386 DIPTERA. 



more tough and resisting." The larvae of one genus sometimes 

 live gregariously with those of other genera. Thus Osten 

 Sacken found that the " larvae of Sciophila appeared in a de- 

 caying fungus only after the transformations of Mycetophila 

 were entirely completed. For two or three weeks the eggs of 

 the former remained apparently dormant among the bustle of 

 so many larvae of the other species." (Osten Sacken.) Leja 

 resembles Sciophila in its habits. The larvae of Sciara have 

 no bristles on the tubercles of the under side of the body, usu- 

 ally present in the family. They are more gregarious than 

 the other genera, and have the singular propensity of sticking 

 together in dense patches, generally under the bark of trees. 

 When fully grown they sometimes march in processions in a 

 dense mass, sometimes several feet long, and two to three 

 inches broad, and half an inch in thickness, whence the Ger- 

 mans call them " Army- worms." To the same genus belongs 

 the S. (Molobrus) mali of Fitch, the apple midge, whose larva 

 is glassy white and devours the interior of apples. 



Professor E. D. Cope describes in the Proceedings of the 

 Philadelphia Academy, 1867, page 222, a procession of a spe- 

 cies of Sciara observed in September by William Kite, in Ches- 

 ter County, Penn., where he had observed this army-worm for 

 three consecutive years. "This company (consisting by rough 

 estimation of about 2,400) extended over a length of about 

 twenty-two inches, with a breadth of from three-fourths of an 

 inch in the thickest part, to about one-eighth of an inch at the 

 head, and one-tenth at tail ; five or six worms deep in thicker 

 parts. They advanced at the rate of four inches in five 

 minutes, the hinder ones working their \\MV over the top of 

 the rest." These larva 1 were about one-half an inch long. 

 semitransparent, with black heads. Mr. Kite obsened r.nother 

 procession July 8th, which was six feet six inches long. These 

 trains were attacked l>v larva 1 of Staphylinids. ants, dipterous 

 larva? and other pivdaceous insects. Seven other persons in 

 this country have witnessed similar trains, one of which was 

 observed in Lee, Mass. 



The larva of Mycetobiu, which agrees closely with that of 

 Rhyphus, is found living in pntiVseent sap under the bark of 

 the elm tree. We have found, through the summer, great mini- 



