100 
BULLETIN OP THE BUREAU OP FISHERIES 
planted bed, having only young spat, would show almost all right valves perforated. 
On the other hand planted beds where oysters average 2 to 3 inches in length and are 
more or less single the result will give about 50 per cent rights and 50 per cent lefts. 
This condition exists at Hampton Roads. Out of 123 drilled valves from planted 
areas 67 per cent were rights — a result that is sufficiently close to be significant, since 
it would be quite natural to find, even under ideal conditions, more rights because the 
drills’ tendency to attack the thinner shells. 
The place of perforation on the shell depends on factors not yet determined. 
In the examination of this response one interesting fact became apparent. For these 
observations the area of the shell was divided into small squares and the perforations 
were correlated with them. Two important results were obtained: (1) Holes 
occurred on either shell and on every portion of them; and (2) 73 per cent of the per- 
forations were over or near the place of muscle attachment. The explanation for the 
latter is not evident, although it may be a thigmotactic reaction. 
Belding (1910) states that Urosalpinx cinerea requires from four to six days to 
drill through an adult scallop. Experiments (36 in all) made at Hampton Roads 
show that the average rate in oyster shells drilling is approximately 0.4 millimeter per 
day. Several factors such as hardness of shell, size of drill, and temperature modify 
this average. 
A study of the reactions of the oyster after perforation gave some insight into the 
method by which the drill lulls it. The first experiments made at Beaufort were as 
follows: The snail was permitted to drill through the shell of an oyster and then re- 
moved and the oyster observed. In every case the oyster eventually died from the 
perforation, proof that some toxic substance had been injected into it, since oysters 
which had been perforated with a common machinist’s twist-drill continued to live 
indefinitely. However, there were a few exceptions. If the hole was made by 
Urosalpinx so that only the edge of the mantle was perforated, immediate removal of 
the drill saved the oyster from death. On the other hand if its perforation was over 
the adductor muscle, the pericardial cavity, or the visceral mass, the oyster opened 
almost immediately, while if it occurred at the periphery it might be several days 
before the adductor muscle relaxed. After the oyster opens, crabs and other scaven- 
gers indulge in the feast, hastening the removal of the oyster, and causing the drill 
to attack new ones. From data collected at Beaufort one drill can kill from 30 to 200 
oysters in a season depending on their size. 
The drill like some other carnivorous gastropods feeds not only on live oysters, 
scallops, clams, etc., in the shell, but also on the meat taken from the shell — a fact 
significant for any method of control that plans to use the meats of these animals 
and of fishes as baits. Field and laboratory experiments were made in a study of 
this reaction, but only the latter gave usable results. The difficulty in the field was 
this: Owing to scavengers and putrefaction the bait did not last long enough to allow 
the drills to react to it, and although various types of cages were used to eliminate 
the scavengers it was impossible to keep the bait for longer than 12 hours (during 
the summer months, which is the time most favorable for trapping, because the drills 
are then most active), which was of insufficient duration. 
In the laboratory, experiments were devised to find out what meats the drill 
prefers and the maximum distance at which these are effective in attracting the snail. 
Completely satisfying results could not be obtained especially to the latter question, 
because the baits putrefied before the drill could get to them. The experiments were 
conducted in the following way: Meats of freshly killed oysters, clams, scallops, pin- 
