DIPTERA— HELOMYZID^. 43 



that they average easily 3 or 4 and at times even 12 or 15 to the square 

 foot for considerable areas of the walls. L. latens does not commonly 

 occur in any abundance far above the floor of the cave, but congregates 

 on overhanging surfaces under the arches of low side-holes in the wall, 

 on the under side of projecting angles, and in similar places where there 

 is considerable moisture. L. latens is not often seen under a stone and 

 is not attracted to bait. It is probably less sluggish in its habits than 

 0. fenestralis, but does not crawl rapidly and seldom takes flight. The 

 presence of light for a short time or of the hand near is not sulflcient to 

 cause it to stir at all. Nothing short of actual contact with a foreign 

 object or heat from a lamp stimulates it to motion. When it is caused to 

 move it crawls slowly away and if continually disturbed may occasionally 

 be induced to fly. Usually, however, it will not fly unless forcibly dis- 

 lodged and falling through the air, and sometimes it will not take wing 

 even then. Bright light, if thrown upon it for a time, usually causes it to 

 move, in many cases individuals turning squarely about and crawling 

 away from the scource of light. Some individuals, however, paid no 

 attention to the-light, even when exposed to it for an hour or more. 

 I have been unable to determine the food of this species, nor have I 

 identifled its larva or pupa, although among hundreds of dipterous larvae 

 found in decaying meat in the cave some, I am confldent, were larvae 

 of this species. 



The excessive abundance of this species in early summer is probably 

 due to its breeding more abundantly then, although it may breed in the 

 cave at all seasons. The apparent increase in numbers may be partly 

 due to individuals entering the cave from outside with the coming of 

 summer. This species is particularly infested with mites. Sometimes 

 nearly every fly has some of the parasites and some individuals as many 

 as 30 or 40. The parasites collect upon the back of the abdomen and 

 thorax and fasten themselves to all vulnerable parts of the body. 



Taken in Twin Cave, where it is abundant. It was found outside 

 Mayfield's Cave, under chunks of wood in the ravine near the mouth. 



Lerla defessa (Osten Sacken). 



OsTEN Sacken, Bull. U. S. Geol. and Geog. Surv., vii, vol. iii, No. 1, 168. Packard, 

 Mem. Nat. Acad. Sci., iv, 1888, 15, 17, 21, 80, 132 (Mammoth, Wyandotte, Carter, 

 and Hundred Dome caves, and several smaller caves near Glasgow Junction, Ken- 

 tukcy. New Market Cave, Virginia, and a cave at Manitou, Colorado) . Blatchley, 

 Rep. Ind. Geol. Surv., xxi, 1896, 188 (Wyandotte Cave). Aldrich, Cat. N. A. 

 Dip., 1905, 573. 



Common throughout the main passage and larger side-passages of 

 the cave. It is most abundant from "25" to the mound, but is found 

 scattered throughout the cave, except in the driest portions. This 



