FLUCTUATION IN NUMBERS OF LEPIDOPTERA. 275 



It is beside the question, perhaps, but the fluctuation in abundance of 

 (Jh'siocaiiipa castrfU'^is appears to be on all fours with that of P. r-albuiii, 

 in the western counties of England, FAujonia polychlonn, LitJiosia 

 (h'lilana, (hntistis quadra, (jrunpliria nibricollis, Heterogenea cruciata 

 {asella), Lophopteri/xcannelita, Mniiia orion, Dicycla oo, Cidaria sagittata, 

 and numerous other undoubtedly sedentary species. These species 

 occasionally occur in large numbers for a season, and then, owing to 

 no reason that entomologists have yet been able to explain, have 

 become very rare for a number of years, only to reappear at some 

 future time in their old haunts in greater abundance than ever. 



There is no doubt that many entomologists in this country would 

 consider that this uncertainty in the appearance of these species is a 

 bona fide reason for their protection, and they would urge that no 

 outside factor should be allowed to increase the precarious position 

 that such species hold in this country. Such a reason is, in my 

 opinion, a good one for protecting such species as Aporia crataciji, 

 Ladia caenosa, a,nd perhaps Porthesia chrgsorrhoiM, should the two former 

 still exist in this country, but I am not sure whether the abundance of 

 any one of the "fluctuating" species, just enumerated, would be 

 influenced the year following an exceptional abundance, even if no 

 collecting of the species took place when it was abundant. 



Classifying the list published by the Protection Committee {ajite, 

 p. 214), it appears to me to divide up as follows'^ :^I. Species that 



HAVE BECOME PRACTICALLY EXTINCT FROM UNKNOWN CAUSES ApOVia 



cratae(/i, Porthesia cJiri/sorrhoea. II. Species that have become more 



OR LESS rare owing TO OVER-COLLECTING IN MOST OF THEIR KNOWN 



HABITATS — Melitaea cinxia, Lycaena arion, Xola albidalis, Cnaemido- 

 jdiorus rhododactylus. III. Species that have been much over- 

 collected IjOCALL.y — Melitaea athalia, Apatura iris, Papilio viaeliaon, 

 Carterocephalus palaemon, Scoria dealbata, Zygaena meliloti, Plusia 

 chrysnn. IV. Species that probably have been over-collected 

 locally — LeucopJiasia sinapis, Limenitis sibylia, Thecla pruni, Thy- 

 meliciis actaeon, Eulepia cribrum, Epione 'parallelaria, Fidonia limharia, 

 Cidaria reticxdata. V. Species concerning which there is no evidence 

 to prove that their abundance has been lessened by over-collecting 

 — TrocMlium scoliaeforme, Zygaena exulans, Kola centonalis, LitJiostege 

 griseata. VI. Species that are probably as abundant as ever, but 

 fluctuate in numbers from year to year — Nola strigula, Clisiocampa 

 castrensis, Mama orion, Acosmetia caliginosa, Dianthoecia irregularis. 

 VII. — Species that very few collectors know anything about, and 

 NOT LIKELY TO BE OVER-COLLECTED — Drepaua havpagida, Agrotera 

 netnoralis. It is quite possible that some of these species want pro- 

 tecting locally, especially those classified under III, and IV., but I 

 doubt whether all (or any) of these should be included in a list to be 

 applied to the whole of the British Islands. 



To show that the fluctuation in the abundance of Lepidoptera is 

 not confined to the British Islands, I should like to quote a few notes 

 made by Niceville as to certain tropical insects. In tropical forests, 

 one would expect to find the outside disturbance set up by man at a 



* I would apologise here for using up-to-date nomenclature. It appears 

 strange for such a go-ahead committee to be as far behind in its nomenclature, as 

 it appears to be in its knowledge of the distribution, etc., of some of the British 

 species. — J. B. 



