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mosquitoes "which do not persecute man with the same persistence as certain other 

 species f. i. Aides calopus". Owing to the enormous masses of C. pipiens which must 

 every year be hatched from the incredible number of larva; which fill almost all 

 the ditches and pastures near our farms, there does not seem to be the slightest 

 accordance between the number which are hatched and the annoyance caused 

 by them. 



In 1919 an interesting paper by Prell (1919 p. 61) appeared. He has made 

 quite the same observation as I have. In 1917 there were plenty of C. pipiens round 

 Spa, but there was no mosquito plague at all. On the other hand, in Stuttgart, 

 where the mosquito plague is now severe, and as far as I can see also partly caus- 

 ed by C. pipiens, the plague was unknown before 1900. Prell correctly rejects 

 any attempt to refer "these peculiar facts either to different species" of C. pipiens 

 or to migration. He points out that C. pipiens like other and perhaps all Culex- 

 species has originally been a bird-mosquito; as it is an intermediate host for Pro- 

 teosoma which produces bird-malaria, this makes the supposition very reason- 

 able; even now in many localities it occurs as a bird mosquito. See also Howard, 

 Dyar and Knab (1912 p. 107), Lang (1920 p. 114). Its great power of living as 

 larva in polluted water has been a factor which altered its primary habits, accom- 

 modating it to the polluted water basins arising round human habitations. Still the 

 mosquito can keep its old customs of sucking blood on birds; its common appear- 

 ance in poultry houses makes this very probable. On the other hand its occur- 

 rence in human dwellings, more especially in stables, has now offered another 

 source from which it may satisfy its lust of blood, which is: domesticated mammalia 

 and man himself. The power and inclination in this direction is developed to different 

 degrees in the different countries and perhaps also in different years. I should be 

 inclined to think that in higher latitudes and at lower summer temperatures, the 

 old habits will be preserved. (See also Howlett 1910 p. 479). 



It seems as if the lust of blood in the Aedini, at all events of our Danish 

 species, is much greater than that of the genus Culex, Culiceila and Theobaldia. 

 American authors (Howard, Dyar and Knab 1912 p. 107) come to the same result. 

 From every part of Europe we hear of severe attacks now from one and now from 

 another species; 0. nif/ripes from the far north, O, communis, cantans, annulipes, 

 vexans, caspius have all a very bad reputation, everywhere attacking man or 

 large mammals; the landward migration of the salt marsh mosquitoes in search 

 of blood, the behaviour of the mosquitoes of the prairies, which are adjusted to fly 

 towards prominent objects, in that locality almost always large mammals or men, 

 point in the same direction. It need only be added, that the time of bloodsucking 

 in the life of the animals is really rather short. 



In our country the bloodsucking period for most species does not last more 

 than about three or four weeks; further it does not begin before two or three weeks 

 after hatching, a fact which I have observed in almost all these species (Exception Fin- 

 laya geniculata see pag. 102). It may further be pointed out as a phenomenon common 



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