34 



Moore (1938) in his very thorough summary of this topic 

 cites the detailed description by Dewar (191 o) of the manner 

 in which the oyster-catcher (Haematopus ostralegus) opens the 

 shells of Thais lapillus and consumes the snails. It is presum- 

 ed that our western oyster-catcher {Haematopus bachmani) 

 may have similar habits, although no concrete evidence is at 

 hand. 



The white-winged scoter {Oidemia deglandi) frequents the 

 intertidal zone and feeds upon an omnivorous diet of mollusks 

 and crustaceans. On several occasions the writer has had an 

 opportunity to examine the stomach contents of these ducks 

 containing freshly fragmented shells of T lamellosa^ indica- 

 ting that they habitually prey upon the snails. 



Ravens {Corvus caurinus) are frequenters of the intertidal 

 zone, and with their omnivorous diet probably include Thais. 



Fishes of several species have been suggested as possible 

 predators upon Thais during the periods when their habitat is 

 covered with water, but there does not seem to be any well 

 defined proof of this relationship. 



Crabs are regarded by some observers as probable predators 

 on Thais^ but the evidence for this view is inconclusive, unless 

 we regard the angular fractures found on the shells as the 

 work of these animals rather than that of birds. 



Hermit crabs are commonly found occupying the shells of 

 the snails, but it is not believed they secure these by attack- 

 ing the living animals. 



A number of invertebrate animals become attached to or 

 burrow into the shells of the snails, but none of these appear 

 to be seriously detrimental to the Thais. The principal attach- 

 ing forms are barnacles, which often completely cover the en- 

 tire surface of the shell. The calcareous tubes of annelids and 

 colonies of bryozoans are not infrequent, but are usually seen 

 attached to snails inhabiting the lower tidal levels and reefs. 

 The most striking example of attaching organisms is to be 

 seen in areas where ths small Olympia oyster is cultivated; 

 here the microscopic larvae of the oyster settle upon the Thais 

 shell, and eventually develop into clusters, which as they ma- 

 ture must become an awkward burden to the snails. 



