MAY FLIES AND MIDGES OF NEW YORK 77 



may be distinguished from them by their wing venation. These 

 midges are often seen, especially in early spring or autumn, in 

 immense swarms dancing in the air, and are frequently to be 

 found at these seasons upon the windows of dwellings where they 

 are often, perhaps usually, mistaken for mosquitoes. 



Professor Williston relates (1896) that over meadows in the 

 Rocky mountains he has seen them rise at nightfall in most 

 incredible numbers, producing a humming noise like that of a 

 distant waterfall, -and audible for a considerable distance. Most 

 of the species are inoffensive or actually beneficial as scavengers. 

 The group Ce. ratopogon, however, forms an exception, 

 some members of which, known as sandflies, or punkies, have 

 the power of sucking blood, and are particularly troublesome in 

 the mountains, along streams, and at the seashore. The Chiro- 

 nomidae are very widely distributed, being apparently as prevalent 

 and as numerous in the frigid as in the torrid zone. There are 

 about 500 European species, many of which were described by 

 Zetterstedt, from Sweden and Lapland. Of the species hitherto 

 described from North America over one third are from Alaska, 

 Greenland and Hudson bay territory. A surprisingly large num- 

 ber of species are common to both Europe and North America. 

 When the fauna of Asia, Africa and South America is as well 

 known the total number of species will doubtless be increased 



many fold. 



Geological distribution 



One would scarcely expect the delicate, minute flies of this 

 family to be preserved from mesozoic times, yet they seem to be 

 not altogether unknown. Two species referred to Macropeza are 

 figured, one by Geinitz from the Lias of Dobbertin and one by 

 Brodie from the English Purbecks ; two other obscure forms from 

 the English Purbecks are figured under the name of C h i r o n o - 

 m u s ; and Corethrium pertinax and Cecidomium 

 grandaevum of Westwood, from the same beds, appear 

 to belong to this family rather than to the Cecidomyiidae 

 or Culicidae. Rhyphus priscus Brodie, from the 

 English Purbecks, also probably belongs here and not to the 

 Rhyphidae. 



