134 THE DARWINIAN THEORY 



An excellent example is afforded by the Skunk 

 {Mephitis mephitica), a small black and white animal 

 possessing a very offensive secretion, which it ejects 

 over its enemies, and which protects it from their 

 attacks. Owing to this offensive weapon the skunk 

 is seldom attacked by other animals, and its black 

 and white coloration easily distinguishes it from 

 unprotected animals. 



Insects afford many admirable examples of warning 

 colours, and many well-known instances are found 

 among butterflies. The best examples among these 

 are found in three great families of butterflies — the 

 Heliconidce, found in South America, the Danaidcz, 

 found in Asia and tropical regions generally, and the 

 Acrceidcz of Africa. These have large but rather 

 weak wings, and fly slowly. They are always very 

 abundant, all have conspicuous colours or mark- 

 ings, and often a peculiar form of flight ; characters 

 by which they can be recognised at a glance. The 

 colours are nearly always the same on both upper 

 and under surfaces of the wings ; they never try 

 to conceal themselves, but rest on the upper surfaces 

 of leaves and flowers. Moreover, they all have 

 juices which exhale a powerful scent ; so that if they 

 are killed by pinching the body, a liquid exudes 

 which stains the fingers yellow, and leaves an odour 

 which can only be removed by repeated washing. 

 This odour is not very offensive to man, but has 

 been shown by experiment to be so to birds and 

 other insect-eating animals. 



Warning colours are advertisements, often highly- 

 coloured advertisements, of unsuitability as food. 



