a FLEAS, FLUKES AND CUCKOOS 



The complicated relationship between parasites and their hosts is 

 one of the chief lures of parasitology. As children we puzzled over the 

 old woman who lived in a shoe, but such a situation appears common- 

 place compared with that of the worm which lives exclusively under the 

 eyelids of the hippopotamus and feeds upon its tears. To us, at any 

 rate, the parasite's existence seems strange — whether we are concerned 

 with a threadworm which passes its time partly in a bird's heart and 

 partly in an insect's mouth, or a bed-bug which hides in cracks and 

 crevices, and at night steals out to suck blood surreptitiously from a 

 sleeping beauty's breast. 



It is only during the past hundred years that parasites, in their role 

 as carriers of disease, have stolen the limelight. It is now quite usual to 

 regard insects and ticks as the makers of history, the moulders of man's 

 destiny and as one of the real enemies of the human race. It was 

 possible to see and hear Hitler and Goebbels but it is impossible to 

 perceive the plague bacillus spreading poison or the malaria Plasmodium 

 bursting open red blood corpuscles. The small size of many parasites 

 makes them rather difficult to study. In order to find out something 

 about them it is necessary to spend a considerable amount of time in the 

 laboratory observing minute structural differences between one animal 

 and another with the aid of a microscope, and searching for small and 

 elusive stages of their life-cycle. This work can be both time-consuming 

 and extremely tedious, although at other times it can be exciting and 

 even dangerous — " Image of war without its guilt." 



The most difficult problem to contend with in writing a book of this 

 sort is the fact that most parasites are obscure animals of which the 

 majority of field naturalists know little or nothing. If we analyse the 

 reasons why any particular natural history book strikes us as "very 

 good" we generally find that it has increased our knowledge of a 

 famiHar and well-loved subject. Ford's book on butterflies is an excellent 

 example of this kind. There is nothing new in this observation, for 

 everyone is aware that gossip about strangers is dull, whereas gossip 

 about one's friends is highly delectable. There is a tendency in all 

 human beings, however, to laugh at the discomfiture of others. The 

 thought of a tapeworm as long as a cricket pitch living secretly in the 

 stomach of a film star, or a beetle quietly chewing the feet of a close- 

 sitting hen arouses in us a feeling of macabre amusement. This is, 

 perhaps, fortunate, for it does not matter what initiates the naturalist's 

 interest, so long as it is aroused. Soon interest leads to familiarity and, 



