CHAPTER XVIII 



ARACHNIDA EMBOLOERANCHIATA (CONTINUED) ACARINA HAR- 

 VEST-BUGS PARASITIC MITES TICKS SPINNING MITES- 

 STRUCTURE METAMORPHOSIS CLASSIFICATION 



Order IX. Acarina (Acari, Acaridea). 



Arachnids with unsegmented? non - pediculated abdomen. 

 Respiration by tracheae, or by the general surface of the bod>/. 

 Mouth parts suctorial, but frequently capable of biting or piercing. 

 Metamorphosis always observable. 



THE Acarina or Mites are remarkable not so much for the 

 number of their species, which is very considerable, as for the 

 \.ist multitude of individuals of the Order, which is far in excess 

 of that of any other Arachnid group. This fact is correlated 

 \vith their minute size. Very few Mites exceed half an inch 

 in length, while very many are microscopic creatures, often 

 iiKMsurmg less than the hundredth of an inch. Taken all 

 round, a millimetre may be considered a large size for a Mite. 



There is much variety of habit within the Order. All Mites 

 live principally on fluid nutriment, but it may be obtained from 

 living animals or plants or from decaying organic matter. Some 

 are entirely parasitic upon plants or animals ; others attach 

 themselves to animals in their larval stage, but are free when 

 adults ; while others, again, live an entirely independent and 

 predaceous life. 



The greater number of the Mites are too small to strike the eye. 

 Si une of them have, however, contrived to attract attention, in no 

 very .igreeable manner. Every one knows the Mite popularly called 

 the " Harvest-bug," but to this day there is some uncertainty as to 



1 The single exception is Opilioacarus, see p. 473. 



454 



