234 



PARASITES OF FLIES 



juices of the host. When ready to transform, they leave the fly 

 and cast their skins, the mature mite being a free-living, hairy, 

 scarlet creature about one and five-tenths mm. long. The adults 

 are usually found in the spring and early summer, while the 

 larvae are usually found in the autumn on house-flies and other 

 insects. 



" Mites of the genus Piguieophonis, of the family Tarsoneniidce, 

 have also been taken on house-flies. They cling to the abdomen 

 of the fly, but it is uncertain whether they feed on the insect or 

 use it simply as a means of transportation. The hypopus\ or 

 migratorial nymphal stage of several species of Tyroglyplms 



Fig. ■26. Mites attached to abdomen of Lesser house-fly (from He^\itt, igt-i, p. 61). 



(mites destructive to cheese and other foods), 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. The hypopi 

 most commonly found on the house-fly are those of the common 



^ "When the food supply becomes scarce or other unfavourable conditions prevail, 

 instead of passing through the usual stages of development, the almost fully-grown 

 mites develop hard protective cases or shells into which they can draw themselves for 

 protection. This stage is known as the hypopus, and is in reality a migratorial stage. 

 These hypopi attach themselves to flies and are carried away from the unfavourable 

 conditions, under which probably most of the older mites together with the youngest 

 have perished, to other places where they may encounter food " (Hewitt, 1912, p. 61). 



