524 Mr. G. A. K. Marshall 07i 



defence. Such enemies are numerous enough and 

 deadly enough to make the increased danger of a con- 

 spicuous appearance far greater than any advantage 

 gained by the warning otf of smaller and weaker animals. 

 Such a defence as that of the skunk, on the other hand, 

 appeals to enemies of many classes, and is quite inde- 

 pendent of strength or size. Here and there special 

 animals, probably powerful birds with deficient sense of 

 smell, can endure the defensive odour, and to these the 

 skunk would be an easy prey ; but on the whole the 

 increased danger of a conspicuous appearance and slow 

 movements is far more than compensated by the warning 

 off of an immense number of would-be enemies. Cases 

 like that of the skunk are very common among insects, 

 while those of active defence are very rare. Even the 

 passive defence of a spiny or hairy covering is very 

 different from that ordinarily adopted among vertebrates, 

 because in the insect the hairs and spines are themselves 

 a cause of unpalatability, and often of intense irritation, so 

 that they tend to be associated with an aposematic 

 appearance. It is, howevei*, probable that the intensely 

 hard Rhynchophora with a cryptic appearance, and especi- 

 ally the largest and most powerful Curculioniihe, are 

 strictly comparable with the large number of vertebrates 

 which also unite the methods of concealment with very 

 efficient modes of active or passive resistance. Certain of 

 the largest Curculionidm possessing red marks on a black 

 ground appear to possess an aposematic appearance, and 

 these may be distasteful, although the conspicuous appear- 

 ance may only indicate an excessive hardness and thick- 

 ness of chitin v/hich, coupled with the great size, may be 

 a most efficient defence against a majority of enemies. 

 Mr. Marshall tells me that the largest South African 

 Curculios of the genus Brachycerus, such as B. arpterus, 

 are purely terrestrial, move slowly, and Ireely expose 

 themselves, like our European distasteful species of 

 Phytophagous Timarcha. Under these circumstances the 

 intense black ground-colour and red spots of B. apterus 

 must render it remarkably conspicuous, and it would be 

 of great interest to ascertain, by a number of experiments 

 on many insect-eaters, whether so pronounced an aposeme 

 may indicate hardness alone or hardness combined with 

 some other sjjecial protection. 



The small size of the Brcntliiihc renders it improbable 



