214 THE COLOURATION OF INSECTS 



its distasteful qualities are carried through all stages 

 to the perfect insect. I do not know of a case of an 

 aposematic larva of this type becoming a procryptic, 

 and therefore edible, adult. A most typical instance is 

 the Hypsid moth, pactolicus, which is equally conspicuous 

 in all its stages. The caterpillar is ringed alternately 

 with dead black and pure Chinese white, the head being 

 crimson. It feeds fully exposed on a yellow flowered 

 vetch, 1 on which it is visible from far away. When full 

 fed it stretches a few silk threads across and across to 

 make an open hammock, in which it becomes an equally 

 conspicuous chrysalis, fully exposing its light yellow 

 colouring with black markings. The large adult moth 

 is bright orange with steely blue-black blotches, and is 

 one of the most conspicuous insects ; it is of sluggish 

 habit, and rests freely exposed on low herbage, or flies 

 slowly and heavily. The moths of this family are some- 

 times copied by other less favoured insects, and there is 

 little doubt that they are relatively distasteful. 



On the other hand, cases of a procryptic caterpillar 

 becoming an aposematic adult must, I think, be exceptional. 

 I have not yet met with one on the islands. 



A very interesting species is the typically aposematic 

 genus Aletis. These moths are sometimes mimicked by 

 butterflies (see p. 233). One species, A. erici, was found 

 in abundance on Sanga Island in such numbers that the 

 bushes had been completely stripped of their leaves 

 (see p. 103). The caterpillar was tawny orange with black 

 blotches, and was extremely conspicuous ; since many 

 grouped themselves together, hanging head downwards in 

 clusters from the bare twigs, their attitudes accentuated 

 the conspicuous colouring — they had the typical shape 

 of all Geometridae. Inasmuch as the vast majority of 

 Geometrid larvae are procryptic, the ancestral forms were 

 probably so, and the Aletis has been transformed from a 

 ^ Crotalaria striata. 



