20 



BULLETIIT OF THE BUREAU OF FISHERIES. 



Food of 52 Hydrous larvss taken from pond at Fair port, Iowa. 

 [The figures indicate percentages, the entire food being 100.] 



Chironomus pupse. j| 



1 Caddisfly larvae. |j 



Libellulid nymphs. 



Erythemis nymphs. 



Anax nymphs. || 



Damselfly nymphs. 



1 Crayfish species. |j 



Cypris species. j| 



1 Daphnia species. 



j Hydrous larvae. || 



1 Hydrophilus larvae. |j 



1 Berosus larvae. j| 



1 Philhydrus species, || 

 1 adult. II 



Haliplus species, adult.j 



Gyrinid larvae. 



Dytiscus larvae. 



1 Laccophilus species, 

 1 adult. 



Belostomid nymphs. 



Tadpoles. || 



Fish. II 





























































































































































































10 





20 

























































































10 









1 

























50 





















































































































75 























































































































30 







50 

































10 



























30 





















25 



























50 













































10 







30 







10 



5 







5 









































100 

 10 









































25 

 5 

















































































1 































1 



40 















10 











































































































































30 





















10 



10 





10 













































30 



5 



















































































































































25 











5 



10 











5 





































































5 





































2 



40 



















50 







1 



5 









35 

 30 





























































20 



















10 



10 













50 







































































































50 

























































































100 



































































2 











10 







20 







48 



5 

 5 



10 



""io 



5 







5 





20 



'"26 



10 







5 









3 



1 



1 



10 









10 























1. 25 



1.50 



1.50 



0. 50 0.251 0.75 



1 I 



1.00 



0.60 



0.50 



2. 00 



l.Ooj 1.40 0.60 



1. 30 



3.25 



1. 30 



0. 60 



0. 75 



2.50 



8.25 



Number of specimen. 



Average 40.7 38.25 



From a study of this table several facts stand out quite clearly. 



1. The chief food of the Hydrous larva consists of snails and Chironomus 

 larvse; a mere glance down the first two food columns is convincing proof of this. 

 Nineteen of the 52 specimens had eaten nothing else, 3 others had eaten only 

 Chironomus pupae in addition, and in 4 others these two foods constituted 90 to 

 98 per cent of the total eaten. In other words, half of the larvse had lived entirely 

 upon snails and Chironomus species. Only 2 out of the entire number are credited 

 with having eaten none of these two foods. It is also worthy of note that 4 of those 

 that had eaten nothing else were fully grown. 



