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College of Forestry 
CHAPTER VI. ENEMIES OF FRESH-WATER 
MOLLUSKS. 
Since the Mollusca are an important element in the food 
of fish it is of importance to know how they can be pro- 
tected and increased in number. ‘The first step is to know 
their enemies. A large number of animals prey upon mol- 
lusks, using them as food. These animals come into com- 
petition with the mollusk-eating fishes, causing a heavy drain 
on this source of supply. ‘This is compensated for, in a 
measure, by the fact that many fishes live on certain of these 
animals (dragon-fly nymphs, batrachians, ete.), thereby 
receiving the benefit of the mollusks, though secondarily. The 
mollusks are also preyed upon by certain parasites which may, 
in a measure, affect the life of these animals. Some of these 
parasites may occupy the mollusk as a secondary host, com- 
pleting their life cycle in fishes, birds, or other animals. 
While collecting the data embodied in this section, the 
fact has stood out clearly that carefully prepared informa- 
tion on this subject is sadly lacking. In the case of the 
molluscan food of the Reptilia and Amphibia, the records of 
this class of animals from stomach contents are far from 
being as accurate and precise as could be wished. In most 
eases the record is only “clams” or “snails.” It would 
seem of enough importance to have this important class of 
animals more carefully identified. We are aware, of course, 
that such attention to detail consumes much time, but the 
value of the information warrants it. 
1. Prepatrory Insect Enemies. 
Needham and Hart (1901, pp. 17, 47) record the pres- 
ence of mollusks in the digestive system of the nymphs of 
dragon-flies (Odonata). These are as follows: 
Epicordulia, lives in the deeper waters, as the bottom of 
small lakes, where it finds principally a mollusean diet, 
including Amnicola and Physa. 
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