66 BRITISH BUTTERFLIES. 



that the immovable position adopted by the larva of Ruralis betidae, as 

 well as its unfailing position of rest along the midrib of a leaf, combine 

 to form a most efficient meaDs of protection, the larva being, indeed, 

 most difficult to detect. 



We do not, however, believe that the larvae of the Satyrids, with their 

 longitudinal markings, especially when adult (or almost so), are to be con- 

 sidered as special (so much as general) cryptic forms, i.e., we think that 

 the larvae owe more to their general, than to their detailed, resemblance to 

 their surroundings, and that the longitudinal lines are more effective 

 as producing effects of light and shade, than an exact similarity to the 

 parallel venation of the grasses on which they rest, and this is the more 

 readily believed because of the dimorphic or dichromatic conditions 

 arising in many of the adult larvae as they approach maturity, so 

 many presenting two distinct shades — green and brown — of ground 

 colour marked with darker lines, the brown forms being probably as 

 strongly protective among the dying culms, as the green on the living 

 ones as summer advances. Poulton also argues that this larval 

 dichromatism is advantageous to the species, because, when once a 

 larva of one of the colour forms has been discovered by an enemy, 

 others of the same colour would be more easily found by this enemy, 

 whilst the other would be overlooked, so that, whilst one form might 

 suffer, the species would be saved through the escape of the other. 

 Weismann believes that this change has been brought about by natural 

 selection, but Semper urges that selection " could not possibly effect 

 any alteration in the pigment, but could only operate after such a 

 change had occurred," whilst Scudder rightly points out that such 

 changes may occur in nature directly, and instances the fact that, in a 

 number of caterpillars, and, particularly in those of the Papilionids, 

 an entire change of colour takes place just previous to pupation. Of this 

 particular change in colour he says (op. cit., p. 1146) : " The period of 

 pupation is probably the most hazardous for an insect, so far as its active 

 external foes are concerned, it being absolutely helpless at this period and 

 in a very sensitive state. The time required for the change is much 

 greater in any one species than for ordinary ecdysis in the same 

 species, and, whatever the purpose of the change in coloration may be, 

 it will hardly fail to be noticed that, in general, all vivid colours are 

 subdued and entirely neutral tints assumed." 



Dealing with another, and entirely different, group of butterfly 

 larvae, Scudder observes (op. cit., p. 860) that "some shade of dark 

 greenish-brown is a very common ground tint of the caterpillars of 

 butterflies, and these are often longitudinally striped, as is the case 

 with the larger part of the Argynnids, Vanessids, etc. Here, as before, 

 the stripes are more common in the neighbourhood of the stigmata! 

 line and the dorsal vessel, but they are more commonly broken by the 

 varying intensity of the colours, and are frequently accompanied by an 

 edging, which is but the ground tint intensified at the border. A 

 considerably greater variety is also seen here, from the more or less 

 definite arrangement of the differently coloured papilla 3 in transverse 

 lines across the body, so that, by the combination of these two forms of 

 transverse and longitudinal markings, almost any conceivable pattern 

 may arise, and one which may be highly complicated. Thus a bright 

 coloured spot marks each segment of the abdomen above, in Knvanessa 

 antiopa, giving it a very different aspect from the pepper and salt 



