REPORT OF THE STATE ENTOMOLOGIST I907 



187 



The following is Mr Ferguson's summary of his results: 



The table shows at a glance that prac- 

 tically all the food of lot i consisted of 

 silt and algae. The explanation for this 

 is that other food, such as midges and 

 worrns was scarce so early in the year. 

 Spring rains had not yet brought down the 

 earthworms. About half of the food of 

 lot 2 was silt and algae, while the other 

 half was pupae and adult midges. In 

 only three of the fish was it possible to 

 say how many midges they contained, 

 hence the stars in the table. Onlv 

 three out of 16 fishes of lot 3 contained 

 midges, while all but four contained 

 earthworms and half of them contained 

 a large amount of silt. Lot 4 shows a 

 large number of adult midges of the 

 genus Chironomus (apparently most of 

 them of the species of which the ap- 

 pendages are shown in figure 4.0) and 

 many earthworms. And one of them 

 contained a single large mass of Chiro- 

 nomus eggs — the only instance in 

 which these were found. Lot ^ shows 

 one adult Chironomus, and earthworms 

 and silt predominate again in lot 6. 



Out of q2 stomachs examined. 38 (41' 

 per cent) contained midges in one stage 

 or another, 27 (2q per cent) contained 

 earthworms, 6 contained beetles, — all 

 adult beetles of nonaquatic habits. 

 Three contained Entomostracans. two 

 contained ants, and only i contained a 

 May flv nymph. This clearly proyes 

 that Chironomus was by far the most 

 important food. 



After discovering the importance of midge larvae in the fo-od of 

 this minnow, Mr Ferguson began a feeding experiment to deter- 

 mine how many such larvae could be disposed of by the fish 

 as a regular diet. He divided. the tank of an aquarium table 

 into two compartments, placing two full-grown Chrosomus in 

 one of them and three others about half as large in the other. 

 A piece of board was kept floating on the surface of each to 

 furnish congenial shadow, and the white enamel bottom of the 

 tank was kept clean so that uneaten food could be found. Midge 

 larvae (nearly all those of Chironomus viridicollis, 



Fig. 4 The mir'ge most com- 

 monly eaten by Chrosomus in 

 Pettibone creek, a caudal ap- 

 pendcges of the adult male, dor- 

 sal view, b one half of tip of 

 abdomen of the pupa, y one 

 half of the caudal fin, and z its 

 fringe 



