SCIENTIFIC NOTES. 127 



J^CIENTIFIC NOTES AND OBSERVATIONS. 



The preference of butterflies for sunlight. — I have been reading 

 in the Transactions of the Entoniulot/ical Societij of London the brilliant 

 and stimulating paper by Mr. Thayer, and the more cautious, if more 

 subtle, summing up by Professor Poulton, on "Protective Coloration 

 in its relation to Mimicry," etc. Although I have neither the scientific 

 nor artistic knowledge and experience that is necessary for its adequate 

 discussion, still, I feel as rashly compelled to offer a few remarks as I 

 did when, without any first-hand experience of the tropics or living 

 exotic Sphingids, I ventured to object to the use of such structural 

 details as the size and position of the eyes, length of tongue, cut of 

 wings, and shape of the abdomen, as generic characters, pointing out 

 that differences of environment, such as lack of twilight and the large 

 size of tropical flowers, together with the position of these latter above 

 instead of below the insect's plane of flight, etc., were quite sufficient 

 to account for, and in all probability had produced, the difference between 

 the European specimens of Hijles euphorbiae and its Indian relative 

 H. lat/ti/riis, Walk., in regard to which, even if authorities had joined 

 issue as to its right to rank as a species, none cared to press its claim 

 to generic rank. My rashness in the present instance will, however, 

 be seen to be even greater, when I confess that I have never been out 

 of Britain, and that my opportunities of observing butterflies, even 

 under our cool grey skies, have been all but a negligible quantity of late 

 years. But the fact that I have been present at entomological meetings 

 off and on for the past twelve years, and have never yet to my memory 

 heard the question asked or the point discussed, emboldens me to ask 

 the question, " Why do the Rhopalocera only fly when the sun shines? " 

 Here a doubt arises ; perhaps they do not do so abroad, and the few 

 English exceptions become the rule under tropical skies. In spite of 

 my expectations, I found to my surprise that Mr. Thayer did not 

 discuss the point, nor did Professor Poulton refer to it ; so, at the risk 

 of attempting to explain the obvious, I would suggest it is not alone 

 the need of greater heat, nor yet because their sight is defective that 

 they therefore require more light than the Heterocera. The bulk of 

 the last-named group are twilight or night flyers, and the exceptions to 

 this rule have for the most part either a rapid or buzzing flight, or are 

 species that feed whilst hovering, or closely fold their wings and settle ; 

 or if they have ample wings and fly at a moderate pace, they are 

 brightly if not brilliantly coloured. There is undoubtedly a connection 

 between brilliant coloration and vivid light, as Eimer pointed out, 

 although his explanation breaks down under the most cursory examina- 

 tion. Does this not greatly support Mr. Thayer's case "? After a perusal 

 of his paper, we see why it is necessary, or at any rate politic, for the 

 butterfly to settle and close its wings at the passing of every cloud. It 

 is not due to a whimsical distaste to dullness or fear of the slightest 

 chill, but to the danger it experiences in the absence of the brilliant 

 illumination that safeguards it by producing its effacement. according 

 to Mr, Thayer's theory. The marked disfavour with which most 

 butterflies seem to regard the afternoon sun. may also be partly due to 

 the difference in value of its lighting capacity as well as to the more 

 commonly given reasons of dry heat and insufficient moisture. That 

 the strength of the lighting is an important factor in the protective 



