386 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. u». 



form efficient barriers to their dispersal. Nearly 3,000 species of 

 crane-flies have already been made known to science and many others 

 remain to be described. Many species are comparatively local in 

 their distribution, but a few species are very widespread, especially 

 HeloMa hyhrida, which ranges over most of Asia, Europe, and the 

 New World, and Dicranomyia longipennis, which ranges in a wide 

 belt around the world in the North Temperate Zone. As in many 

 other groups of insects most of the local species of Tipulidae are 

 very seasonal in their appearance, there being vernal, early summer, 

 midsummer, and autumnal species, as well as others that fly through- 

 out most of the summer, and still others that are undoubtedly double- 

 brooded, one brood occurring in the spring, the second in late sum- 

 mer. The larger number of Tipulidae in the vicinity of Washington 

 are on the wing during the month of June. Many of the larger 

 species of crane-flies, belonging to the genera Tipula and Nephro- 

 totrm^ are of considerable economic importance, the larvae devouring 

 the roots of various plants, often killing the vegetation over large 

 areas. 



Crane-flies inhabit a variety of situations, although, as mentioned 

 previously, most species require wet or moist conditions for their 

 development. The adult flies are commonly met with along streams 

 or in woods where the larvae occur beneath the thick layer of leaf 

 mold. They may be swept from low vegetation growing in such 

 haunts. It may be noted that the situations frequented by crane- 

 flies are usually preferred by species of dance-flies, Empididae, both 

 of these great groups being rare in species or individuals in dry or 

 desert conditions. Many crane-flies are found along cliffs or rocky 

 walls of gorges, such as are found in the various runs along the 

 Potomac. Such forms, as Dicranomyia simulam, D. hadia, some 

 Geranomyia^ Limnophila montana, many Oropeza and others, are 

 found resting on the rocky walls or hanging in crevices or crannies 

 in the cliff's. The species that are found in wet meadows and open 

 swales are largely distinct from the species occurring in woods and 

 in shaded swamps. Moreover, the Tipulid fauna of high, dry upland 

 woods is rather peculiar, consisting almost entirely of many species 

 of the genus Tipula, with very few of the smaller Limnobine crane- 

 flies (as Dicranoptycha, Cladura, etc.). The crane-flies of the bogs, 

 such as are found near Beltsville, and those frequenting cypress 

 swamps, are often peculiar to such situations. The immature stages 

 of these insects frequent a variety of habitats that are indicated in 

 some detail under the various generic accounts in this paper. The 

 authors, on a collecting trip taken July 25, 1915, along the Potomac, 

 by way of Dead, Scott's, and Difficult Runs, secured a total of 48 

 soecies of these insects. When it is considered that the height of the 



