DESCRIPTIONS OF ROBBER FLIES OF THE GENUS 



ERAX. 



James S. Hine. 



The predatory habits of robber flies are of distinct value 

 from the standpoint of one interested in economic entomology. 

 A study of the genus Erax has resulted in bringing together 

 nearly all the North American species. As a number of these 

 are undescribcd the following descriptions are published so that 

 the names will be available in future work in the genus. 



Erax planus n. sp. A large, robust species, varying in 

 length from 23 to 30 millimeters. 



Male. Total length, 27 millimeters, antennae black, style nearly 

 twice as long as the third segment, palpi black and clothed with pale 

 yellow hair, face and cheeks with abundance of pale yellowish hairs, 

 ocellar bristles and several bristles on the upper part of the occiput 

 black. Thorax yellow pollinose with most of the hairs and bristles 

 black; wings with a very pale yellowish tinge, costa not thickened near 

 the tip of the auxiliary vein, furcation of the third vein far before the 

 base of the second posterior cell and with a distinct appendage, posterior 

 branch of the third vein reaches the costa distinctly before the tip of the 

 wing; legs clothed with pale yellowish hairs and black bristles, black, 

 except the tibia \vhich are largely reddish. First three abdominal seg- 

 ments dark, mostly with black hair above and white hair beneath, four 

 white with long white hair parted in the middle and directed outward, 

 five, six and seven white, hypopygium dark in color, short and somewhat 

 tumid. 



Female unusually robust for an Erax. Abdomen, except the ovi- 

 positor, uniformly pale yellowish pollinose, ovipositor shining black, 

 about as long as abdominal segments five, six and seven combined. 

 Otherwise colored as in the male. 



Type male from Douglas County, Kansas, 900 feet elevation. 

 (F. H. Snow). 



Several specimens of each sex from the same locality, from 

 Onaga, Kansas, and from Osborne County, Kansas, 1557 feet 

 elevation, collected August 3, 1912. (F. X. Williams.) 



A male from Onaga, Kansas, taken August 20, 1901, is like 

 the other males except that abdominal segment seven is black 

 instead of silver white. This gives the specimen quite a different 

 appearance, but since similar variations have been observed in 

 other species of the genus it is not considered specific here. 



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