ON WiNGLESSNESS IS WINTEK MOTtlS. 45 



The force of a winter appearance in producing apterousness of the 

 female is further seen when we note that the tifteen species belong to 

 at least five, possibly six, difterent groups, by which the apterousness 

 niust have been separately achieved, e.;/., we have the Hibernias and 

 Nyssias (possibly one), Anisojitery.r, L'heiinatohia, ('lni)taharhc, and 

 Kxapate — three or four groups of Geoinetrids and two of micros. 

 The only commonly received explanation of the apterousness of 

 these moths is that the females, if provided with wings, would be very 

 conspicuous on the bare twigs, and would fall a prey too readily to 

 their enemies. They certainly do take advantage of their apterous- 

 ness to hide away very successfully, but are they more successful than, 

 say, the male of ('. bniniata, which is practically undiscoverable 

 by day, even when it swarms. 



I think there is little doubt that if wings were otherwise advanta- 

 geous — i.e., not definitely disadvantageous — the question of hiding 

 would have been easily solved m some other way. For purposes of 

 concealment and protection the wings of insects have undergone their 

 most numerous and important modifications, in texture, size, shape, 

 folding, markings, colour, etc., etc. The one, and, I fancy, the only, 

 reason for getting rid of wings is not that they present difficulties and 

 dangers, but that flight itself is definitely injurious. If flight is an 

 advantage, any difficulties connected with the wings are of secondary, 

 not primary, importance, and the wings are retained, but modified to 

 meet them. To explain any case of apterousness, then, we must find 

 some reason why Hight is injurious. iVny other dangers attaching to 

 the wings may, in a minor degree, be an assistance in losing them, 

 but by itself would not be an effective force. 



The one thing the moth has to achieve is to lay her eggs in a satis- 

 factory situation. In the Orgyias, Psychids, etc., wings were an evil, 

 because they would take the moth away from the best place for laying 

 her eggs. This is precisely the reason that has forced the " winter " 

 moths to lay aside theirs. 



These " winter " moths all belong to groups whose females lay their 

 eggs on the foodplant, somewhere or other, and there is no doubt, in 

 ordinary circumstances, such moths find the foodplant by scent. 

 During the growing season all plants, doubtless, throw off an odour 

 abundantly sufficient for this purpose. The moth flies from plant to 

 plant to lay her eggs, finding her way — usually in the dark — by scent. 

 But, how is it in the winter, when vegetation is dormant ? Plants 

 even then, probably, give off some scent, but it is, no doubt, so faint 

 that a moth on the wing with the ordinary powers of one of our 

 summer moths, would utterly fail to detect it. A moth that takes 

 wing in the winter will then have great, pi'obably insuperable, diffi- 

 culty in again finding the foodplant on which to lay her eggs. 



Our true " winter " moths got over it by losing their wmgs, and so 

 avoidmg the probability of going right away from the foodplant. But 

 how is the moth to find the foodplant on foot '? It emerges from the 

 earth, and may tramp away anywhere. In the first place, however, 

 it does do it, we know it does it, and does it easily and abundantly. 

 Probably pupation takes place where this shall be tolerably easy, where 

 the ordinary upward climb a moth does on emerging shall bring it to 

 the stem of the required tree. Possibly at these close quarters scent is 

 not altogether inappreciable. A large proportion then of the moths reach 



