Moths 63 



were all in most unusual numbers ; while on other occasions 

 I found their places taken by Cheimatobia boreata, Odontopera 

 bidentata, Hybernia aurantiaria^ and Tephrosia crepuscularia, 

 besides many Selenia lunaria and Amphidasis betularia. Any 

 of these could have been collected by dozens, without 

 trouble, and there were many other species which were not 

 properly identified. Moths were also plentiful in some 

 places, chief and most attractive amongst them being the 

 pretty little Venilia macularia, the Rivulets, Emmelesia 

 albulata, and E. decolorata ; and Eubolia palumbaria. 

 Amongst the latter were many unusually small specimens, 

 but no other very striking varieties were noticed. 



There is still much uncertainty as to the causes which 

 lead up to such years of sudden increase in the insect world, 

 but whatever they may be, it was clear that in this case they 

 were not confined to merely one or two species. It was 

 also interesting to note within what narrow limits the 

 beneficial conditions had prevailed. In one dingle, or in 

 one copse, the caterpillars were in hordes, and the trees all 

 bared of leaves, while in the next there might be hardly a 

 trace of them. That similar cases of sporadic increase are 

 sometimes attributed to immigration (as for example with 

 the Diamond-back moth, Plutella cruciferarum\ I am well 

 aware ; but in this instance, at any rate, immigration was out 

 of the question, since the females of some of the most 

 abundant species are unable to fly, and therefore cannot 

 travel ; and it is not unreasonable to assume that the causes, 

 which operated so powerfully in favour of the increase of 

 one species, may also have had a like influence upon the 

 others. We therefore discard the immigration theory as 

 altogether inapplicable here, and must seek the true explana- 

 tion in other directions. The number of eggs laid by each 

 female moth, that reaches maturity, is no doubt subject to 

 some variation in different species, but is always considerable, 

 and we shall probably be well within the mark in putting it 

 at 300 in the case of most of those more particularly under 

 discussion. I once counted the eggs contained in the body 

 of another wingless species, the Vapourer, Qrgvia antiqua, 

 and found them to exceed 500. If, for the sake of 



