36 Roosevelt Wild Life Bulletin 



collecting along the shores would be facilitated by placing boards at 

 the edge of the water for the leeches to gather under. As other incen- 

 tives to gathering the leeches may be suggested the offering of prizes 

 and instruction in their use as bait. Little could be expected from the 

 crudely improvised tackle and haphazard methods of fishing of the 

 smaller boys, but for the older boys and camp leaders with their 

 better tackle and greater expertness, leeches can be recommended as 

 a most effective and a satisfactory bait for bass, yellow perch, the 

 larger sunfishes and similar fishes. 



The eggs of Macrohdella are encased in spongy capsules (figure 

 14) deposited for the most part in the mud and turf at the water's 

 edge. Occasionally considerable numbers of these are found in f avor- 

 a^ble spots. It was hoped that at Carr Pond the leeches might congre- 

 gate at locaHzed breeding grounds where the egg-cases would be 

 found in large numbers. This hope was disappointed, however, and 

 only a very few widely scattered capsules were found. Under these 

 conditions collection and destruction of these would be futile. It is 

 doubtful if any physical means for destroying the &gg capsules in 

 large numbers could be applied successfully, as they are very 

 resistant to drying out and to mechanical and chemical injury. 



Use of Natural Enemies. As stated above, very little of a specific 

 nature is known concerning the natural enemies of native American 

 leeches, and particularly of Macrohdella decora. It may be safely 

 assumed, however, that the American counterparts of those animals 

 which have been ascertained to prey upon the European medicinal 

 leech will prove to be factors in the restriction of ours also. As many 

 of these are represented in the fauna of Carr Pond, collectively they 

 doubtless exert an important influence in keeping the blood-sucker 

 and other species of leeches within numerical bounds. Probably the 

 most important of such enemies in Carr Pond are certain species of 

 carnivorous fishes (sunfishes, yellow perch, black bass, etc.), the 

 spotted sandpiper, green heron, belted kingfisher and wild ducks, 

 water snakes, frogs and newts, predacious insect larv'ae, especially 

 Dytiscus and some of the larger dragonfles, and the large toothless 

 leech. Nothing is known of the diseases of wild leeches, though in 

 confinement the mortality of the medicinal leech through infection is 

 very considerable. Doubtless little can be done to combat the leeches 

 through the further use of natural enemies, inasmuch as it is prob- 

 able that a balance between all of the interacting factors has been 

 or soon will be reached and maintained. Some repressive effect 

 might be had by encouraging the increase of certain desirable species 

 of fishes such as those mentioned above, or by introducing crayfishes, 

 of which I saw no examples in Carr Pond; or by destroying their 

 shelters by clearing up the shorelines of boards, logs, etc., as was 

 done among the measures taken against mosquito breeding. How- 

 ever, owing to the activity of the leeches and the ease with which they 

 can adapt themselves to the abundant places of concealment the 

 latter would probably avail little. 



