The Mosquitoes of New Jersey 



59 



and salinity (15 per cent or less), is the killifish. Where they are 

 present in considerable numbers no wrigglers are allowed to reach 

 maturity — all are eaten. Apparently these efficient natural enemies 

 are possessed of a desire to reach the edge of the marshes, for they 

 penetrate every creek and ditch not closed by blockage and are to 

 be seen at times making their way in shallow water among the grass 

 stems. 



Wherever the marsh-land is of such a nature that the high tides 

 cover it at frequent intervals no breeding occurs, the writer believes, 

 because the supply of "killies" is constantly renewed. 



Fig. 29. The ditch 10 inches wide and 30 inches deep has been adopted as the 

 best unit for open salt-marsh drainage. 



High-lying or shut-in meadows over which the tide rarely sweeps 

 are the breeders of salt-marsh mosquitoes. Even where an extra 

 high tide has stocked the holes with killies the water dries up and 

 the fish die ; the rain-water fills the holes, the larvae hatch and 

 mature, and a brood of mosquitoes gets on the wing. 



The problem of eradicating the salt-marsh mosquitoes is thus seen 

 to be one of determining just what parts of the marsh are breeders, 

 intervals or that which remains in deep depressions will be kept con- 

 stantly stocked with wriggler-eating fish. 



