CHAPTER XXVII 



PARASITES AND PREDATORS 



JUST as, in the world of humans, there are certain indi- 

 viduals who manage to eke out an existence at the 

 expense of other people, without doing any work or 

 performing any services in return, so, in the world of 

 the lower animals, there are creatures of similar kind. 

 Just exactly what we mean by a parasite ought to be 

 quite clear to us before we go any further. A parasite is 

 a living being which dwells upon or within another living 

 being and derives the whole of its livelihood from its host, 

 as the individual upon which a parasite lives is called. 

 There are semi-parasites or partial parasites and total 

 parasites. The partial parasite is a creature which is not 

 wholly dependent upon its host for its well-being ; the 

 total parasite cannot exist without its host. 



We must be careful not to confuse parasites with guests 

 who contribute in labour or in kind to the well-being of 

 the animals with which they live ; nor even must they 

 be confused with those individuals who share another's 

 dwelling without robbing their associates of any of their 

 goods. Although the term parasite is often used in a 

 derogatory sense, it must not be imagined that all parasites 

 are harmful to man. Many of them are so, it is true, but, 

 again, the activities of many have been harnessed for his 

 benefit. Predators are simply creatures which wander 

 over the face of the earth in search of prey. The tiger is a 

 predator, and so is the lady-bird, and a useful one too. 



Let us first of all consider the doings of a few of the 

 animal predators. We have just mentioned the lady-bird 

 so we will take this little beetle as our first example. It 

 deserves pride of place, for it is an exceedingly useful 



296 



