BODILY CHARACTERISTICS CONSPICUOUSNESS 307 



with inedibility in another Sea- Slug (Pleurobranchus membrana- 

 ceus), which is distinguished by its conspicuous yellow and reddish 

 markings, while its skin secretes an acid. The two examples 

 given will suffice for purposes of illustration, but the bright colours 

 of many other Gastropods, and perhaps also of some bivalve 

 molluscs, may very likely be explained on the same lines. 



Warning Colours of Insects. So many cases have been de- 

 scribed of genuine warnings among Insects of various kind, that 

 the difficulty here lies in the selection of material. Good examples 

 are to be found among those members of the Hymenoptera which 

 possess a sting, as, e.g., Wasps and Hornets, which are rendered 

 very conspicuous by alternating rings of black and yellow. Similar 

 markings and colours are exhibited by many Bees, though in their 

 case red is often substituted for yellow. 



The largest Butterfly to be found in Britain is the Black-veined 

 Brown (Anosia erippus\ an American form which appears to be 

 doing well in the struggle for existence, for its area of distribution 

 is steadily getting wider. The wings are of an orange-brown 

 colour, marked with conspicuous black veins, and edged with 

 black upon which white spots are displayed. The under side 

 is as conspicuous as the upper, contrary to the rule for most 

 Butterflies. This form is known to be distasteful to insectivorous 

 animals, and what is even more interesting, Scudder has shown 

 that its eggs and caterpillars are not attacked by certain parasitic 

 insects that play an important part in keeping down the numbers 

 of many other Butterflies and Moths. 



The Magpie Moth (Abraxas grossulariata] is a good example 

 of a British species possessed of distasteful qualities, and warn- 

 ingly coloured in all three stages of its existence. The caterpillar 

 presents black -and -orange markings on a cream ground, the 

 chrysalis is black with yellow bands, and the wings of the perfect 

 insect are yellowish-white with conspicuous black spots. 



Numerous experiments have been conducted by several natural- 

 ists regarding the edibility or otherwise of a large number of 

 caterpillars, and as the result of these it may be stated as a general 

 rule that insectivorous animals such as Lizards, Birds, &c., reject 

 conspicuously-coloured forms, but eagerly devour those which are 

 more or less inconspicuous in their natural surroundings. It may 

 therefore fairly be concluded that the colours and markings which 

 make certain caterpillars easy to see are of a warning nature. As 



