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THE NATURE BOOK 



embodied ; either may be constant or 

 variable. I have aheady given examples 

 of constant protective resemblance in 

 the case of the under surfaces of Butter- 

 flies' \vings, and I need not dwell further 

 on this subdivision. Good examples of 

 variable protective resemblance are to be 

 found amongst vertebrates. The Chame- 

 leon is perhaps the most notorious, but 

 most fish and amphibians exhibit the 

 power of \'arying in tint so as to conform 

 to their immediate surroundings, and 

 many northern animals change colour with 

 the season. In the case of insects it is the 

 Lepidoptera which have been chiefly 

 studied. There appears to be no certain 

 case of a Moth or Butterfly changing its 

 skin, or its spots, after it has once reached 

 the imago stage, but in the larvae of 

 Lepidoptera, and in such pupae as are 

 exposed to the light of day, variation to 

 suit a change of environment is extremely 

 common. Where protective resemblance 

 becomes so specialised as to include form 

 as well as colour, the insects provide us 

 with unique examples, but the greatest 

 care must be exercised to prevent our 

 enthusiasm outrunning our discretion in 

 considering what is or is not a true 

 example of such specialised resemblance. 

 In such cases as the Geometer caterpillars, 

 and the caterpillar and chrysalis of the 

 Purple Emperor, it cannot be reasonably 

 doubted that there is a distinct and 

 specialised resemblance between the 

 insect and a portion of its natural food 

 plant, but in the case of the Orange-tip 

 Butterfly, whose exquisitely chequered 

 wings have led to its being depicted times 

 out of number asleep on the Wild Parsley, 

 I venture to submit that beyond a coin- 

 cidence of form and colouring there is no 

 evidence whatever to establish the con- 

 nection. The umbelliferous plants are 

 singularly attractive to Flies and day- 

 flying Beetles, and singularly unattractive 

 to Lepidoptera. The pattern of the 

 under surface of an Orange-tip's lower 

 wings would conceal it in almost any 

 outdoor situation. I would say much 

 the same of the Brimstone's wings, 

 though I am free to confess that the 

 resemblance between the Brimstone 

 asleep and a young holly leaf is, as has 

 been pointed out by Mr. Kay Robinson, 

 a remarkable one. 



The most amazing forms, however, of 

 specialised protective resemblance come 

 under the heading of protective mimicry. 

 One can hardly help regarding protective 

 mimicry as an immoral phenomenon. It 

 is so hopeless!}' commercial. It is as 

 though one donned a policeman's uniform 

 in order to stand in front of the crowd. 

 The most evident examples of noxious 

 insects in this country are the Stinging 

 Hymenoptera, and there are countless 

 stingless insects which mimic Wasps and 

 Bees, both in coloration and in form. 

 Humble-bee Flies, for example {Bomby- 

 liidcB), are familiar enough to those who 

 study the woods. They are early, short- 

 lived insects (May-June), and may be seen 

 hovering with a characteristic and unmis- 

 takable flight — I have been told that it 

 closely resembles that of a humming-bird, 

 and that the illusion is helped by the 

 length of the fly's proboscis — over some 

 particular patch of ground which takes 

 their fancy. To this they return again 

 and again. In spite, therefore, of the 

 enormous speed and decision with which 

 they change course — I have seen one 

 describe a complete circle flying inside a 

 ij-inch pill-box — they are easily caught. 

 On examining them in the hand, one is 

 at once struck by their flimsiness. Their 

 legs seem hardly to support them, and 

 their weak-kneed appearance is singularly 

 out of keeping with the impression of 

 strength and fussiness which one gathers 

 from observing them in flight. Before 

 rising in the air Bombylius brings his 

 wings into action by a curious manoeuvre. 

 He deflects them suddenly at right angles 

 to their position of rest and imparts to 

 them an extremely rapid up-and-down 

 mo\-ement. Viewed from above at this 

 stage they present the appearance of two 

 rigid black bristles, and are practically 

 invisible against a dark background. As 

 he warms to his work, the extremities of 

 his wings vibrate in " figures-of-eight " 

 in front and in rear of the perpendicular 

 plane, and give one the impression of 

 " buzzing." It is to their fussiness, I 

 fancy, rather than to their colouring 

 that the Humble-bee Flies owe their 

 popular title. So far as colouring is 

 concerned a far closer approach to the 

 Humble-!)ces is afforded by Flies of the 

 genus Volucella. These have no long 



