134 



KNOWLEDGE & SCIENTIFIC NEWS. 



[June, 1904. 



Conducted by F. Shillington Scales, f.r.m.s. 



MITES. 



Cecil Warburton, M.A. 



(Coniinucd from page 105.) 

 Akp now, perhaps, a somewhat more detailed account 

 of the animals we are looking for may not be out of place. 

 That they are not insects, but arachnids, is doubtless 

 perfectly well known to readers of " Kxowledge." They 

 are without antenns, and have normally eight legs when 

 mature. The_ Oribatida are blind, but when eyes do 

 occur in the mite tribe they are simple and not compound. 

 The Arachnida of this country are represented by the 

 spiders, the harvestmen, the " false-scorpions," and the 

 mites. The false-scorpions, or Chelifers, are unmistak- 

 able, and the spiders are distinguishable at a glance from 

 the mites because of the narrow pedicle or "waist " which 

 joins the two portions of their body. The characters 

 which separate the mites from the harvestmen are not 

 quite so obvious, but the latter have the abdomen more 

 or less distinctly segmented, and have always two eyes 

 on a turret in the middle of the fore-part of the body. In 

 practice there is little danger of confusing the two groups, 

 as very few mites, except the easily recognised ticks, are 

 equal in size to the smallest British Phalangids or har- 

 vestmen. All mites live on fluid nutriment, some deriv- 

 ing it from animals, others from plants, and their mouth 

 parts are accordingly adapted for piercing and sucking. 

 It will be useful, perhaps, to give in this place a short 

 review of the principal acarine groups, and to indicate in 

 a few words the general condition of our knowledge with 

 regard to them. 



First of all, then, we have two families of very minute 

 worm-like mites, the Eriophyidre (or Phytoptida-) and 

 the r)emodicida\ The former are generally known as 

 gall-mites, and are responsible for various plant diseases, 

 a familiar example being the disease of " big bud " in 

 black currants, which is caused by Eriophyes rihis. The 

 Demodicidae are animal parasites, and the best-known 

 example is Demode.x foUiciiloriim, parasitic in the hair 

 follicles of man. Then follow the Sarcoptidre, or itch- 

 mites, extremely unattractive creatures, which are external 

 parasites of various vertebrate animals. All the above, 

 possessing a certain economic importance, have neces- 

 sarily attracted more or less attention from those who 

 study the diseases of animals and vegetables, but from the 

 faunistic point of view there is much ignorance with re- 

 gard to them in this country. For further information 

 we may refer the reader to Neumann's " Parasites of 

 Domesticated Animals," which has been translated by 

 Dr. Fleming, and to Connold's handsome volume on 

 " British \'egetable Galls." 



We next come to the Cheese-mite tribe or Tyrogly- 

 phids, which feed chiefly on decaying animal or vegetable 

 matter. They are a small group of soft-bodied mites, 

 generally white in colour, and the British species have 

 recently been monographed by Michael in the publica- 

 cations of the Ray Society. Then follow the Oribatids, 

 with which we are pnncipally concerned in the present 



paper, and they are succeeded by the ticks or Ixodidae. 

 Though their comparatively large size has probably made 

 the ticks the most familiar examples of mites to the 

 uninitiated, yet we are only beginning to know some- 

 thing ^.bout them, and recent investigations in their 

 direction are again entirely due to their economic impor- 

 tance as the medium by which various dread diseases are 

 communicated to man and domestic animals — chiefly in 

 foreign countries. Neumann's " Parasites " may again 

 be consulted, and the same author has written a Revision 

 of the Ixodida;, but the British ticks are only very 

 slightly known. 



The same may be said of the Gamasida?, free-living 

 predaceous mites, examples of which are sure to be found 

 among the moss in which we are seeking the beetle 

 mites. They run rather quickly and use their long front 

 legs chiefly as feelers. A serious attempt to deal with 

 the British species is very much to be desired. 



Other families of free-living mites, also clamouring for 

 attention, are the Bdlellida? or snouted-mites, and the 

 Hydrachnida' or fresh-water mites, and then we come 

 to the Trombidiida?, which include the velvety scarlet 

 " harvest mites," and the Tetranychidre or spinning 

 mites, a familiar example of which is the " red spider," 

 so obnoxious to fruit growers. Almost the only English 

 work which professes to deal with these groups is Murray's 

 British Museum hand-book entitled " Economic Insects 

 — Aptera," a book necessarily long out of date, and not 

 free from grave errors. It is abundantly clear, therefore, 

 that much remains to be learnt with regard to the British 

 Acari, some families of which are practically untouched 

 by any recent investigator. 



And now for a few final words concerning the Oriba- 

 tida8, which afford in many respects the best introduction 

 to the study of the mite tribe. Four stages are distin- 

 guishable in the life-history of these mites — egg, larva, 

 nymph, and imago. In some species the transformation 

 or metamorphosis is very complete, there being hardly 

 any resemblance between the nymph and the imago, 

 while in others the change is not so striking. The eggs 

 are relatively very large, and the larva; which hatch out 

 may be recognised as such by the fact that they possess 

 only six legs. The fully-grown creatures are generally 

 slow moving, and with hard or leathery integuments. 

 Their body is usually pretty clearly marked off into two 

 regions, the cephalothorax and abdomen, though only in 

 one genus, Hoploderma, are these capable of independent 

 movement. Whether a mite is an oribadid or not may 

 be readily determined by examining the cephalothorax, 

 for in this family there is always present a pair of curious 

 sense organs known as pseiidosiigniatic ovf^atis. They are 

 modified hairs, of varying shape, proceeding from the 

 centre of two circular pits with raised edges situated near 

 the sides of the hind part of the fore-body, near the com- 

 mencement of the abdomen. Their peculiar shape and 

 disposition are of prime importance in determining the 

 species of one of these creatures. In the nymplis the 

 legs always terminate in a single claw, but the images 

 may be either monodactyle or tridactyle. The nymphs 

 moult three times before the mature stage is reached, but 

 in some cases the cast skins are never entirely thrown off, 

 and the adult mite walks along with the three nymphal 

 skins still adhering to its back. 



These mites differ very much in the general appear- 

 ance they present, some being smooth, glossy, and beetle- 

 like, while others have a rugged, leathery appearance 

 and are furnished with warty prominences, or bristle with 

 hairs and spines. Some of the more hairy species have 

 a remarkable habit which is a distinct nuisance to the 

 collector. They cover themselves — doubtless for pro- 



