STUDIES or THE OYSTER DRILL 
109 
bed not by shoveling but by using forks such as are employed by farmers. A forkful 
of oysters is taken up, and before throwing them overboard they are shaken on deck 
a couple of times by dropping them and taking them up again. In this way a good 
many of the drills are shaken off, fall on the deck, and can later be destroyed. This 
method involves no expensive apparatus or excessive time. The only expense is the 
slightly longer time required to throw the oysters overboard. 
( b ) Screening . — A little more expensive than forking, screening is a little more 
efficient. The method is essentially similar to that used to screen sand from gravel. 
The infested oysters which have been dredged and 
placed on deck are allowed to remain in the air for 
several hours. This loosens the drills from the oys- 
ters so that they can be shaken off more easily. 
After this exposure to the air the infested oysters 
are thrown against a screen, the mesh of which is 
sufficiently large to permit the drills to fall through 
but small enough so that the oysters will not. One- 
inch, double-weight-mesh chicken wire answers the 
purpose very well. There are several advantages 
to screening the oysters aboard, providing the boat 
is sufficiently large. It eliminates the expense in- 
volved in handling the oysters; and the screened 
oysters can be thrown overboard, using forks, im- 
mediately after they are screened, thus doing away 
with one more handling. The drills that fall through 
the screen can be destroyed by burning or by drying 
in the sun. 
(c) Floating .- — The effectiveness of this method 
depends on the fact that drills are killed in brackish 
water which, however, is not fresh enough to kill 
the oysters. This method is very efficient, and its 
efficacy warrants its use in heavily infested beds, 
even though the oysters are not to be transplanted. 
The procedure is this: It is first necessary to find 
the exact dilution of sea water which is fatal to the 
drills of a given locality. This is important because 
it has been found that drills taken from various 
regions can sustain different dilutions, depending on 
the salinity of the water in which they were grown. After this has been determined, 
the infested oysters are placed in large cars and kept for about 10 days in waters of 
the lethal dilution. In this way the snails are killed without harming the oysters. 
The method has the further advantage in that it kills not only the adult animals but 
also the small newly hatched individuals, which in other control measures usually 
escape. After the drills have been destroyed, the now uninfested oysters can be 
planted on clean beds. For Hampton Roads the lethal dilution, or death-point 
salinity, is approximately 12 parts per 1,000; for Beaufort, it is slightly higher, about 
14 parts per 1,000. It is important not to crowd the oysters when floating them, 
otherwise a great many will die. 
