146 



THE PLAGUE OF MUSSELS. 



ILYANASSA 

 OBSOLETA. 



is the tide-pools and weedy borders of rocky shallows, where barnacles, 

 hydroids, anemones, rock-loving limpets, and other associated forms that 

 find shelter among the algse, afford it abundant food. Though this is pre- 

 cisely where the mussels (Mytilus and Modiola) grow till the rocks are 

 almost black with them, it is said that they are never attacked by the 

 drills — an immunity to which, no doubt, is due their extreme 

 abundance in suitable situations. 



The urosalpinx sometimes strays of his own will away from 

 his native tide-rocks to the oyster-beds ; but usually he is saved 

 this trouble by being taken there with the small " seed " oys- 

 ters in course of transplanting to new ground. Finding plenty 

 of nourishment, he lives and increases rapidly enough to be- 

 come in the course of a. few years a very serious obstacle to the 

 planter's success by killing great numbers of the little oysters, for the old 

 ones, having thick, hard shells, are rarety bored. 



Once having attacked an oyster-bed, drills work with rapid- 

 ity, and seem to make sudden and combined forays at consid- 

 erable intervals. Their disappearance from certain restricted 

 localities, too, for a long time, is unexplained. Eels are said to 

 feed so greedily upon their eggs as almost to exterminate them 

 in some waters. 



Another serious cause of disquietude to the American oys- 

 ter-grower, especially in the Great South Bay of Long Island, is the fast- 

 ening of great quantities of young black mussels (Modiola 

 plicatuld) on the oyster-beds. This seems liable to occur also 

 in the lower part of the East River, and at Staten Island. 

 The mussels having established themselves grow rapidly, knit 

 the oysters together by their tough threads, making culling 

 very difficult, and take much of the food which otherwise 

 would help fatten the more valuable shell-fish. .On the Pa- 

 cific coast Gastrochcena, and various pholadiform mollusks are 

 a great bane to the oyster-reefs, which they penetrate by dig- 

 ging burrows wherein their whole shell is lodged. Large 

 numbers of these, with the help of boring-worms and sponges, may so rid- 

 dle a reef as to cause its entire disintegration. 



In Delaware Baj' the spawn of squids, in the shape of clusters of 

 egg-cases, appropriately called " sea-grapes," often gathers so thickly on 

 the oysters during the inaction of summer, that when the fall winds come, 

 or the beds are disturbed by a dredge, great quantities of oysters rise to 

 the surface, buoyed by the inflated " grapes," and are floated away. 



TBITIA 

 TRrVITATA. 



UROSALPINX 

 CINEREA. 



