148 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



The locality in question is a small pond, the source of a small 

 stream. The pond has stony shores and was evidently formerly 

 of some depth. It is now bordered with woods and has been 

 extensively filled by leaves and mud. It is also at least half 

 overgrown with a layer of grass, interspersed with small bushes 

 of Myrica. The grass forms a dense carpet with its thick 

 root-stocks and dense vascular roots, through which, here and 

 there, appear small spaces of water with pond-lily leaves. The 

 whole layer is strong enough to support a man walking on it, 

 though it is very springy, and if one stands still, water appears 

 upon the surface and one sinks slowly. It was in the watery 

 spaces among this grass carpet that the egg-boats of Mansonia 

 perturbans were found, and to the roots below the larvse are 

 attached. It is essential for such a pond to remain in an undis- 

 turbed condition for it to make an ideal breeding place. Several 

 other ponds were seen with similar grass coating, but in most 

 of them the layers had been thickened by time and so densely 

 grown up with sphagnum or even bushes of considerable size 

 that breeding of this mosquito was no longer possible. A very 

 large swamp has been formed by the damming of a stream to 

 furnish power for an electric-light plant. At the upper end of 

 this swamp a large area, many acres, of this grass occurs, form- 

 ing an ideal breeding place, but, owing to the changes in the 

 level in the water brought about by its use in the electric-light 

 works, the proper conditions seem to have been destroyed. In 

 August the water was a foot below its normal level, so that 

 all the open spaces in the grass were dry and covered by a 

 hard crust. Oviposition at present is therefore impossible 

 here. However, it is not impossible that in a rainy season 

 (the present season is a dry one) this marsh might be perma- 

 nently flooded and breeding conditions reestablished. 



I am inclined to the view that practically all of the Mansonia 

 perturbans so troublesome to the inhabitants of Dublin came 

 from the small pond above described. Another pond with 

 typical conditions was shown me by Dr. Stowell, but it is so 

 small that no large numbers of perturbans are likely to be 

 produced from it. If this view is correct, the adult mosquitoes 

 must habitually fly at least 3 miles from their breeding place. 

 I do not regard this supposition as at all improbable. It is of 

 course possible that there are other breeding places in the vicin- 

 ity not at present discovered. In fact I expect that similar 

 ponds will be found in the more distant vicinity when the area 

 of exploration has been extended. 



As A remedy for the mosquito plague in Dublin, therefore, 



