REPORT ON MOSQUITOES. 115 



streams were safe. The obvious conclusion is that if we dis- 

 pose of the surface water the mosquito problem is solved and, 

 in general, that is the gist of the recommendation made. But 

 as conditions differ for the various species it will be better to 

 treat them separately. 



THE SALT MARSH SPECIES. 



The home of these species is everywhere along the coast within 

 the influence of the marsh vegetation ; but especially on those soft 

 marshes of irregular surface just above the level of ordinary high 

 tides. In the depressions in these marshes water from extra 

 tides and from heavy rains, settles and remains long enough to 

 mature a brood. A marsh of this character is like a huge sponge 

 and becomes dry only under the influence of a long continued' 

 drought. Take out a sod in such a marsh and the hole fills with 

 water ; open a ditch and from thirty to sixty feet on each side all 

 the water held in the marsh will flow into it. Such ditches to be of 

 the greatest effect and most lasting, should be at least two feet 

 deep, while the width need not be greater than enough to hold the 

 ditch. In a marsh well covered with sod, with a mud bottom sev- 

 eral feet deep, a six-inch ditch is really better than a broader one, 

 because, by the shading of the banks, mosquitoes are repelled and 

 do not oviposit in it. Nor does vegetation start readily from 

 that low level and the ditches are therefore likely to remain 

 cleaner' than shallower ditches would be. The deeper the ditch 

 the more complete the drainage and the fvu'ther to each side the 

 influence will extend. Practically from two to two and one-half 

 feet deep and six inches wide at intervals of from sixty to one 

 hundred feet forms an excellent working formula for anv ordi- 

 narv marsh that is evenly infested. It has been indicated how- 

 ever that there is a comparatively low percentage of marsh area 

 that will require such treatment. 



Taking the infested marsh-land as a whole it is probable tliat 

 about eightv per cent, of it is amenable to this narrow ditching' 

 method, and these ditches, if undisturbed, will last for years with- 

 out attention. A very small percentage of the entire area will be 

 found too soft to maintain a narrow ditch and for these wider 

 channels must be dug, which will, in a year or two, so improve 

 the general character of the marsh that narrower ditches can be 

 used where necessary. A considerable area on the Barnegat Bay 

 shore has onlv a shallow sod covering over the sand and here 

 ditching is practically unavailable as a general method. Shal- 

 low ditches will help out individual cases and where there is an 



