^6 FLEAS, FLUKES AND CUCKOOS 



nostrils of mammals, or round the eyes and wattles of poultry. They 

 then fix themselves by means of their mouth-parts, which become 

 embedded in the skin. When these fleas, male or female, first reach 

 their host they begin to travel against the lie of the fur or feathers. 

 Sooner or later this inevitably leads them to the head (occasionally 

 they take a wrong turn down a leg and finish up between the toes), and 

 when the ears or wattles are reached the shortness of the hair or paucity 

 of feathers no longer produce the feeling of resistance to which the fleas 

 apparently respond, and the females stop moving and fix themselves. 

 It would be interesting to see if shaving a small ring of feathers, say at 

 the base of the bird's neck, would trap the fleas into settling within 

 easy reach of the host's beak. 



It seems highly probable that smell exerts a strong influence on the 

 flea's choice of hosts. It is a well-known fact that not only are horses 

 immune to their bites, but also the grooms who look after them. 

 Apparently no attempt has been made to exploit their dislike of horse 

 smell, and there does not appear to be a commercial insecticide or 

 deterrent with the attractive odour of stables. 



Russian workers claim that fleas have a strong sense of smell and 

 that at a distance of 8 cm. (about 3 inches) they can distinguish between 

 the effluvia of a hedgehog and a mouse, and are also guided back to the 

 host's nest by its odour. 



The field-mouse flea (Ctenophthalmus ag^rtes) even when starving, will 

 only bite man with the greatest reluctance. There is obviously some- 

 thing repellant about him, as far as this flea is concerned, which exerts 

 its influence long before the question of taste comes into play. It is 

 probably smell. 



Fleas are attracted to warmth, and there is a certain temperature, 

 generally around that of the host's body, which they prefer and con- 

 sequently seek. Once a cat flea has found a cat it has also found the 

 conditions in which it is most comfortable and its wanderlust vanishes. 

 It therefore remains on the host. Certain parasites, such as ticks, only 

 feel an urge towards high temperatures when they are hungry. Once 

 gorged they drop off' the host's body. Bird fleas (which, unlike cat 

 fleas, spend most of their time in the nest) may also find the warmth 

 of the host unattractive after they are fully fed and so withdraw into 

 the nests. However, no experiments have been performed to test this 

 theory. 



Many fleas are bUnd but aU the British bird fleas have eyes placed 



