132 THE ENTOMOLOaiST's RECORD. 



Why is Cyaiiiris semiargus no longer a British Insect? 



By T. A. CHAPMAN, M.D. 



There seems to be no evidence that Cyaniris seniianjKs still inhabits 

 the British Islands. The causes of its extinction do not appear to be 

 at all known, yet it seems very desirable that we should, if possible, 

 ascertain sometliing about it. Last summer (1908) 1 reared a few 

 larvae from the egg, and the survivors are now (October) entering into 

 hibernation. In noting their habits, I have been led to speculate as to 

 whether they help us to get nearer some theory as to the extirpation of 

 the species as a British insect, and I am tempted to state some of the 

 ideas that have occurred to me, in the hope that they may be criticized 

 so as to elucidate the subject a little further. 



I may say, briefly, that the butterflies would hardly lay on fjjta» 

 cornictdatiifi, which the larvte would, however, eat, but did so freely on 

 heads of red clover {Trifolimii praten>ie) on which the larvfe seemed so 

 much at home and with such straightforward procedure that I enter- 

 tain no doubt that it is its favourite food. It eats less readily white 

 clover {Trifoliiiiii repens) and could doubtless exist on other clovers and 

 less closely allied Le(/iiniinosae. I take it therefore as fairly certain that 

 red clover is the food-plant wherever it is available. The absence of 

 the food-plant cannot then be the cause of the decay of the species 

 with us. Yet, broadly speaking, I think agricultural reasons are at 

 the root of the matter as in the case of Chrysophanus dispar, but 

 certainly in some totally different manner. Climate can h^ve nothing 

 to do with it. C. si'inian/iifi does, no doubt, like a warmer summer than 

 is necessary, c.y., to Palyoiiiuuitus Icarus, but it is capable of standing any 

 amount of cold, occurring where the snow lies for several months. It 

 was once sufficientl}' widel}' distributed in the southern part of Great 

 Britain to show that it finds nothing inimical to it in our natural con- 

 ditions, still our earliest information about it suggests that they did not 

 fully meet its requirements. Some change, however, has occurred in 

 the last 50 or 100 years that slowly made it rarer and finally extinct. 

 The question of dates is no doubt important, and, unfortunately. I am 

 rather ignorant of the changes in agriculture during this period, and 

 especially of their exact dates. 



My general idea, however, is that the butterfly would be inevitably 

 attracted by clover-fields and would lay most of its eggs on cultivated 

 clover ; and, if for anj' reason eggs so laid never arrived at maturity, 

 only those on wild clover would remain to continue the species, and 

 these would very soon disappear by this migration of so large a propor- 

 tion to the cultivated fields. The species would be unaffected in 

 districts where wild clover was abundant and cultivated clover rare, 

 provided the wild clover was not severely grazed or cut for hay. The 

 larv* hatching in the flower-heads of the clover, just as flowering is 

 going over, feed up in a few weeks, till about a quarter of an inch long 

 and ready to hibernate. These larvae would perish if the clover was 

 cut before the larviv reached this stage — and also if the clover was 

 ploughed up during the winter, when the hibernating larv;e would 

 inevitably perish. 



Probably the mowing machine completed the extinction of the 

 species, by enabling the harvesting of the clover to be done more 

 rapidly and ensuring that the whole field was cut before the larva? had 



