SURROUNDINGS OF GROWING INSECTS 233 



its segmentation vividly marked by transverse bands of black 

 and yellow, found feeding on ragwort in summer ; the " looper " 

 larva of the " Magpie " (Abraxas grossulariata), cream-coloured 

 with black and yellow blotches, a familiar object on gooseberry 

 and current bushes in May and June ; or the large caterpillar 

 of the Spurge Hawk-moth (Deilephila enphorbiae) with its harle- 

 quin particoloured livery of patches and spots In this last- 

 named case inedibility seems associated with the poisonous 

 nature of the food-plant (Euphorbia) ; in other cases the 

 larvae secrete a poisonous or noxious repellant which is itself 

 a protection against being eaten, its presence advertised by 

 the brilliant " warning " colour. 



A far larger number of caterpillars are, however, coloured 

 on the opposite principle so as to be hidden through their 

 harmony in tone with their surroundings. As these are greedily 

 eaten by many birds as soon as perceived, it is believed that 

 the concealment that they secure through their likeness to their 

 environment is of value in preserving them from detection 

 and destruction, and the likeness is defined as " pro- 

 tective " resemblance. 1 Most caterpillars which feed on leaves 

 or crawl along twigs are green or brown in colour ; often the 

 green area is interrupted by a pale longitudinal stripe on each 

 side, and in very large caterpillars such as those of hawk-moths 

 (Smerinthus) , for example, the green area is broken by a series 

 of oblique yellow lines. Such a caterpillar, when feeding, is 

 remarkably inconspicuous. Man}/ of the " looper ' cater- 

 pillars are wonderfully like the twigs of their food-plants in 

 shape as well as in colour, and this resemblance is accompanied 

 by the habit of stretching the body stiffly out at an angle to 

 the twig grasped by the prolegs on the sixth and tenth 

 abdominal segments. Thus the larva's mode of behaviour 

 co-operates with its appearance to produce the protective 

 resemblance. It has been shown that many of these protec- 

 tively coloured caterpillars can be induced to change their 

 colours within limits, if they be transferred at a stage 

 sufficiently early from one food-plant to another with leaves 

 and twigs of a different hue ; and these changes are due to 

 a reaction of the subcuticular tissue to the quality of the rays 



1 E. B. Poulton : " The Colour Relations between certain Lepidopterous 

 Larvae, etc., and their Surroundings ". Trans. Entom. Soc., Land. 1892, 

 1903. 



