OF NORTHUMBERLAND AND DURHAM 185 



plague. It is only necessary to add that the flea, in all cases, 

 becomes infected itself by feeding on an infected animal." 



d. Life Cycle and Note on Rearing Fleas. 



Fleas are not true parasites ; they undergo a distinct 

 metamorphosis and the earlier stages are not attached to the 

 host. The life story is a short and simple one, the cycle 

 embracing the four distinct stages — ^gg, larva, pupa and the 

 perfect insect. In suitable climates the eggs are laid through- 

 out the year, being deposited, a few at a time, indiscriminately 

 on floors of buildings, or in the nest, burrow or haunt of the 

 iiost-bird or animal. The eggs, which are oval or elongated 

 oval in shape, translucent, and, as regards texture, smooth 

 and wax-like, are large when compared to the insect laying 

 them. The larva, a very active creature, is of a dirty white 

 colour, blind, bristle-set and legless, and exists on the varied 

 organic debris of its larval home. The first-stage '• grub " 

 is furnished with a special knife-like spine on the head, which 

 it uses to break through the egg-shell. There appear to be 

 but two larval moults, and at the end of the third stage the 

 larva spins a cocoon in which it pupates, and in due course 

 emerges as a perfect insect. Such, then, is a brief outline of a 

 typical life-history — occupying in all perhaps a month, perhaps 

 six weeks. 



Hints on collecting and preserving fleas are given by 

 both Rothschild and Russell in the above-cited memoirs. 

 Apart from the securing and examining of the various 

 mammals and birds, their nests should be taken and placed in 

 glass-topped boxes, when, by keeping the nest slightly damp the 

 fleas can be reared, and " will frequently keep emerging from 

 their pupae in the nests for six weeks or two months after the 

 nest has been taken." Scrapings from the burrows of animals, 

 and the dung of bats (wherein the larvae of bat-fleas live) 

 should be similarly treated. 



Often a number of quite different animals harbour the same 

 species of flea, whilst predaceous animals acquire the fleas of 

 their prey, a fact that is illustrated more than once in the 



