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 larvffi of the so-called "harvest-bug" 

 (which is not a 6 »(/ at all), 

 Tetranychus{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. 



Fig. 48. — "Harvest , ^ , ^ •+ «■ ■+ u-* 1 



bug," Tetranychus but whcu Opportunity oiiers it bites al- 

 (Leptus) autumnalis, mogt ^nv animal, often attacking man. 



larval form. (After _ . ■ i i i 



Murray.) 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.) 



