30 Roosevelt Wild Life Bulletin 



that habitually feed among the shingle and shore debris where small 

 leeches especially abound. 



Rats, minks, small herons, kingfishers, crows, turtles, snakes, 

 crayfishes and various kinds of predacious insects and their larvae 

 may exert some influence, as they were known to do on the leech 

 farms. Among other leeches, the large Hcemopis grandis, which is 

 plentiful in association with Macrobdella decora in Carr Pond, is 

 undoubtedl}- an important enemy of the latter. This leech habitually 

 feeds upon earthworms, smaller leeches and insect larvae, and has 

 been observed to devour Macrobdella decora two inches long. As 

 it lives in the very places where Macrobdella deposits its egg-capsules 

 it is probable that it destroys large numbers of the newly hatched 

 young of Macrobdella. 



METHODS OF CONTROL 



In the effort to devise a practical solution of the problem every 

 know^n aspect of the life history, habits and reactions of this species, 

 of which a general outline has just been given, was passed in review 

 in the hope of finding a weak spot at which it could be successfully 

 attacked. ^lany methods were considered and experiments tried, 

 the most important of which Avill be described. 



Baiting and Trapping. In my previous experience in collecting 

 blood-sucking leeches frequent use had been made of baits of freshly 

 killed and bleeding small animals and of slaughter-house blood placed 

 in a muslin bag dragged through the water or simply placed in the 

 water and allowed to diffuse. This latter was a method of feeding 

 leeches largely employed in the days of hirudiculture. Both of these 

 methods had been found effective in attracting them, and large num- 

 bers of Macrobdella and other leeches were often gathered in a short 

 time by simply catching them in a dip-net as they swam toward the 

 baits, or b}- picking them by hand after a number had attached them- 

 selves to the bag or dead animal. It was thought if such baits were 

 placed in a trap easy of entrance but difficult of exit for the leeches 

 that considerable numbers could be gathered automatically and dis- 

 posed of. Indeed, before visiting the Park this method had appealed 

 to me as likely to meet with success. As soon, however, as I saw 

 the size of Carr Pond and the actual conditions existing there I lost 

 faith in its practicability. Nevertheless a series of experiments with 

 baits and traps, partly in the laboratory, partly in the field, were 

 decided upon. 



Three forms of traps were devised and tried. The first (figure 15) 

 was constructed on the well-known principle of the lobster pot. It 

 is a box 24X i8x 18 inches built of light, matched partition boards 

 with the top hinged to afford access to the interior. The front has 

 the form of a deep reentering angle (figure 16) running the entire 

 length of the box. The pieces composing this angle fail to meet a^t 

 the apex, leaving a slit one-fourth inch wide which is continued by two 

 parallel boards as a passage of the same width four inches further 

 into the interior, thus giving the effect of a horizontally extended 



