240 



KNOWLEDGE & SCIENTIFIC NEWS. 



[October, 1905. 



ness which exists between them ? Not many years 

 a -o, entomologists — while perfectly familiar with the 

 fact of this remarkable resemblance — were quite at a 

 loss to account for it. To-day, in the theory of 

 mimicry, we find a very plausible explanation of the 

 problem. 



The hornet is one of those creatures which have 

 been provided by nature with very adequate means of 



1. Th: Hornet trttpa erahro\ 



2. The Poplar ClearwIOK ^Sell^a apiformiMi. 



self defence. It is capable of inflicting painful and 

 even dangerous wounds with its poison-injecting 

 sting ; and, as a warning to its would-be assailants, the 

 hornet has been provided (probably through the agency 

 of natural selection) with a distinctive livery of 

 orange and dark brown. In a former article it was 

 shown that such a livery, possessed by a well-protected 

 species, prevents a vast amount of unnecessary 

 mortality because, by its means, insectivorous 

 creatures are able to determine without " experimental 

 tasting " what insects may be eaten with impunity. 

 Bearing this in mind, it is not difficult to realise that a 

 perfectly harmless insect whose colours and form 

 agreed with those of a well-known harmful one, 

 would be likely to share in the immunity enjoved by its 

 prototype, (iranted that the likeness were sufficiently 

 close, ins<;ct-eating animals would be completely de- 

 ceived by it. 



In the case of the Sesia and the hornet, there is little 

 doubt that this is what actually occurs. The former 

 insect flourishes on the evil reputation possessed by the 

 latter, being mistaken for a stinging insect by the 

 birds, which would be only too glad to cat it did they 

 know it to be a harmless moth. A "lance at the ac- 

 companying drawing from nature will give the reader 

 an idea of how closclv the.se two insects resemble one 

 another in general appearance. The size and shape of 

 its body and wings, together with the arrangement of 

 its colours, combine to give the moth a hornet-likeness 

 which is truly astonishing when the wide differences of 

 structure and habits existing between the two insects 

 is taken into account. 



The order Hymennpitra supplies types for mimicry 

 in many parts of the world. Indeed, it may be claimed, 

 in a sense, that the males of the various stinging 

 species are really mimics of the females and workers. 



For the drones possess no stings, and their " warning 

 liveries " cannot, therefore, have the same direct 

 significance which they possess in the case of the 

 females and workers. 



Species of Hymcnoptera are constantly found to be 

 mimicked by species of Diptcra in a most perfect man- 

 ner. Field entomologists in ICngland will be familiar 

 with the bee-flics {Bombyliin) which, in their hairv 

 covering, general appearance, and the manner in which 

 they hover about a flower, ha\c all the characteristics 

 so familiar in a bee. 



Species of Hcmiptera have been found bearing a 

 striking resemblance to ants, with which insects they 

 company. It cannot, however, be said in what manner 

 — if at all — the bugs are benefited by their likeness to 

 their companions. 



Here it may be said that the mere fact of one insect 

 resembling another to a marked extent docs not neces- 

 sarily constitute a case of true mimicry. There is 

 little doubt that a similarity of habitat and environment 

 conduce, at times, to a similarity of form and colour- 

 ing. Indeed, there are cases on record of insects in- 

 digenous to countries extremely remote one from 

 another, which might well be put forward as examples 

 of mimicry were a similarity of form and colouring the 

 only test. 



Even in the case of similarly coloured insects living 

 in the same country and under similar conditions, the 

 mere fact of a mutual likeness must not be regarded as 

 proof of a mimetic relationship. The two British 

 beetles Triplax aenea and Tclratonta fuiigorum, which 

 belong, the former to the Clavicornia and the latter to 

 the Tieteromera — two widely different families — would 

 be indistinguishable to the novice. Each has a red 

 thorax and bluish black elytra ; each, too, may be found 

 on fungoid growth on decaying trees. Yet, so far as 

 the writer is aware, there is nothing known about the 

 life histories of these insects which would justify the 

 assumption that one is a mimic of the other. It is 

 quite conceivable that a similarity of food, surround- 

 ings and habit may have brought about this strange 

 likeness in colour and form. To establish a case of 

 true mimicry it is necessary to show that one of the 

 insects concerned — the prototype — possesses some 

 dangerous or noxious quality which renders it dis- 



L>tlu^ii /ei ruffinfa. 



tasteful to the majority of its enemies ; and that ilic 

 mimicking species, by agreeing with the special type 

 ol warning coloration concerned, is able to share in 

 the immunity. 



This by way of warning to the young observer, 

 whose enthusiasm might lead him to draw conclusions 

 unjustifiable by fact. At the same time, it cannot be 

 doubted that many very perfect instances of true 



