236 THE COLOURATION OF INSECTS 



been produced by a portion of the wings enclosed in a 

 bird's bill breaking away, as I have previously described. 

 As for direct evidence, G. A. K. Marshall first collected a 

 number of records of attacks by birds actually witnessed,^ 

 but C. F. M. Swynnerton has recently produced such 

 overwhelming evidence, ^ that there can no longer be any 

 doubt about the matter. His many careful observations 

 have shown that attacks on butterflies may very easily 

 be overlooked unless an observer is especially on the look 

 out for them. 



For instance, the late F. C. Selous said : " I have never 

 once seen a bird eat a butterfly in Africa." {African 

 Nature Notes and Reminiscences, p. 9.) But I do not 

 see that the negative evidence of a hunter, who did not 

 pay so much attention to small life as to big game, weighs 

 against the positive evidence brought forward by Swynner- 

 ton and others, who have paid special attention to birds 

 and butterflies from this point of view. 



In fact, Selous's statement only shows how much an 

 observer may fail to see outside his particular sphere 

 of interest ! 



It appears to me that observation of one class of life 

 renders it difficult to observe another ; indeed, there are 

 three definite fields, requiring radii of observation of 

 different lengths. First, and nearest, are insects whose 

 small size renders it necessary to look for them near at 

 hand. I find that I instinctively keep my vision on objects 

 within about ten yards' radius when I am out in the field, 

 insects being my natural prey. Big game can hardly 

 be expected to be seen within this area ! If it is desired 

 to observe birds, the radius is longer, and one looks not 

 on the ground or low herbage near at hand, but at bushes 

 and trees at least twice as far away, and for mammals 



» Trans. Ent. Soc. Loud, 1902, Part III, pp. 353-71. 

 ^ Proc. Ent. Soc. Lond., 1915, pp. xxxii-xliii ; Journ. Linn. Soc, 

 1919 ; Zoology, vol. xxxiii. 



