fa one area near New Haven Harbor. Long Island Sound where the bottom is 

 extremely muddy and devoid of oysters, he finds in the summer that occasional 

 shells of live clams ( Mercenaria mercenaria) that protrude above the mud are 

 completely covered with Eu pleura egg cases and those of Urosalpinx are absent 



CONTROL 

 Introduction 



A synthesis of the available knowledge on the biology of U. cinerea is a 

 fundamental and fruitful prerequisite to an appraisal of methods concurrently em- 

 ployed in its control The factors which contribute to the multiplication and 

 distribution of the species (Federighi 1931c) are strikingly manifested in such a 

 review: (1) the presence of a hard calcareous shell and tightly fitting chitinous 

 operculum which partially protect the drill from predators,- unfavorable salinities, 

 and desiccation; (2) a singular freedom from enemies, except possibly its own kind; 

 (3) a spawning behavior which provides protection and a food supply for the unhatched 

 young in egg capsules; (4) young drills emerge from the egg case already covered by 

 a strong shell and operculum and well equipped to plunder neighboring food organisms; 

 (5) the capacity of a small proportion of young drills to "hitch hike" to adjacent ground 

 on floating materials; (6) a high adaptability of the drill to a wide range of environ- 

 mental conditions; C 7 ) the hibernation of a large proportion of drills buried in the 

 sedimem; (8) firm attachment of egg capsules on or in the vicinity of food organisms ; 

 especially oysters; (9) the fixed adherence of all post hatching stages to living 

 oysters and shell and other substrates during summer and winter months; and (10) 

 the relatively small size and drab coloration of the shell, particularly of recently 

 hatched drills. The majority of these characteristics increase the chances for the 

 dissemination of the species in the management of oysters 



Although the oyster drill appears to possess but few weaknesses in its life 

 cycle, and thus far has rather successfully resisted man's relatively uncoordinated 

 and sporadic attempts to control it, it does display certain character) sacs which 

 singly or collectively are or may be further, employed with profit in combating it: 

 (1) a limited low rate of migration for drill populations as a whole; (2) the tendency 

 of drills to avoid soft muddy bottoms and sandy bottoms devoid of shell and other hard 

 objects; (3) during the colder months of the year a relatively loose adherence of the 

 foot of the drill to the substratum; (4) the possession by the drill of a positive geo 

 tactic response causing it to climb onto objects off the bottom at higher temperatures; 

 (5) oviposition only at. higher temperatures, on oyster beds on oysters and shell on 

 intertidal bottoms on rocks exposed at low tide; <6) the highly permeable nature of 

 the egg case membranes to foreign ions; (7) a relatively long incubation period; 

 (8) fatal effect of low salinities which are endured by the oyster; (9) a strong 

 selective response of drills to the ectocrines of some prey, and possibly to the ex- 

 tracts of these; (10) larger size of the females than of males 



103 



