STUDIES OP THE OYSTER DRILL 
107 
Two problems confront the oysterman in combating this species: (1) The removal 
of drills from areas already infested, and (2) the prevention of the infestation of new 
areas. 
METHODS FOR REMOVAL FROM INFESTED AREAS 
(a) The trap dredge. — As is seen from the illustration (fig. 6) the dredge consists of 
a wire cage open in front and fitted with an inclined screen. The dredge is dragged over 
the infested oyster bed; the oysters are picked up by the blade at the edge of the 
dredge, moved up over the inclined plane, and the drills automatically screened, 
falling into the cage below while the oysters pass over and fall back onto the oyster 
bed. In this way the dredge can be dragged over great areas, without involving the 
removal of the oysters from the bottom. The dredge is quite satisfactory, provided 
the oyster population is not too dense. 
The most effective time for dredging is the early spring when the animals have 
become active and are on the upper layers of the oysters, but before spawning begins. 
If it is done at this time the females are removed before they have spawned and so 
the young are eliminated. Furthermore, dredging during this season is more effec- 
tive than in the winter months, since, when active, the animals creep to the top 
and are more easily accessible. The proper time for dredging at Hampton Roads is 
the latter part of March; for the Beaufort region the best time is the early part of 
March. 
(b) The use of small concrete pillars. — Small concrete pillars, easily handled by 
one man, may be set out over the infested areas. These pillars, providing surfaces 
higher than the surrounding area of the oyster beds, act as traps because the animals 
congregate upon them, owing to their tendency to creep upward. After three or four 
days they are taken up, the drills removed, and the pillars set out again in new places. 
If the area is below low-water mark, lines and buoys can be attached to the concrete 
blocks, thus facilitating removal and replacement. Pillars of the size shown in the 
illustration have collected as many as 500 drills in three days from experimental 
tanks which were heavily infested. Although no field observations have been made 
with concrete blocks, sand-filled buckets placed on infested beds have collected a 
great many drills. 
(c) Dredging with an oyster dredge fitted with a small-mesh bag. — This method 
is practicable only if the infested oyster bed is being dredged for oysters which are to 
be marketed and if the oysters are all to be taken up. The procedure is as follows: 
After most of the oysters have been taken up, the bed is worked with a dredge having 
a very small-mesh bag. In this way the drills, shells, and other debris are taken up 
and can later be disposed of by burning or drying in the sun. It is important that the 
infested bed be gone over carefully with such a dredge. After this has been done, 
uninfested oysters can be planted in such a locality without fear of loss from drills. 
METHODS FOR PREVENTING DISTRIBUTION 
The solution of the problem of the further distribution of the pest is not as difficult 
as that which involves the cleaning of infested areas. Because the drill is almost 
nonmigratory the infestation of new areas is easily controlled. The oyster planter 
must be careful not to plant infested oysters in noninfested areas. Before doing this 
it is necessary for him to remove as many of the drills as he can by use of methods 
described below. 
(a) The use of forks. — This method is inexpensive and simple. After the infested 
oysters have been put aboard the oyster boat, they are thrown overboard onto the new 
