EVOLUTION 373 



morphic species like P. darda?ius does follow Mendelian 

 laws is established, but this does not oblige us to deny the 

 adaptive value of mimicry, which has received strong support 

 from the recent field investigations of G. A. K. Marshall 

 (1902, 1909), C. F. M. Swynnerton (1919), and Hale 

 Carpenter (1920, 1921). 



The value of mimicry to butterflies that display it 

 depends clearly on the danger which they might incur from 

 birds and other creatures, and opponents of the selection 

 theory have often denied that these insects are commonly 

 pursued by predaceous enemies. Mimicry can have no 

 protective value unless insects " w^arningly " coloured are 

 jfor the most part left alone by creatures that freely catch 

 and eat insects not so advertised as noxious. Ever since 

 Bates' observations became well known this generalisation 

 has been affirmed by some and denied by others who have 

 had opportunity of observation ; the long- continued, 

 systematic investigation necessary for deciding the point 

 has only been undertaken in recent years. Experiments 

 in offering various butterflies to birds are largely affected 

 in result by the bird's condition, whether of hunger or 

 repletion, and general statements by observers that they 

 have never seen a bird eat or pursue a butterfly do not in 

 themselves afford negative evidence of any value. As 

 Hale Carpenter remarks, " attacks on butterflies may very 

 easily be overlooked unless an observer is especially on the 

 look out for them." Marshall has collected a number of 

 records on this subject and made careful personal observa- 

 tions in England and in tropical Africa. As might be 

 expected, swallows and flycatchers seize and devour butter- 

 flies constantly. An especially interesting British observa- 

 tion is that the Kestrel swoops on butterflies resting on the 

 ground and seizes them ; in the south of England this 

 small hawk has been watched in the act of taking large 

 numbers of a *' fritillary " {Argynnis aglaia) and the'' Marbled 

 White " {Melanargia galatea). Hale Carpenter records how 

 he watched wagtails in tropical Africa feeding on butter- 

 flies ; a single bird devoured eleven in three minutes, and 



