on." 



Fiddra Lighthouse, on an island off east coast of Scotland. 

 " 1886, August. Moths everywhere after darkness set in, 

 some very large and beautiful, and so numerous that they had 

 to be swept down with a towel." 



Would Light-vessel, ten miles off Happisburgh, on the 

 Norfolk coast. " 1884, June 7th, 4 p.m. Wind S.S.E, One 

 Death's-head moth caught alive, several small white moths 

 rested." 



However incomplete these reports may be, they appear to 

 prove most conclusively that moths do move to long distances 

 and in considerable numbers. Some of the lights, it is true, 

 are sufficiently near to the shore to admit of the probability 

 of the moths frequenting their lanterns, having been attracted 

 thither from the adjacent land ; but the very distinct reports 

 from Heligoland admit of no such interpretation, the 

 *' numerous flights passing on " clearly indicate masses in 

 a migratory condition, and the westerly course that they 

 were taking would bring them directly to these islands ; and 

 if so weak-winged an insect as Deiopeia pulchella could reach 

 the middle of the Atlantic Ocean, the 300 miles intervening 

 between Heligoland and the British Islands would form no 

 obstacle to a safe arrival of its hardier brethren on these 

 coasts; nor can we suppose that the narrow limits of the 

 English Channel would form a barrier to immigration from 

 the countries to the south of us. 



But other causes have been suggested to account for the 

 cases of abnormal abundance that we are investigating. The 

 insular position of our islands possibly engenders insular 

 prejudices in the minds of many of their inhabitants, and this 

 has perhaps led to many of the theories that have from time 

 to time been advanced without any sufficient evidence to 

 support them ; nevertheless, many suggestions have been 

 made that are worthy of the most careful investigation. 

 This is particularly apparent when we recognize the great 

 fecundity of many species, and yet the comparatively small 

 percentage that ever reach maturity. A $ Dicranura vinula, 

 L., has been found to contain 268 eggs ; Smerinthus ocellatus, 

 L., nearly 400. I have counted a similar number deposited 

 by Nyssia hispidaria, Fb., and Biston hirtaria, Clerck., is 

 known to be even more prolific ; yet we do not find an 

 annual corresponding increase in the number of imagines of 

 these species, their natural enemies hold them in check, and 

 maintain a balance of power. If, therefore, we are to account 



