INTRODUCTION. IX 



the quantity of food etc., which has gone to the production of the 

 wings and external structures in the male has been utilised in the 

 development of an excessive reproductive system in the female, and 

 it is also noticeable that most, if not all, apterous and semiapterous 

 females are capable of producing a large number of ova. In relation 

 to this matter of size Dr. Chapman has pointed out that Orgyia antiqua 

 female larvae have one more moult than the male Iarva3. 



It is a recognised fact that all animals have some means of escape 

 from their enemies, and that the female requires such special means 

 more than the male. It is also noticeable that many of the apterous 

 and semiapterous species occur in the winter or early spring when the 

 trees are bare and when the males become exceptionally conspicuous. 

 The females also of such as occur in the winter or early spring, move 

 about rapidly from place to place and hide in nooks and crannies into 

 which the male with his wings could not possibly enter. On the 

 other hand, the females of Orgyia, Psyche etc., emerge in the summer, 

 are scarcely able to crawl at all, have scarcely any means of locomotion, 

 do not hide in crannies etc., but lay their eggs and practically die in 

 the spot where they emerge. Here then are two distinct groups which 

 require separate consideration. They, however, resemble each other in 

 having similar means of planting their young in the world. They 

 produce many ova. Those that emerge in the spring or winter lay 

 their eggs in the crannies of the bark, twigs etc., at a time of the year 

 when they are much exposed and have to leave them largely to fate. 

 The great number of eggs they lay is their only chance in the struggle 

 for existence and they accordingly lay them. But herein the two 

 groups differ. The females of Nyssia, Hybernia, Anisopteryx, Exapate, 

 etc., search for these crannies to lay their eggs ; but a suitable egg- 

 laying place for the female has to be found by the larva in Orgyia, 

 still more being left to chance in Psyche where the supply of ova, 

 however, is practically unlimited owing to the parthenogenetic re- 

 production which takes place in this group. 



Let us look now at a few details in certain species which can be 

 taken as characteristic of the rest. Orgyia antiqua flies rapidly in the 

 sunshine at a time when insect-eating birds are most abundant, his 

 rapid flight undoubtedly aiding him in protecting himself. The 

 female with her large body cannot possibly be protected in this way. 

 To fly with the rapidity of the male she would require an immens9 

 wing area owing to the weight of her body. She, therefore, has to 

 hide, and the hiding place is provided when she is in the larval stage. 

 Her wings are useless and would betray her. In her apterous con- 

 dition, seated on her pupal web after emergence she looks so exactly 

 like a spider that only practical entomologists recognise her ; she lays 

 her eggs in the web and never stirs. To carry the matter a step 

 further, the eggs hatch a few at the time throughout the season, so 

 that it is scarcely possible for a whole batch to fail as they might 

 sometimes do if they "all hatched together owing to climatic causes 

 &c. As an example of the " Winter Moths " let us take Anisopteryx 

 cescularia. The male of this species is wonderfully protected. With 

 its slender body appressed closely to a twig, and its wings folded care- 

 fully round it, it is almost impossible to detect him. The female with 

 its large body would become very conspicuous in a similar position. 



