74 FLEAS, FLUKES AND CUCKOOS 



The wound in the host's skin and flesh is inflicted by the maxillary 

 lacinia (Plate XII b) — a pair of sword-hke blades which bear four rows 

 of upwardly projecting teeth on their outer surface. Running along the 

 middle of the inner surface is a gutter or channel. Down this, saliva, 

 containing an enzyme which inhibits clotting of the host's blood, flows 

 into the wound. While feeding, a thin median unpaired rapier-like 

 blade, the epipharynx, lies squeezed between the two maxillary blades — 

 all three together forming a tube up which the blood is drawn by the 

 pumping mechanism in the head. The labium serves to protect the 

 lacinia and bears the labial palps which are apparently organs of touch 

 and are used as such when the flea is selecting a good spot on the host's 

 skin through which to drive the blades. When a flea is feeding the 

 mouth parts become fully embedded in the flesh, the head is drawn 

 down on to the skin of the host, the front legs are tucked back or some- 

 times flexed and held above the body (see Plate XXXIII), and the flea 

 supports itself with the middle and back pair, or only the latter. It is 

 thus tilted sharply forward and appears to be standing on its head or in 

 the early stages of turning a somersault. In the case of the hen stick- 

 tight flea the feeding position is somewhat different. The maxillae stick 

 out in front rather like the proboscis of a tick only not so straight — no 

 doubt a more suitable attitude for a sedentary species to adopt. 



Fleas have a voracious appetite and they have been known to feed 

 for four consecutive hours without a pause. The tropical rat flea which 

 is a particularly fierce feeder, weighs only 0.6 milligrams (or i /40,ooo 

 of an ounce) and the capacity of its stomach is 0.5 cubic millimetres. 

 Only a mere fraction of the blood imbibed is digested. Most of it 

 passes through the flea unchanged and is squirted out drop by drop 

 at the hind end or anus. 



Many beginners, when first examining a mounted and cleared 

 specimen of a flea, have been puzzled by what appears to be a strange 

 patch of bristles in the forepart of the abdomen (Plate XVII). These are 

 in reality a mass of about 800 spines in the inside of the crop or proventri- 

 culus — the only highly specialised portion of the alimentary canal of a 

 flea — which help to crush up the blood corpuscles of the host. 



It is not known if the non-sedentary species of bird fleas have any 

 favourite feeding spots on the host's body. Rat fleas generally try to get 

 a hold between the shoulder blades or on the back of the neck where it 

 is more difficult for the host to kill them. Many wild rodents such as 

 marmots are more frequently bitten on the rump. There is also a 



