139 



NOTES AND OBSERVATIONS. 



The Probable Cause of the Decadence of British Butterflies. — 

 In the interesting discussion on this subject (ante, pp. 55, 102, 104). 

 LyccEiia arion is referred to as one of the species now on the point of 

 extinction. I have spent several years among the Cotswolds, and my 

 experience leads me to think that L. arion is often considered scarcer 

 than it really is. Not that I know of any spot where it is abundant, 

 but it turns up singly or in small batches in various localities. I have 

 spent hours wandering over the spot where it was so abundant twenty- 

 seven years ago ; but though L. icanis, L. adonis, L. an/iolus, and 

 L. minima are all found there, I have not seen arion within three miles 

 of its former haunt, nor have I heard of its capture in that locality. 

 Only last year I learnt that several — I think twenty-seven was the 

 number — had been taken, while several others were seen, on a steep 

 hillside, along which I have passed about twenty times in a season 

 without seeing any, so capricious is it in its choice of localities, I 

 know of eight localities where it has been taken in the last five years, 

 but would not set out with any confidence of finding it in any of them 

 in the coming season. Only a small proportion of the captures each 

 year get reported in the magazines, the majority being kept "dark," 

 as the captors are not subscribers to the ' Entomologist,' &c. 



Mr. Harcourt-Bath considers the isolation from the Continent as 

 the primary cause in the extinction of species. Isolation is a necessary 

 factor in the production of variations from the type, and Mr. Harcourt- 

 Bath believes in local variation. If there is this variation in the 

 different localities, then there must be isolation and inbreeding, for 

 the introduction of new blood would preserve the type and lessen the 

 amount of variability. If inbreeding is as injurious as Mr. Harcourt- 

 Bath assumes, then those isolated continental local varieties must be 

 dying out too, for many of the mountain forms are more widely sepa- 

 rated from their fellows of the same species than are our English 

 forms from those of the Continent. 



I cannot agree with Mr. G. H. Conquest " that agriculture is 

 practically the sole cause of the now comparative rarity of L. arion," 

 for there are many slopes to all appearances exactly suited to its 

 requirements — abundance of Thymus serpyllum, and not over-grazed — 

 where 1 have searched in vain for both the larvae and the imago. 

 Burning the herbage may destroy some larvfe, but it cannot extermi- 

 nate a species like arion. 



The abundance or scarcity of a species is due to climatal causes, 

 most insects being extremely sensitive, especially in the early larval 

 stages, to changes of heat and cold, drought and moisture, the larvae 

 perishing very often from no apparent cause. The conditions most 

 favourable to each species are necessary to enable a small percentage 

 to reach maturity, and then these conditions cannot suit each species 

 alike. Similar instances occur in botany, plants being most extraor- 

 dinarily abundant some years and scarce in the intervening periods, 

 for which we are unable to find a satisfactory solution. Perhaps the 

 instance that most readily occurs to me is the extraordinary abundance 

 of Ophrys apifera in 1885 on the Cotswolds, while it has been scarce 

 ever since in those spots where one could not walk without treading on 



