External Parasites 



227 



The mites live on the skin at the base of the feathers. 



Since the mites are sometimes found on birds which show 



no signs of scabies and since the disease so 



closely resembles favus, which is known to 



be caused by a fungus, it is sometimes 



supposed that this mange is also due to a 



fungus and that the mites are inoffensive. 

 Five species of mites have been recorded 



which live upon the feathers of fowls. 



These are fairly abundant but do no harm. 

 Two mites live within the body of fowls. 



One of these, the air-sac mite, is described 



elsewhere (p. 180). The other, the connec- 

 tive tissue mite, Symplectoptes cysticola, is 



found in the connective tissue of the fowls. 



They produce local irritations giving rise 



to tubercles, but apparently do not affect 



the health of the bird. 



The larvse of the so-called "harvest-bug" 

 (which is not a hugaX all), 

 Tetra7iychus{Throm- 

 hidium) (Leptus) autumnalis, sometimes 

 attacks poultry. The appearance of this 

 mite is shown in Fig. 48. 



This small brick red mite, barely visi- 

 ble to the naked eye, is bred upon berry 

 and currant bushes, vegetables and grain, 

 but when opportunity offers it bites al- 

 most any animal, often attacking man. 

 It sometimes causes considerable mor- 

 tality among late hatched chickens which 



frequent its breeding places. The parasites fasten themselves 



so firmly by their claws and palpi that they can only be 



detached by force. They produce intense irritation, which 



Fig. 47. — .Symplec- 

 toptes cysticola. 

 Connective tissue 

 mite. (After 

 Theobald.) 



Fig. 48. — "Harvest 

 bug," Tetranychus 

 {Leptus) autumnalis, 

 larval form. (After 

 Murray.) 



