150 MOSQUITOES OF NORTH AMERICA 



time by overflowing sea-water from a high tide or storm, at another by the flood- 

 ing from heavy rains. On the Panama coast the larvae of a species of Stego- 

 conops and of Aedes fluviatilis occur in rock pools of concentrated sea water 

 resulting from the splash of high seas. The larv^je of these identical species occur 

 inland in perfectly fresh water. Of most of the salt-water species it may hov/- 

 ever be said that they adhere closely to the tide-water region; Aedes sollicitans 

 may almost be said to be confined to the pools immediately back of the sea 

 beaches. While these larvse occur in salt or fresh water and will survive a cer- 

 tain change of density of their medium, as in the case of a salt-water pool being 

 diluted by rains, transfer from one medium to the other is fatal to them. The 

 cause of death in this case is the osmotic action of the media of different density. 

 Perhaps the most remarkable of the species breeding in salt water is Aedes 

 zamniittvi of the Mediterranean region. According to Surgeon E. H. Ross 

 they occur only in highly concentrated sea-water as it occurs in the rock-pools 

 left by high tides. He states that while, in summer Mediterranean sea-water 

 contains twenty-eight grammes of salt per litre, this species "can only ]ive in 

 water containing from forty-eight to eighty-seven grammes per litre of salt. 

 As soon as salt begins to be formed on' the surface of the pool, the larvae and 

 pupas move on to another part of the pool, which is often most extensive. These 

 pools may be very deep, but, in common with all the sea-water pools on the shore 

 of the Mediterranean, never contain fish or shrimps. When a thin layer of salt 

 forms on the whole surface of the pool, the larvae die." Carter found that if the 

 water was sufficiently saline the larvae were present, regardless whether the 

 water was strongly polluted or very clean. At Port Said he found them in 

 cesspools under the houses in which there was a large percentage of salt. 



THE FOOD OF MOSQUITO LARV/E. 



The larv£e of many species undoubtedly swallow anything in the water that 

 they inhabit which can enter their mouths. With many of the species the mouth- 

 brushes produce a vortex into which pass all minute objects floating on the water 

 or suspended in the water. The spores of algag, particles of dust, bacteria, pro- 

 tozoa, minute aquatic animals of miany different kinds, are thus swallowed. With 

 many species it seems that the important food is animal. Anopheles has been 

 found feeding upon the dead bodies of other culicid larvge. In studying the 

 larvae of Anopheles quadrimacuJatus in the laboratory, these insects seemed to 

 thrive best in water containing green algae, and this observation has been con- 

 firmed by other laboratory workers ; but it has been suggested that perhaps the 

 important food of these larvae is after all the microscopic animal life which 

 swarms among these alga and of which the algae themselves constitute perhaps 

 part of the food. The alg^ in our experiments belonged to the genera Aedo- 

 gonium, Cladophora, Spirogyra and in lesser degree Oscillaria. Stephens and 

 Christophers have found that the food of Anopheles larvae examined at Accra 

 consisted of a unicellular organism (Protococcus?). Theobald found that the 

 food sucked into the mouth of the larvae of Culex pipicns and C. nigritulus 

 consisted of algse and water Crustacea such as Daphnia and Cyclops. He has 



