326 



The Two-winged Flies 



ish or blacK and red, strong legs, large clear or smoky wings, and stout an- 

 tenna; about as long as head and thorax together and composed of nine to 

 twelve segments. They may be seen often in large numbers Hying heavily 

 over gardens and fields or in woods, early in the spring. The eggs are laid 

 in the soil or in decaying vegetation or in sewers and excrement, the larva; 

 feeding usually on decomposing substances. With some species, however, 

 the larvie feed on the roots of grains or grasses and in this way may do serious 

 damage. BMo tristis, discovered in Kansas in 189 1, appeared in great 

 numbers in wheat-fields and frightened many wheat-growers. As a matter 

 of fact, little injury seemed to be done. B. jcmorata, a common species, 

 is deep red with black wings; B. albipennis, another abundant and wide- 

 spread one, is black-bodied with white wings. A common Californian species 

 appears from the ground in damp woods in great numbers in March. I 

 have watched these flies issuing in countless numbers 

 from the soft lich forest floor in the extensive 

 Monterey pine woods near the Bay of Monterey 



Fig. 454. Fig. 455. 



Fig. 454. — Marrh-flv, Bibio albipennis. (Three ti-ncs natural size.) 

 Fig. 455. — Diagram of wing of Bihio albipennis, showing venation. 



The air danced with them, and the pine-trees and shrubs bore countless 

 myriads on their branches. Professor Needham records a similar sight 

 in which individuals of B. jraternits formed the hosts, and a woodland [)aslure 

 near Lake Michigan was the scene of their appearance. "I have rarely 

 come upon a scene of greater animation than a sheltered hollow in this wood 

 I)resented," writes Profes.sor Needham. "There was the undulating field 

 clad in waving grass and set about with the pale-hued foliage of the white 

 oaks; there were the flowering hawthorns; and there were the myriads 

 of Bibios floating in the sunshine, streaming here and there like chaff before 

 sudden gusts and swirls of air. AH the spiders' webs in the bushes were 

 filled with captives; little groups of ants were dragging single flies away to 

 their nests, and once I saw overhead a chestnut-sided warbler, perched on 

 a bare bough directly in a stream of passing flies, rajjidly pecking to right 

 and to left, persistently stuffing his already rotund maw. I counted a number 

 of flies I could see resting on the grass in several small areas wide apart, and 



