38 BRITISH CICADiE. 



Of the few known species which infest the British 

 Cicadffi, the larval forms of the Trombidiid?e are the 

 most numerous. This Acarine group has represent- 

 atives which show either predatory or parasitic habits 

 on many insects. Even man himself is not exempt 

 from such attacks, as is exemplified in the harvest-bug, 

 or Leptus aiitumnalis of early authors. 



I have the kind permission of Mr. Albert Michael to 

 use some valuable information he gave me on submit- 

 ting to him a few drawings and preparations relating 

 to the Acarine species which infest the Delphacidge and 

 Deltocephali treated of in this Monograph. 



The parasitic habits of these minute Acari have been 

 long known, but it was not at first understood that 

 these hexapod forms were all larvae. They were sup- 

 posed to be adults, and that each species thus repre- 

 sented was imagined to have one host, and one host 

 only. 



Thus, though De Geer evidently considered correctly 

 that many hexapod mites were the young of octopod 

 species, yet he established the different species Acarus 

 phalangii, A. lihellulcG, A. cidicis, and A. aphidis, all of 

 which are really hexapod larvae, and " probably some 

 or all of them are identical with each other." 



The Acarus cicadarum of Goetz is another instance 

 of the same mistake.* 



Scopoli and Hermann also supported the same view, 

 and, again, Latreille erected the genera Z/gj^fi^s and Caris 

 for the hexapod mites, thus perpetuating the same error. 



On the other hand, M. Antoine Duges showed that 

 the above hexapod, Acarus phcdaiigii (the red mite that 

 attacks the w^ell-known long-legged harvest spider), 

 w^as tbe larva of an octopod Tromhidium. But even he 

 supposed the octopod pupa or nymph to be the adult. 



Of late years the subject has been investigated by 

 M. P. Megnin, who has traced the life-history in the 

 cases of Tromhidium fuliginosum and T. holosericeum, 



* ' Bescliaft. d. Berlin. Gesell. Naturforsch. Freunde,' Bd. II. taf. viii. 

 figs. 1, 2, 177G. 



