Insects 185 



natus Bigot. It has since been rather ambiguously set forth by 

 Mr. C. R. Jones (Contr. Knowl. Syrphidae Colo., 1922) as M. 

 tristis cockcrelli. The species of Cheilosia, of which we have 

 seven, live under the bark of coniferous trees, often causing 

 damage. The larvae of Volucella are scavengers in the nests of 

 bees, and the adults are often very similar to the bees in appearance. 

 Very similar to Volucella in appearance, and also liable to be 

 taken for bees, are the species of Eristalis, the larvae of which 

 are called rat-tailed maggots. They live in water or wet mud, 

 and have a long tail-like respiratory tube. The Onion-fly, Eumerus 

 strigatus of Fallen, is a native of Europe, recently introduced into 

 America with bulbs. When it appeared some years ago at Fort 

 Collins, it was not unnaturally taken for a native insect, and 

 was described as Microxylota robii Jones. For a full account of 

 the Colorado Syrphidae see C. R. Jones in Annals Entom. Soc. 

 America, 1917, and Bulletin 269, Colorado Agricultural Experi- 

 ment Station (1922). 



The Oestridae, or Bot-flies and Gad-flies, include the stomach 

 bot of the horse (Gastrophilus intestinalis) , which was reported 

 from Colorado by Osten Sacken as early as 1874; the Ox-bot or 

 Warble fly (Hypoderma lineata) ; and the very large stout flies of 

 the genus Cuterebra and Bogeria, the larvae of which infest rab- 

 bits, rats and mice. The Warble fly lays its eggs on the hair of 

 cattle, and the larvae locate under the skin, causing swellings 

 known as warbles. They eventually escape through holes and 

 pupate in the ground. The loss from these insects, especially 

 to the leather industry, is so enormous that plans have been 

 discussed for concerted action all over the country, in the hope 

 of exterminating the pest. 



In the Green River Shales of Western Colorado fossil bot-fly 

 larvae (Lithohypoderma ascarides Scudder) are extremely numerous, 

 but their history and origin puzzle all investigators. Is it possible 

 that the waters were saline, and the heavily infested animals (of 

 what species we have no knowledge) found that they would 

 cause the larvae to leave the warbles? 



The family Tachinidae is a bewildering complex of closely 

 related genera and species of bristly flies, parasitic on various 

 insects in the larva state. The group is thus extremely beneficial 

 to man, especially as keeping down the multitudes of caterpillars 



