The Mosquitoes of New Jersey 63 



these large pieces are heavy, not easily moved by the tide, and can 

 be conveniently carted away by the landowners. 



In every area ditched thus far, small shallow pools have been 

 found which do not drain readily into the neighboring ditches and 

 which are too small to merit drainage by means of a spur. Such 

 holes are filled with sods from the ditches. In a couple of years the 

 grass grows over the fill, obliterating the hole. After the sod filling 

 has been thrown in, the surface of the rough pile is broken up and 

 smoothed off. 



The last few years have witnessed some very important changes 

 in the methods employed in trenching the salt marsh for mosquito- 

 control purposes. 



It has been clearly shown during that period that no salt marsh 

 is so well drained that it will at all times be free from mosquito 

 breeding. There are times when, because of high tides, continued 

 rain, and cloudy weather (during which the rate of evaporation is 

 greatly lowered), the water derived from high tide or heavy rainfall 

 or from both fails to be drawn off in time to prevent the maturing 

 of the last remnant of the brood. Moreover, it may be said that 

 the ditch mouths become plugged with sand or seaweed through the 

 action of the waves and that by one means or another the ditches 

 farther up in their courses become plugged with pieces of sod, 

 accumulations of hay, and other rubbish. 



It can be said, however, that during the past five years no case 

 has come to the author's knowledge in which the 10 by 30-inch 

 trenching of the ordinary high-lying salt marsh has failed to elim- 

 inate all but a small percentage of the brood which started. 



The apparent inability of the ditching to afford complete control 

 of breeding has demonstrated the maintenance of a patrol of the 

 drained salt marshes throughout the mosquito-breeding season, as 

 one of. the measures necessary to successful mosquito-control work. 



The greatest differences of opinion relative to the amount of 

 trenching necessary to free an acre of breeding salt marsh from dan- 

 ger have existed, and to a considerable extent still exist. An attempt 

 to discover the cause for this difference quickly reveals that each 

 opinion is based on the particular area or areas of salt marsh with 

 which the persons expressing them have had to deal. 



Some marshes, because of a larger percentage of the area being 

 filled with holes and depressions in which the high tide or rain- 

 water is retained, require more extensive drainage than others. 

 Furthermore, some marshes are protected from the tide by dikes 



