74 REPORT 108, U. S. DEPARTMENT OF AGRICULTURE. 



tures. Miss Foa has claimed that the forms which, according to Berlese, are stages 

 in the life history of Holostaspis marginafns Herm.. belong to five distinct s}:)ecies, 

 viz, H. marginatus Herm., H. badius Koch., H. raerdarius Koch., //. coiifusus Foa, 

 and H. submarginatus Foa, the last two new species. A great many species of Para- 

 sitidse are found attached, often in great numbers, to various beetles; the coprophagous 

 and xylophagous beetles are especially infested with them. Many of these mites 

 when attached to insects are in an immature or nymphal condition, and do not prey 

 upon the beetle, but use it as a means of transportation. It appears that when there 

 is a considerable increase in a species of parasitid mite living in a restricted place, 

 as a rotten log, some specimens have the migratorial instinct which leads them to 

 cling to any moving object; thus, attaching themselves to a beetle that has bred in 

 the log, they are reasonably sure of being transported to a similar locality where they 

 may start a new colony. Most of these mites cling to the host by their feet, bat in 

 Uropodn and allied genera the mite secretes matter from two glands flanking the 



Fig. 141. — Pneumonyssus simicoJa, Fig. 142.— Larva of Pneumonyssus 



from below. (Author's illustration.) simicola. (Author's illustration.) 



anus which hardens into a pedicel holding the mite fast to the host. Probably the 

 mite is able to loosen at will by the secretion of fresh matter. These nymphal Uro- 

 podas thus attached are called nympha pedunculata. It was formerly supposed 

 that all these mites were predaceous upon their hosts, and the Uropoda vegetans De 

 Geer was considered a highly beneficial mite for destroying the Colorado potato 

 beetle. There are, however, some parasitids that do feed on the host insect, but are 

 not attached to them. Such forms are very common on tropical beetles. Some 

 parasitids live in decaying substances, either animal or vegetable. It has been 

 shown that certain Uropodiiiae live on minute plants, bacteria, and small fungi. 

 Most si^ecies prey on small insects, thysanurans, and other mites, as Tyrogh-j^hidae and 

 Eriophyidae, and occasionally they will eat one another. The food habits of many 

 are unkno -vn, but from their occurrence they are commonly supi)Osed to be predaceoua. 

 There are a few parasitic forms. The entire subfamily Denuanyssinae is parasitic 

 on birds, bats, rodents, etc. Three genera of the true Parasitidne are i)arasitic — 

 Haemogamasus on moles, Laelaps on various small mammals, and Raillieiia in the ears 

 of various animals. A great many occur among decaying fallen leaves. A number of 

 8i)ecies have l)eeii taken in ants' nests. Some of these live at (ached to the ants and 

 obtain food from them. One species is so found on a Scolopcndra. The relationship 

 of the other forms to the ants is not chuir in all cases. It has been shown by Michael 

 that some species of Hypoaspis feed uj)ou the dead ants. It is therefore probable that 



