DIPTERA OF MINNESOTA. 



CECIDGA/IYIDAE. 



Extremely minute and fragile flies, the maggots of many species 

 causing galls upon plants or trees. Members of the family are there- 

 fore spoken of as "Gall Gnats." Before Malpighi's time, 200 years 

 ago. it was believed that these galls were due primarily to the condi- 

 tion of the plant, and that the maggots therein arose spontaneously. 

 Malpighi, however, advanced the theory, which is in part accepted 

 to-day, that the abnormal growth was due to irritation in the plant 

 tissue caused by a liquid deposited by a female fly at time of egg-laying. 

 These small flies are found in most parts of the globe, from the far 

 north to in or near the tropics, being more abundant in the warmer 

 portions of the earth. There are probably at least 1,000 described 



Fig. 43. A wing of a Cecidomyid. Much 

 enlarged. After' Comstock. 



Fig. 44. Portion of antenna of 

 Xylodiplosis. very much en- 

 larged. After Janet. 



forms, which are being added to each year. The antennae or "feel- 

 ers" are long, and generally hairy, and there are fine hairs over the 

 body and wings of the insects. The antennae are sometimes strik- 

 ingly beautiful. We figure one peculiar form from a Cecidomyid 

 known as Xylodiplosis. In this species the hairs on the antennae 

 have no free extremities, but form loops, as indicated. 



The tiny larvse, or maggots, are of various colors, red or pink, or 

 shades of yellow and orange. Their bodies consist of fourteen seg- 

 ments, which is apparently an exception to the rule that maggots have 

 thirteen segments. A most striking structural peculiarity of almost 

 every species of the family is the presence of a small forked horny 

 piece, with the horns pointing forward, beneath the anterior end, be- 

 tween the second and third segments. It is called the "breast bone," 

 in England the "anchor process," and its use evidently is not known, 

 though it may be analogous with the mentum, the structure having 

 to do with the under lip. Miss Ormerod regarded it as a scraper or 

 digger, to assist in obtaining food from the stems of plants. It is 

 shown in our illustration. 



