PALATABILITY OF SOME BRITISH INSECTS 811 



The second fact has an important bearing upon the criticism 

 sometimes advanced against the theory of warning coloration 

 and mimicry as applied to butterflies, namely, that birds under 

 natural conditions are seldom seen to eat these insects.* Hence it 

 lias been inferred that birds cannot be reckoned as serious enemies 

 of butterflies. Whatever may be the explanation of the circum- 

 stance, I am tolerably sure, from the behaviour of the two classes 

 of animals when pitted against one another, that the inference 

 drawn therefrom is erroneous. The insectivorous birds in our 

 aviaries seemed to know at once what the butterflies were; they 

 were on the alert the moment one was liberated and pursued it 

 with determination and precision, following its every turn and 

 twist, and either catching it upon the wing or pouncing upon it 

 after settling. It is true that this predatory deftness may have 

 been acquired in relation to the chase of insects other than 

 Lejiidoptera ; but unless the birds recognised butterflies in 

 general — a group which cannot be mistaken for other insects - 

 as part of their natural prey, it is difficult to understand their 

 eager excitement at the sight of those J offered them. 



Again, unless the species of butterflies used for the experiments 

 are, or were in the past, habitually preyed upon by birds, 

 whence comes the extraordinary skill the liberated specimens, 

 when undamaged or inexhausted by confinement, displayed in 

 dodging the swoop of the birds in mid-air ? Having repeatedly 

 seen the aim of the pursuing bird baffled by the evasive twist 

 of the butterfly, I cannot doubt that the insect's behaviour was 

 prompted by the instinct to escape an habitual enemy of its 

 species, of the same class and with the same predatory methods. 

 It cannot, I imagine, be seriously claimed that escape from the 

 upleap of insectivorous mammals, lizards, or frogs has been a 

 factor of sufficient importance in survival to be reckoned with 

 in this connection ; and, a fortiori, the modernness of the 

 invention of the entomologist's net puts this instrument of 

 capture out of court for consideration. The evidence, therefore, 

 seems to me to afford the strongest support to the conclusion 

 that the power to dodge in mid air and the instinct to put it 

 in force have been fostered to subserve no other purpose than 

 the evasion of swift -winged insectivorous foes. Perhaps predatory 

 Pompilidae must be regarded as a possible auxiliary influence; 

 but apart from these hymenoptera, I can think of no enemies but 

 birds likely to have persecuted butterflies on the wing to the 

 extent presumably necessary to have guided their evasive tactics 

 to the pitch of proficiency they now exhibit. 



Whatever be the value of this suggested explanation of the 

 facts, the facts themselves remain as I have stated them : — 

 (1) Caged insectivorous birdswhich, so far as is known, have never 

 been fed in captivity upon butterflies, are at once excited by 



* Twice I have seen sparrows, which are not typically insectivorous, chase white 

 butterflies in London. Two birds acting in concert were successful on the Srst 

 occasion ; one single-handed failed on the second occasion. 



[*] 



