CHAPTER III 



ENEMIES OF THE MOLLUSCA — MEANS OF DEFENCE — MIMICRY 

 AND PROTECTIVE COLORATION — PARASITIC MOLLUSCA — 

 COMMENSALISM — VARIATION 



Enemies of the MoUusca 



The juicy flesh and defenceless condition of many of the 

 Mollusca make them the favourite food and often the easy prey 

 of a host of enemies besides man. Gulls are especially partial to 

 bivalves, and may be noticed, in our large sandy bays at the 

 recess of the tide, busily devouring Tellina^ Mactra^ Mya^ Syn- 

 dosmya^ and Solen. On the Irish coast near Drogheda a herring 

 gull has been observed ^ to take a large mussel, fly up with it in 

 the air over some shingly ground and let it fall. On alighting 

 and finding that the shell was unbroken it again took it up and 

 repeated the process a number of times, flying higher and higher 

 with it until the shell was broken. Hooded crows, after many 

 unavailing attempts to break open mussels with their beak, have 

 been seen to behave in a similar way.^ Crows, vultures, and 

 aquatic birds carry thousands of mussels, etc., up to the top of 

 the mountains above Cape Town, where their empty shells lie 

 in enormous heaps about the cliffs.^ 



The common limpet is the favourite food of the oyster- 

 catcher, whose strong bill, with its flattened end, is admirably 

 calculated to dislodge the limpet from its seat on the rock. 

 When the limpet is young, the bird swallows shell and all, and 

 it has been calculated that a single flock of oyster-catchers, 

 frequenting a small Scotch loch, must consume hundreds of 



1 W. V. Legge, Zoologist, 1866, p. 190. 2 Blackwall, Researches, p. 139. 



3 Barrow, Travels in South Africa, ii. p. 67. 



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