106 
BULLETIN OF THE BUREAU OF FISHERIES 
with its surrounding environment, is confronted with tremendous difficulties. It 
is wise therefore at this time to take up: (1) The factors which are aiding the 
increase of the pest, (2) the factors which might presumably aid man in his combat 
with the animal, and then (3) the means by which man may control or at least pre- 
vent further infestation. 
The soft body of Urosalpinx cinerea is covered by a hard calcareous shell well 
fitted to protect it from the attacks of other animals. Under adverse conditions 
the body retreats into the shell and the opening is effectively closed by a chitinous 
operculum, so that the animal can withstand unfavorable salinities and dessication 
for long periods of time. Besides this structural protection, it is fortunate in having 
no known enemies except itself. 
The spawning habits of the drill insure protection to the embryo, the best 
supply of food for the young, and a means of distribution. The eggs, inclosed in 
leathery capsules, protected from the elements, and supplied with food, are laid 
near or preferably on a bivalve. There being no free living larval stage, the embryos 
remain within the egg case until completely developed and on hatching begin to 
feed immediately. The attachment of the capsules to oysters is of great importance. 
Oyster transplanting usually takes place during the summer months when the drills 
are spawning, so that even though the oystermen remove the adult drills when trans- 
planting from an infested area, the egg cases still remain. A new area is infested 
and in a year or two the new drills cause great damage. 
The size and the adhesive property of the snail are significant in successful 
drill control. Approximately three-fourths of an inch in length, its dull grayish- 
brown color blending almost perfectly with the background, the oyster drill is almost 
completely hidden. It adheres tenaciously to the substratum, making it difficult 
to remove by the ordinary melhods. If this is so, what about the newly hatched 
drills that average from 0.8 millimeter to 1 millimeter (about %5 inch) in length? 
Perhaps the most important factor that prevents successful oyster drill control 
is the practice of transplanting oysters regardless of the presence of drills. Thus 
the oyster planter, by his careless habits, acts as a distributor of this pest, infesting 
new areas daily. 
Against these factors that aid the increase, the distribution, and the destruc- 
tiveness of the oyster drill, we can place the following: (1) The lack of any pro- 
nounced migratory habits and its inability to cross or inhabit muddy areas. (2) 
Temperature, since during the winter months in waters whose temperature falls 
below 15° C. no deeding takes place; when the temperature rises above 10° C. the 
animals are negatively geotropic; they move to the upper surfaces of the oysters 
and are more easily gathered. (3) Females are generally larger than the males; 
therefore in any culling process the probability is that the animals removed will 
be largely females; the significance of this is obvious. (4) The salinity data given 
above shows that the drill can not withstand salinities as low as those which the 
oyster can endure. Oyster spats that occur up the river in waters of low salinity 
are protected from the attack of this pest, and only when man moves the oyster 
seed down into more saline waters, or an unusually dry season occurs, does the 
drill become destructive. 
For the control and removal of Urosalpinx cincerea certain methods are given 
in the following paragraphs. These have already been published in a preliminary 
report. (Federighi, 1930.) 
