Leeches 29 



chitinoid material nearly one-eighth of an inch thick, and perforated 

 almost completely at each end by a tubular canal. Lining the spongy 

 layer is a thin membrane of the same material but without spaces or 

 openings. The cavity within is filled with an albuminous mucus 

 similar in appearance and properties to that found within the capsules 

 of earthworms. Imbedded in this are several eggs or young. The 

 exact length of time required for hatching is not known for Macrob- 

 della, but is about three weeks and varies with the temperature. 

 Newly emerged young (figure 14) measuring from five-eighths to 

 three-quarters of an inch long in extension are frequently found 

 during July and August, They are easily recognized as they possess 

 the characteristic color markings and the copulatory glands are dis- 

 tinguishable on examples three-quarters of an inch long. According 

 to Rathbun ('84) this species matures in two or three years in the 

 leech farms. 



While a great deal has been written about the enemies of the 

 medicinal leeches under cultural conditions fifty years ago, when the 

 matter was of considerable economic importance, little of a specific 

 nature is recorded concerning the enemies of our leeches in the wild 

 state. Doubtless predacious fishes are the principal enemies of the 

 developed animals, though the worm leeches {Erpohdella) appear to 

 fall a prey more often than do the jawed leeches. I myself have 

 found them in the stomachs of black bass and sunfish only, and even 

 in these but very rarely. Zoological literature records them among 

 the food of a variety of species. A foreman in the Park, Mr. 

 Herbert, reports that in the late fall of 19 17 he examined the 

 stomachs of several yellow perch taken in Carr Pond, and found 

 them to be filled with large dark colored leeches that he thought were 

 Macrohdella decora. During July and August, especially the latter, 

 Mr. Fletcher and I caught numbers of yellow perch (together with 

 common and long-eared sunfish and catfish) in Carr Pond in the 

 hope of confirming this statement, but in no case were any leeches 

 found in the stomachs. As this perch is abundant and of large size in 

 Carr Pond any general use by it of Macrohdella as food should exert 

 an important repressive influence. That fishes will eat leeches is 

 evidenced by their value as bait. For this purpose their toughness, 

 rendering them difficult to strip from the hook, makes them superior 

 to earthworms and they seem equally attractive, as I have found per- 

 sonally in the cases of sunfish and perch. In many parts of Pennsyl- 

 vania country boys habitually employ Erpohdella and Hcentopis for 

 this purpose, and Macrohdella is said to be so used in the lakes of 

 Minnesota and Wisconsin. Professor T. L. Hankinson tells me that 

 he has employed them successfully, and at the writer's suggestion 

 some of the campers on Carr Pond took up their use to a limited 

 extent. 



Aquatic birds probably destroy many leeches. I have found them 

 in the stomachs of both wild and domestic ducks. It seems probable 

 that small species, together with the eggs and young even of 

 Macrohdella, may often fall a prey to the sandpipers and plovers 



