18 BULLETIN 841, U. S. DEPARTMENT OF AGRICULTURE. 



tergites and lateral margins of tergites yellow, the size and extent of these markings 

 varying and occasionally the fourth tergite having a yellow band; wings fuliginous, 

 venation dark brown, costa and stigma yellow. 



The female is noticeably larger than the male, and in the field is 

 captured much more easily. 



The characteristic attitude of the adults of either sex while at rest 

 is to lie flat against the grass stem, head downward, the body closely 

 appressed to the stem, the legs not spread but stretched in line with 

 the body while the body itself is concealed behind the closely folded, 

 smoke-colored wings. The ease with which such a strikingly colored 

 fly, while in this position, can escape observation, is remarkable. 

 During the chill of the morning and after sundown this attitude is 

 universally assumed. When basking in the sun at midday, on the 

 warm side of a grass stem, the fly is much less compact, with the 

 wings partly spread and the legs outstretched in order to absorb the 

 utmost of the warmth. Like most Hymenoptera, this species is very 

 partial to sunshine and rarely is seen abroad on a cloudy day. In 

 fact, in cloudy weather it is not easy to find these flies at ail, 

 unless one is entirely familiar with their habits. 



They are weak fliers and seldom travel to any great distance at 

 one time. In Utah they commonly move about among the plants 

 of bunch grass, making short flights from tuft to tuft. If the wind 

 rises or the sun goes behind a cloud they promptly disappear until 

 conditions again become satisfactory. The writer has never taken 

 the adults at any great distance from their breeding places. 



Their hovering flight is peculiar, the swaying motion of their bodies 

 in the air reminding one of certain tipulid flies during their mating 

 air dance. They often hover for a long time to the windward of a 

 grass plant without alighting, seeming to enjoy the motion. The 

 males are on the wing much more than the females, but neither sex 

 will remain in the air while the wind is strong or when it is cool. The 

 adults are not at all timid and can often be readily taken from the 

 grass stems with the fingers. When conditions are favorable for 

 her the female is usually too intent on oviposition to be easily annoyed 

 but if disturbed beyond endurance she quickly disappears, her dark 

 color and slender body enabling her to vanish completely among 

 the vegetation. 



Copulation is very brief, usually lasting less than a minute. No 

 notes were made on the attitude assumed during the operation. 



The species is single brooded, the adults appearing during the 

 spring and going out of existence some time about midsummer. 



The earliest individual met hi Utah was taken in a net April 26, 

 1910, in an alfalfa field. Adults have been seen in the mountains 

 late in July and they probably linger longer than that, ovipositing 

 in such green grass stems as they can find. Near Kimballs, in Utah, 

 September 8, 1911, the writer took very young larva? from stems of 



