MITES AND TICKS 189 



mentioned. Many of the Tarsonemini are parasitic on other 

 Arthropoda ahhough the super-family also contains some well- 

 known plant pests. The family Scutacaridae are minute, bizarre 

 creatures found in moss and soil throughout the world, as well as 

 on ants and other insects. One species, Acarapis woodi, infests 

 the tracheal tubes of bees causing the fatal Tsle of Wight disease* 

 found throughout Europe. The mites cause injury by imbibing 

 the hosts' body fluids, and by mechanically blocking their tracheae. 



The behaviour of the red-legged earthmite Halotydeus destructor 

 (family Eupodidae) has been investigated experimentally by Solo- 

 mon (1937) in AustraHa. The dry season is bridged over by resting 

 eggs produced in October. These eggs are laid in great numbers on 

 the surface soil, under clods of earth or sticks and are highly 

 resistant to heat, drought or desiccating winds: moisture and sun- 

 shine are necessary for them to hatch. The adult is a soft-bodied 

 mite whose front legs act as sensory organs. It lives from 25 to 50 

 days, prefers light, well-drained soils and is killed by heat and 

 drought. 



The Tetranychidae include the well-known red-spider mites, 

 such as Metatetranychus ultni, which are probably the most impor- 

 tant economically of all the plant feeding mites. Populations may 

 build up to such fantastic numbers if uncontrolled that trees may 

 be completely defoliated and killed. These mites are often brightly 

 coloured and do damage not only by sucking plant juices but also 

 by spreading virus infections. 



The follicle mites, Demodex spp., are responsible for various 

 skin diseases in man and animals. Usually the general health of the 

 host is not aflFected, but nodules or pustules are caused on the skin 

 which, in the case of cattle parasites, may vary in size from the 

 head of a pin to that of a hen's egg. One species causes red mange 

 in dogs, which is accompanied by a foul and disgusting odour. 

 The Cheyletidae, such as Syringophilus spp., are often found within 

 the quills of birds and are correspondingly elongated, while others 

 have stout claws with which they cling to the fur of mammals. It 

 is probable that they feed on the detritus inside the quills and on 

 the skin. The majority of the family however are free-living pre- 

 dators and have a world-wide distribution. 



Bdellid mites are usually to be found in moss, lichen, leaf mould 



