INSECT ENEMIES OF EASTERN FORESTS 507 
There is a great diversity of habit in the larval and adult stages. 
Some species are extremely obnoxious to man and animals, some are 
destructive to crops, and others are beneficial. Practically every dip- 
terous family has representatives in the forests, but from a forester’s 
standpoint only a few species are destructive. With some exceptions, 
these species belong to families that are for the most part phyto- 
phagous—the Itonididae, Tephritidae, Agromyzidae, Chloropidae, 
and in part, the Tipulidae. The two last-named families include 
some species that are injurious to field crops, and in the Western 
States at least two species of Chloropidae and one species of Tipulidae 
are injurious to forest trees. Exclusive of certain aquatic Diptera 
(such as mosquitoes and blackflies) and other species that affect man 
or animals (Oestridae, Hippoboscidae, Muscidae, and Metopiidae in 
part), most of the other species are either noninjurious or beneficial. 
Although some of the species of the aquatic Diptera may be a nui- 
sance, they and others are of much economic importance as fish food. 
It is principally the small fish that live on insects, but it must be 
remembered that most fish pass through a carnivorous stage, even 
though they change their food habits later. Experienced fishermen 
are well aware of the attractiveness of certain dipterous larvae as fish 
bait. The larvae of species of tipulids and tabanids are exceptionally 
favored for this purpose. They may be frequently found in abun- 
dance beneath the stones in river beds or under tussocks of grass along 
the edge of a stream, and also in the leaves and debris that collect on 
small dams. 
Scavenging is the most common habit in Diptera. In the family 
Muscidae (used in the widest sense) most of the species are scavengers. 
The predaceous species (such as Tabanidae, Asilidae, and Rhagioni- 
dae) and the true parasites (as Tachinidae, Dorilaidae (Pipunculi- 
dae)) are common. Several families—Sciaridae, Mycetophilidae, 
and Drosophilidae, the species of which are mostly fungivorous—may 
also be included with the beneficial Diptera. 
MEANS OF IDENTIFICATION 
Most authorities agree on the classification of the Diptera, although 
it is admitted that some families are weakly characterized and scarcely 
warrant the standing of families. Until a thorough study has been 
made of the immature stages, however, some doubt as to the true 
status of these groups will always remain. 
Currans’ 1934 revision of Williston’s (434) Manual of North Amer- 
ican Diptera (724) will be found most useful in classification of adults. 
The key to families and genera are simple, and the book is well illus- 
trated. 
Comparatively little is known of the immature stages of the Dip- 
tera, as may be seen from Hayes (272) bibliography of the keys for 
identification. Malloch (287) studied the Orthorrhapha and has 
given a comprehensive key for family separation. Our knowledge of 
the Cyclorrhapha, the species of which often present a marked simi- 
larity, is fragmentary, and the literature concerning it is widely scat- 
tered and often difficult to obtain. At present the key by Brues and 
Melander (68), based largely on food habits, is most helpful. Other 
important contributions dealing with the immature stages of the 
