42 Roosevelt Wild Life Bulletin 



of the unfavorable weather conditions prevailing during the latter 

 part of the summer, projected field experiments were not carried out. 

 It is anticipated, however, that unless employed daily and in large 

 quantity about the swimming places little practical results could be 

 expected. It is probable that the best results could be had in the 

 autumn when the water becomes cold and the leeches sluggish. The 

 experiments with calcium chloride especially indicate that with 

 lowered temperature the toxicity of the solution decreases less rapidly 

 than the \dgor and certainty of the avoiding reaction of the leeches. 

 It seems probable, therefore, that at a temperature approaching that 

 at which the leeches become very sluggish and their senses dull, a 

 point might be reached at which poisons could be applied effectively. 

 Experiments to determine this would be well worth while and if the 

 expectation were justified the method would have the advantage of 

 local applicability if desired. 



Freezing in Winter Quarters. After full consideration of all of 

 the possibilities suggested by the known life history and behavior of 

 Macrohdella decora the conclusion was reached that under conditions 

 existing at Carr Pond the most promising and practicable method 

 of reducing the population of these leeches was offered by freezing 

 them in their winter quarters. Accordingly the following 

 memorandum of recommendations was prepared and forwarded to 

 Mr. Edward F. Brown, Superintendent of the Camp Department: 



" Several species of leeches inhabit the waters of Palisades Inter- 

 state Park. The one complained of by the bathers in Carr Pond is 

 Macrohdella decora, a true blood-sucking leech. This species is 

 moderately abundant in Carr Pond and less so in some of the other 

 lakes. In considering methods for reducing and controlling its num- 

 bers almost every feature of its life history and behavior w^as passed 

 in review and many experiments and observations made. These will 

 be fully detailed in a complete report to be sent to Doctor Adams. 

 All that is required here is to put in writing in a more formal way 

 the plan for dealing with the leech nuisance in Carr Pond that was 

 outlined verbally to Mr. Welch. 



" Strictly speaking, like the frogs with which it so largely associ- 

 ates, this ' blood-sucker ' is a swamp animal rather than a pond 

 animal. Its excursions into the open waters are chiefly in quest of 

 food or new living places. Its home is in the shallows and along 

 the shorelines. This fact was recognized in all of the plans for its 

 control that were considered, and is in large part the basis of the one 

 adopted for recommendation. 



" Two other facts particularly influenced the formulation of this 

 plan. As is true of many other lower animals the activity of leeches 

 is largely determined by the temperature. As the temperature of the 

 water falls with the onset of winter they become more and more 

 sluggish and finally bury themselves in the mud or beneath stones on 

 the bottom in shallow water. At 39° F., the point of the maximum 

 density of water and the general winter temperature of pond water, 

 they are dormant and nearly insensitive. They therefore hibernate 



