158 Illinois State Laboratory of Natural History. 



never become excessively abundant, being probably 

 a prominent element in the food of the horse-fly larvai. 

 The latter, when washed out of their positions in the 

 soft bottom of shallow waters or in the sand of the 

 margins, float exposed upon the water and become an 

 easy prej' to fishes. A very efficient check on their in- 

 crease is the hjmienopterous egg parasite, which often 

 destroys a large percentage of the eggs in an egg mass. 



The aquatic crane-fly larvae (Tipulidse) feed as a rule 

 on minute algae and the like, but one species observed 

 is in all probability predaceous. Their probable relation 

 to the horse-fly larvae has just been mentioned. I have 

 not observed any hymenopterous parasites upon them. 

 Predaceous Coleoptera and their larvae are often asso- 

 ciated with them and other small dipterous larvae on 

 wet shores. 



The food of the larvae treated under the name Leptidae, 

 I am unable to discuss at present. A careful study of 

 stomach contents is of course necessary before the food 

 relations of the above forms can be definitely and fully 

 described. 



METHODS. 



Collecting.— IrmeciB in vegetation and on or in the 

 bottom were taken by means of a dip-net — a net of 

 about equal depth and width attached to a strong semi- 

 circular ring firmly fixed to a long handle, the straight 

 side of the ring being opposite the point of attachment, 

 (See Plate XV.) For the larger and more active forms, a 

 coarser net of minnow netting was used, and for smaller 

 forms, one made of bobbinet proved most durable and sat- 

 isfactory. To collect from the mud of tlie bottom, the wa- 

 ter immediately over it was violently stirred and then swept 

 with the net. The surface layer of mud was also scooped 

 up in the fine dip-net and then allowed to wash through, 

 leaving the coarser contents in the net. In a similar 

 way, insects on the bottom in deep water were secured 

 by using a dredge, and washing its contents through 



