BRITISH TYEOGLYPHID^E. 



CHAPTER I. 



INTRODUCTORY. 



THE family of Acari, which forms the subject of this 

 book, is a small one as regards number of species. 

 The late Dr. Kramer in the great German work f Das 

 Tierreich/ .only credits it with forty-seven well- 

 established and seven doubtful known species in the 

 whole world ; he divides these into fifteen genera, and 

 although this book will slightly add to the number, it 

 will not do so materially. But, on the other hand, 

 probably no other family of Arachnida contains such 

 an immense number of individuals ; many of the species 

 swarm in such countless myriads where they do occur 

 that the mind shrinks from any attempt to estimate 

 their numbers even in a small space. In considering 

 the number of species it must be borne in mind that 

 the greater part of the world has not been searched 

 for Acari at all, and particularly for such small and 

 inconspicuous Acari as the Tyroglyphidse ; for although 

 by no means the smallest creatures amongst the 

 Acarina, they are unquestionably extremely small. 

 One thirtieth of an inch in maximum length is a very 

 large species, and only one species is known ever to 

 exceed one twentieth of an inch ; other measurements 

 are proportionate, for they are not usually wide in 

 comparison to their length. 



Notwithstanding this small size they are not without 

 importance and interest to man, for they are great 

 destroyers of his property ; their enormous numbers 



