280 PRINCIPLES OF ANIMAL BIOLOGY 



Slavery. — Closely related to symbiosis is slavery. Social animals 

 frequently not only hold other animals in bondage, but also protect and 

 serve them. Certain ants, for example, use the secretion of plant lice, 

 and some of the species protect the plant lice in various ways. Because 

 of the mutual advantages in the relation of ants and plant hce, this rela- 

 tion is often called symbiosis rather than slavery. Some ants enslave 

 ants of other species which gather food or even feed their captors. The 

 dependence in the latter case may be very close, some of the slave-makers 

 not being able to feed themselves. 



Predaceous Habit. — Many animals are entirely carnivorous and many 

 which have herbivorous habits are also tlesh-eaters. Flesh-eating forms 

 are frequently restricted in their diet, or at least feed principally upon a 

 limited variety of animals. Thus there are insectivores, or insect-eaters 

 (for example, many lizards which feed largely or exclusively upon insects); 

 true carnivores, or flesh-eaters (as the dogs, which feed upon vertebrates) ; 

 piscivores, or fish-eaters (the fishes whose main diet is fish); and so on. 

 There is much variation in the diet of such predators, but the fact that 

 many forms live exclusively upon animals and that many others must 

 have animal food of a certain kind as well as plant food is an ecological 

 relation of importance. 



Mimicry, — A highly questionable kind of relation based upon the 

 interrelation of animals of different species has been termed 7nimicry. 

 It has been noted that in the same region with certain animals, known or 

 supposed to have exceptional means of defence, are other forms without 

 such means of defence which resemble them very closely. For example, 

 in southern United States the venomous coral snake occurs in the same 

 region as a harmless snake, Cemophora coccinea, which resembles it so 

 closely that the two species cannot be distinguished at a little distance, 

 unless it is known that in the color pattern of alternating rings of red, 

 black and yellow there is a different sequence of colors in the two forms. 

 Other examples are syrphid flies which mimic wasps, and numerous cases 

 among the butterflies. The resemblance is often very close, and may 

 involve both form and color. In each case one of the two forms has, or 

 is supposed to have, some repellent or dangerous property which saves it 

 from attack. The repellent form is regarded as the model, the harmless 

 or defenceless species as the mhnic. 



It has been held that this resemblance is advantageous to the mim- 

 icking forms, on the assumption that they are avoided by their enemies 

 because the latter mistake them for the repellent species, in which case 

 a certain dependence might be claimed. It may fairly be said, however, 

 that an advantage has not been established in any instance. Further- 

 more, the fact that the mimicking form may occur alone, and that in 

 some cases two noxious forms resemble one another very closely, seems to 

 show that the resemblance is fortuitous. 



