THE CAUSE OF MIMETIC EBSEMBLAKCE. 579 



their uniformity, are supposed to produce tlie effects. When we 

 are told that common food, common climate, &c. produce a 

 common effect, we liave the means for proof or disproof ia, at 

 any rate, some striking examples ; for we know the food and con- 

 ditions of certain species which, exhibit mimetic or common 

 warning associations. There are many examples of Longicorn 

 beetles mimicking Lycidoe (Malacoderm beetles) in the same 

 locality; but during the earlier stages, m which the appearance 

 of the final stage is determined, the former lives in a burrow, 

 feeding upon wood or the tissue of plant-stems, and sheltered 

 from many of the climatic influences and changes, while the 

 other lives in the open, freely exposed to them all, and sustained 

 by an exclusively carnivorous diet. I owe tbis suggestive com- 

 parison and the Section which arose out of it to a conversation 

 with Mr. C. J. Gahan, of the British Museum, Similarly in the 

 case of S. American moths belonging to the Castniidce, which 

 resemble Ithomiine butterflies (see Section 12, page 598), the 

 larvae of the former burrow in plants, while the latter ai'e freely 

 exposed on the leaves which form their food. 



It is hardly necessary to insist on the importance of the larval 

 stages in this respect. When the imago emerges from the pupa 

 and its expanded wings have dried, it has assumed its permanent 

 appearance, and nothing that it will eat or endure henceforward 

 produces any further effect upon its colours or patterns, &c. 

 Hence identity of food and conditions during the final stage cannot 

 be of any assistance in the interpretation of mimicry. It is neces- 

 sary to point this out clearly, inasmuch as Beddard ('Animal 

 Coloration,' London, 1892, p. 232, footnote) has said, speaking of 

 the resemblance between Eristalis, the drone-fly, and the hive- 

 bee, " It is an interesting fact, in connexion with the resemblance 

 between this fly and a hive-bee, that it feeds upon pollen and 

 honey. This fact may have some significance in relation to the 

 effects of food upon form and coloration." But the larva of 

 Eristalis stores up nutriment, out of which the final form is 

 built, by feeding on putrefying animal matter, a food as different 

 as possible from that provided for the larval bee. The peculiar 

 conditions under which the larvae of stinging Hymenoptera 

 obtain their food invariably contrast strongly with the larval 

 condition of their numerous mimics. We find in this Section, 

 as in the others, that the suggested interpretation of these 

 resemblances as the common effect of a common cause or set of 



