

HANGERS-ON OF MAN 423 



The domesticated and other introduced animals are, 

 besides, responsible for the transportation throughout the 

 world of many external parasites, the majority of which 

 belong to the insect tribes or to the arachnid Mites and 

 Ticks. Amongst the former are such pests as the Ox 

 Warble {Hypoderma}, which ruins over 32 per cent, of the 

 hides of cattle in some parts of America ; the Bot-Fly 

 (Gastrophilus equt] of the Horse, the " Spider-Fly " or 

 "Tick-Fly" of the Horse (Hippobosca equina), the so-called 

 Sheep-Tick {Melophagus ovinus], a two-winged fly adapted 

 to creep on the skin beneath the wool of the fleece, and 

 the Green-bottle Fly (Lucilia sericata], an insect which has 

 become notorious as a destroyer of Sheep, on which the eggs 

 are laid and the larvae feed. There can be little doubt that 

 this species has been carried far and wide with live Sheep 

 or with fleeces ; of recent years it has done much damage 

 in the Netherlands, having been introduced from southern 

 Europe or Asia Minor, though some say from Britain. It 

 has also appeared in Australia, where it "blows" Sheep just as 

 in this country, and in the United States of America, where 

 it has become one of the nuisances of slaughter-houses. 



Amongst Arachnids the introduced pests include such 

 forms as the red Chicken-mite (Dermanyssus gallinae] of 

 domestic poultry, which is common in both Old and New 

 Worlds, the true Sheep-Tick (Lrodes ricinus), now scattered 

 from China to the British Isles, and throughout North 

 America, and the Asiatic-Tick {Dermacentor reticulatus), a 

 transmitter of biliary fever in Horses, which occurs in Europe 

 and northern Asia on most kinds of domesticated animals, 

 and has also been found in England and in Wales on 

 Sheep. 



Other introduced animals have brought their parasites 

 with them, but the significance of such miscellaneous impor- 

 tations is of much less account than the deliberate, sustained 

 and universal dispersal associated with domestic animals. 

 One of the most important of the odd carriers is the Brown 

 Rat (Mus dectimanus), which has borne with it to the utter- 

 most bounds of the earth one or more of the twenty-six 

 species of Fleas which find it a happy hunting-ground, and 

 which include the transmitter of the deadly bubonic plague. 



Even our seas have been enriched by strange aliens 



