60 Trans. Acad. Sci. of St. Louis. 



Depending upon adaptation to the parasitic life. 

 Facultative parasites. 



Cheyletiella (?). The species of this genus may not be 

 parasitic at all, but there is evidence that during 

 their immature stages they are real parasites. 

 Some of the Dermanyssidae. 

 Uropoda (Some species). 

 Hemisarcoptes. 

 Obligatory parasites. 



All of the other parasitic Acarina not mentioned under 

 facultative parasites. 

 Depending upon the state of degeneration of the locomotor organs. 

 Capable of walking when off the host. 

 Parasitic Cheyletidae. 

 Oekoiia. 

 Larvae of Rhyncholophldae, Thombidiidae, Hydrachnldae 



and Halacaridae. 

 Ixodidae, Argasidae, Dermanyssidae and the parasitic 



Gamasidae. 

 Vropoda (some species), Cilliha. 

 Parasitic Tarsonemidae. 

 Analgesidae. 

 Canestrinidae. 

 Cytoleichidae. 

 Some of the Sarcoptidae. 

 Eriophyidae. 

 Incapable of walking when detached from host. 

 Many of the Listrophoridae. 

 Most of the Sarcoptidae. 

 Without legs. 



Pimelo'bia apoda. 



Taking into account the nature and habits of the 

 organisms attacked. 



Depending upon whether the organism attacked Is a plant or an 

 animal. 



Phytophaga. 



Most of the Tetranychldae. 

 Tarsonemidae (in part). 

 Eriophyidae. 

 Zoophaga. 



Parasitic Cheyletidae. 

 Gekolia. 



Larvae of Rhyncholophldae, Trombidiidae, Hydrachnl- 

 dae, Halacaridae. 

 Ixodidae, Argasidae, Dermanyssidae and parasitic 



Gamasidae. 

 Parasitic Uropodidae. 



