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the injury inflicted by others. The essentially phytophagous families, 

 that is those families of which the great majority of the species feed 

 upon plants, are very greatly outnumbered by those that are scaven- 

 gers or predaceous or parasitic. If we exclude those that are fungiv- 

 orous, only four families remain that can be classed as preponder- 

 atingly phytophagous — Cecidomyiidae, Trypetidae, Agromyzidae, and 

 Chloropidae ; a few species in these families are predaceous. It must 

 be borne in mind that a phytophagous species is not necessarily in- 

 jurious from the economic standpoint, as many species feed upon and 

 keep in check noxious plants and may therefore be regarded as bene- 

 ficial. 



It is but a step from the phytophagous to the scavenging habit, 

 and in Drosophilidae we find species that may feed upon Cruci ferae, 

 mining the leaves, or in sap exuding from trees and in vegetable 

 refuse. Few other scavenging Diptera feed upon living plants, the 

 only additional exception known to me being those that are fungivo- 

 rous. There are eight families that may be considered as essentially 

 fungivorous — Macroceridae, Bolitophilidae, Platyuridae, Mycetophili- 

 dae, Sciaridae, Platypezidae, Phoridae, and Drosophilidae. Many of 

 the Sciaridae occur in decaying vegetation, while the habits of Phori- 

 dae are remarkably diverse, some being true entoparasites. 



The scavengers belong to more than a score of families. In 

 Muscidae all the species scavenge; but in some other families, An- 

 thomyiidae, for example, we find phytophagous and inquiline species, 

 though these are greatly in the minority and the family is essentially 

 one of scavengers. The Sarcophagidae include some species that are 

 true entoparasites, but the great majority are feeders upon decaying 

 animal and vegetable matter. The scavengers are in the great major- 

 ity of cases really beneficial, transforming dead animal and vegetable 

 matter into such forms as can be utilized as food by growing plants. 

 In reducing the bulk of putrefying substances, which, absorbed by the 

 Cfrowinof larvae, are transformed into the bodies of the resultant 

 imagines, they remove what is noxious to man. It is chiefly when 

 scavengers such as the common house-fly contaminate our food by 

 contact, after feeding on foul substances which are impregnated with 

 disease germs, that there is real danger from these insects. Rarely the 

 screw-worm fly and some of the flesh-flies deposit their eggs or larvae 

 in wounds, either on man or on animals, and in this manner produce 

 serious ulcerations, and the larva of the former has been known to 

 cause the death of persons by penetrating the brain, which it entered 

 by way of the nasal passages. The flesh-flies and some other groups 

 sometimes cause mviasis in man, the larvae finding their way into 



