363 



CORRESPONDENCE. 



SCENT GLANDS IN LEPIDOPTERA. 

 I\Ir. Taylor's article in The Naturalist for October is exceedingly interesting 

 in a number of ways, the most important being that proof is given that 

 scent glands do exist in lepidoptera. It is welcome also because it gives 

 an opportunity of trying to clear the issue if possible, and also because Mr. 

 Taylor definitely claims conclusive proof that scent is a sexual necessity. 



Fully realizing the life-long experiences and keen powers of observation 

 of both my antagonists, I still contend that Mr. Taylor's ' probabilities ' 

 and Mr. Porritt's ' practical certainties' are not conclusive, for the issue 

 cannot be in anything short of the positive. 



I have not read Dr. Dixey's discoveries for certain reasons, and the 

 same reasons confine my principle observations to a restricted area in 

 the South West Riding, therefore it is hoped the following will not be 

 regarded as pedantic. The importance of the antennae cannot be doubted, 

 for it almost invariably happens that their preservation is perfect when 

 otherwise the insect is a perfect wreck, and one's experience is that if 

 they be removed from the male, or if the pectinations are filled with oil, 

 pairing will not take place. 



It is obvious that apterous females are a stumbling block to the vibra- 

 tion theory, and they would seem to prove that the vibrations oi winged 

 females are superfluous, but superfluities seldom occur in nature.* 



It would be folly to deny the existence of subtle scents below the 

 human sense, but principles on which convictions are based should not 

 allow anyone to attach importance to them until their presence is estab- 

 lished. But that odours are given off by some species is not in doubt, 

 for is there not a certain drawer which one occasionally looks into, that 

 contains a pupa case of a goat moth which for upwards of ten years has 

 been giving off a most objectionable ' stink ' that seemingly never dim- 

 inishes, but which in all likelihood belongs to intransitary things. One 

 accepted use for these odours is protection, but when it is definitely stated 

 that nasty ones have that use only, and that the more pleasing ones are 

 used for sexual purposes, a distinction is drawn which I admit is outside 

 my powers of conception ; for never has one had the least suspicion 

 but that everyone of them was for protection only. 



In the case of butterflies, their development has reached a high pitch 

 of perfection, hence their safety from bird attacks. 



A little more detail would be interesting as to whether the glandular 

 scent scales are permanently attached to the wings of butterflies, or on 

 the other hand, are freely shed like the ordinary scales during the activities 

 of the insects, in other words, are worn specimens scentless, for it fre- 

 quently happens when one finds butterflies paired the male is in a worn 

 condition. The cause of this is, that generally speaking in a butterfly 

 emergence, the males come out four or five days before the females, and it 

 would appear that they have a scent protection. It is perfectly imma- 

 terial whether the odours are pleasing or abominable to the human sense, 

 providing they are eftective for the butterflies. 



The odours given off by the garden tiger moth can be made to vary. 

 When the insect is disturbed it assumes a rigid posture and from two 

 pores behind the head exudes a yellow coloured fluid. If the larva was 

 fed on dock the odour is not unpleasant and suggests the smell of drying 

 oil paint ; but if the larva was fed on elder the odour has a most unpleasant 

 and powerful elder smell ; both sexes being' similarly affected. When a 

 virgin female is calling, that is, vibrating her wings, she does not polute 

 the air with her concentrated elder ' gas ' so far as one has noticed. Is 

 the musk scent of the convolvulus hawk moth given off by both sexes ? 



* Several papers on the causes of, and necessity for, apterous females, 

 appeared in the volumes of the Ent. Mo. Mag. for 1912 and 1913. — G.T.P.. 



1918 Nov. 1. 



