156 ARACHNIDS AND MYRIAPODS 



at the base of the wings. Later he succeeded iu rearing the 

 adult, and described it as Trombidium tnuscarum. In recent 

 years Oudemans has described Tromhidium muscae from larval 

 mites found on house-flies in Holland. All these forms are minute, 

 six-legged, red mites which cling to the body of the fly and with 

 their thread-like mandibles suck up the juices of the host. When 

 ready to transform they leave the fly and cast their skins, the 

 mature mite being a fi-ee-living, hairy, scarlet creature about 

 1"5 mm. long. The adults are usually found in the spring and 

 early summer, while the larvae arc usually found in the autumn 

 on house-flies and other insects." I have illustrated (fig. 70) a tiy 

 caught in Ottawa in September, 1909, which is infested with this 

 species of mite. 



Howard states further that " mites of the genus Pigmeophorus, 

 of the family Tarsonemidae, have also been taken on house-flies. 

 They cling to the abdomen of the fly, but it is not certain whether 

 they feed on the insect or use it simply as a means of trans- 

 portation. The hypopus or migTatorial nymphal stage of several 

 species of Tyroglyphus has been found on house-flies. This hypopus 

 attaches itself by means of suckers to the body of any insect that 

 may be convenient. The mites do not feed on the fly but when 

 the fly reaches a place similar to that inhabited by the mites the 

 latter drop off, cast their skins and start new colonies." 



Anyone who has collected Diptera as they have emerged from 

 such breeding places as hot-beds, rubbish and manure heaps will 

 have noticed the frequently large number of these insects which 

 are to be found carrying immature forms of the Acari. These are 

 being transported merely by the flies in the majority of cases. 

 Mr Michael informed me that he used to call such flies " the 

 emigrant waggons" — a very descriptive term. Many of these 

 mites belong to the group Gamasidae — the super-family Gama- 

 soidea of Banks (1905). These mites have usually a hard coria- 

 ceous integument. In shape they are flat and broad and have 

 rather stout legs. Sometimes immature forms of these mites 

 swarm on flies emerging from rubbish heaps. Banks holds the 

 opinion that they are not parasitic, but that the insect is only 

 used as a means of transportation. It is difficult to decide whether 

 this is so in all case's. I have illustrated (fig. 71) a specimen of 



