56 SOME CRITICISMS [ch. 



forms of P. polytes fly like the non-mimetic one, a 

 mode of flight so different from that of the two models 

 that there is no difficulty in distinguishing them 

 many yards away. Swift flight must be reckoned 

 as one of the chief modes of defence in a butterfly, 

 and on this score the mimic is often better off than 

 the model. And of course it must not be forgotten 

 that where the mode of flight is distinct the protective 

 value of the resemblance must be very much discounted. 



(3) That the imitators are always less numerous 

 in individuals. 



In the majority of cases this is certainly true. 

 Probably all the Old-World Papilios that mimic 

 Danaines are scarcer, and frequently very much 

 scarcer, than their models. This is very evident from 

 a study of the more comprehensive priced catalogues 

 of Lepidoptera. The mimic is generally a more 

 expensive insect than the model, and not infrequently 

 it costs as many pounds as the model does shillings. 

 But the rule is not universal. Papilio polytes is often 

 much more common than either of its models. The 

 remarkable Pierines, Archonias tereas and A. critias 

 (PI. XI, fig. 10) as a rule far outnumber the Pharmaco- 

 phagus Swallow-tail which they mimic. Or again the 

 Chalcosid moth Callamesia pieridoides 1 is a more 

 abundant insect than the Bornean Pierine Delias 

 cathara which it closely resembles. 



It has sometimes been suggested in explanation 



1 See Shelford, Proc. Zool. Soc. 1902, p. 260. A coloured figure 

 of both species is given in the paper. 



