ClIEliXES XODOSUS 153 



The inter-relation <>t' the Chernes and M. doiiiestico, h(nvever, 

 is one of no little complexity; much has been written and many 

 diverse views are hcM concerning it. An interesting historical 

 account nf the occurrence of these Arachnids (ni various insects 

 has been given by Kew (1901). Three views are held in expla- 

 nation of the association and they are briefly these : First, that the 

 Chernes, by clinging passively to the fly, uses it as a means of 

 transmission and distribution; second, that the Arachnid is pre- 

 daceous ; and, third, that it is parasitic on the fly. Owing to the 

 unfortunate absence of convincing experimental proof in favour of 

 either of the last two opinions, it is practically impossible to give 

 any definite opinion as to the validity of these views ; nevertheless 

 they are worthy of examination. 



The dispersal theory was held by Pickard-Cambridge and 

 Moniez (1894). Whether the other views are held oi- not there 

 is no doubt that such an association, even if it were only acci- 

 dental, would result in a wider distribution of the species of 

 Chernes, as the flies are constantly visiting fresh places suitable 

 as a habitat for the same. Except in one or two recorded cases, 

 the Arachnids are always attached to the legs of the fly, the chitin 

 of which is hard and could not be pierced, a fact which is held in 

 support of this theory as the only explanation of the association. 



The parasitic and predaceous views are closely related. The 

 Pseudo-scorpionidea feed upon small insects, which they seize with 

 their chelae. It is suggested by some that the Chernes seizes the 

 legs of the fly without realising the size of the latter. Notwith- 

 standing its size, however, they remain attached until the fly dies 

 and then feed upon the body. In some cases as many as ten of 

 the Arachnids have been found on a single fly, and if the move- 

 ments of the insect are impeded by the presence of a number of 

 the Chernes, it will be easily understood that the life of the fly 

 will be curtailed thereby. Pseudo-scorpionidea have been observed 

 feeding on the mites that infest certain species of Coleoptera, and 

 it has been suggested that they associated with the flies for the 

 same purpose, although I do not know of any recorded case of a 

 fly infested with mites canying Chernes also. If this were the 

 case the Chernes would be a friend and not a foe of the fly, as 

 Hickson (1905) has pointed out. 



