FOURTH WINTER MEETING.— DECEMBER 8th, 1903. 



'THE COLOURS OF INSECTS."— By A. U. BATTLEY, Esq. 



A well-attended meeting' was held in the 

 Reference Library of the Beaney Institute on 

 Tuesday, December 8, 1903, S. Harvey, Esq., F.l C, 

 F.C.S . in ihe chair. After Miss Sworn had kindly 

 read the report of our delegate to the British 

 Association, the President introduced the lecturer, 



Mr. 4. U. Battley, who said : — My subject 

 to-night har. been announced as 'The Colours of 

 Insects," but the examples I shall select are 

 nearly all taken from the well-known group of 

 " Lepidoptera " (Butterflies and Moths), which 

 have been for many years my favourite study. 

 The colours of these, whether in the perfect, 

 larval, or even egg state, are always worthy of 

 admiration, the grouping, blending, or contrast 

 being perfect, as in most natural objects, and form 

 a lesson to artists and others which they would do 

 well to &tudy. Indeed, it is a great pity that 

 while artists use models and studies for nearly all 

 the objects in theii pictures, they frequently mar 

 the whole by introducing a perfectly impossible 

 butterfly, or even the wings of a butterfly with 

 the bead of a motb. Surely the insect itself is 

 beautiful and perfect enough without any 

 improving. My purpose to-night, however, is not 

 so much to treat this subject from an artistic 

 standpoint, as to give some insight iuto how these 

 colours are formed, and for what purposes they 

 exist. I am afraid I cannot pretent anything 

 new, but my object will be to place before you a 

 subject that will interest lepidopterists and others 

 alike, as the main rules enunciated hold good in 

 all branches of Nature. 



The wiags of Lepidoptera are themselves trans- 

 parent and colourless, being similar to those of 

 the house fly, but have on their surface scales 

 which bear the colours. These are of two kinds : 



(1) Non-pigmeatal, caused by the breaking up 

 of a white ray of light on the surface of the scale, 

 similar to the colours observable inside oyster 

 shells. 



(2) Pigmental, caused by the white light being 

 absorbed by the scale, and part given off again. 

 This class of colour is readily affected by exposure 

 to light, acids, alkalies, etc , which do not affect 

 the first class, an important matter to bear in 

 mind when arranging cases intended for constant 

 exposure to the light. 



The lowest development in colour occurs in the 

 female of Aporia cratxgi, where the scales towards 

 the centre of the fore wings are qnite transparent, 

 then comes the non-pigmental white, and this class 

 of colours is devel' ped in probably every shade. 

 In pigmental colours, the lowest form is white, 

 which develops into yellow, thence by one branch 

 through orange and red or brown to black, or by 

 another branch from yellow into green, thence 

 through red into blue or purple and possibly black. 

 There are also several casts of reversionary colours, 

 the yellow varieties of thr Burnet mtiths (f'oui the 

 typical red), Colias edusa (yellow) with its white 

 variety Helice, and the non-pigmental white in the 



male Hepialus h^imuli (from the yellow and 

 orange female), being some of the most notable. 

 In connection with these lines of colour develrp- 

 ment, it is interesting to note that botanists 

 have placed the development in flowers in almost 

 the same order. Colours in larvs can only be 

 treated briefly. The brown and brightly coloured, 

 also some of the green larva?, have a layer of pig- 

 ment under the skin, but the latter especially are 

 much influenced by the green blood, and there is 

 consequently great difticulty in preserving them 

 to show their natural colours. 



Colours, whether in the laiva or imago, can 

 generally be shown to be useful to the insect, 

 either now or during past ages, time not having 

 yet been sufficient to delete it. In fact the ex- 

 ceptions to this rule are so few and constantly 

 becoming fewer as our knowledge extends, that we 

 niay reasonably assume it is always the case. 



These colours must have been developed by 

 ages of natural selection. To properly appreciate 

 the effect of this in the case of Lepidoptera, it is 

 necessary to consider for a moment the enormous 

 struggle for existence constantly going on. A 

 female of Hoporina croceago taken by me last 

 spring laid 537 eggs in captivity,while I estimated 

 another batch of noctua eggs found on a reed at 

 about 1,250, but even assuming that these were 

 outside numbers, and putting the minimum at 

 200, it would only be necessary for two of these 

 to come to maturity and fulfil the purpose of their 

 existence in order to preserve the balance of the 

 species. That is to say ,99 per cent, perish normally, 

 either from climatic causes or by enemies. Now 

 a very small advantage would save one out ot this 

 ninety-nine, with the result that next year the 

 number of species would be doubled. 



Parallel variation may be regarded as a factor 

 in guiding colour formation, that is, if we 

 have two closely allied and normiilly distinct 

 species A and B, we shall find that a tendency 

 exists in A to vary in the direction of B, and in B 

 to vary towards A, this is possibly of a reversionary 

 nature. 



Sexual selection is also believed to have afi'ected 

 colours in some instances, owing to the preference 

 by the females for brightly coloured males, and 

 although this is not now regarded as so [owerlul 

 a factor as formerly, there are a few well known 

 examples. In the Ghost moth {Hepialus humuli), 

 the position of the sexes is reversed, the female 

 seeking the male, to whom she flies attracted by 

 his white colour as he buzzes over the herbage in 

 the dusk. J he root of this genus are brown with 

 a tew silvery markings, and it is only fair to 

 assume that the oricinal H. humuli male was so 

 coloured, the specimens with the most silver would 

 then be selected by the female, until a perfect 

 white male was the result. Further, in the 

 Shellands, where there is no dark during June 

 and July, this species has perforce to fly in the 

 daylight, and the necessity for the white male 



