CHAPTER XVIII 



AKACHNIDA EMBOLOBRANCHIATA {CONTINUED) ACARINA HAR- 

 VEST-BUGS PARASITIC MITES TICKS SPINNING MITES — - 



STRUCTURE METAMORPHOSIS CLASSIFICATION 



Order IX. Acarina (Acari, Acaridea). 



Arachnids with unsegmented,^ non - ^jediculated abdomen. 

 Respiration hy tracheae, or hy the general surface of the body. 

 Mouth parts suctoricd, hut frequently cctpable of biting or piercing, 

 iletamorphosis ahvays observable. 



The Acarina or Mites are remarkable not so much for the 

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

 vast multitude of individuals of the Order, which is far in excess 

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

 with their minute size. Very few Mites exceed half an inch 

 in length, while very many are microscopic creatures, often 

 measuring 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. 

 Some of them have, however, contrived to attract attention, in no 

 very agreeable manner. Every one knows the Mite popularly called 

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



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

 454 



