210 MOSQUITOES OF NORTH AMERICA 



of Anopheles remained on the window screens from evening until the following 

 morning. 



Grassi found that Anopheles will bite even at night if the temperature is high. 

 He found them very troublesome on a calm night when the moon was shining 

 brightly. They proved very annoying up to 2 a. m., but after that the tempera- 

 ture fell and none were felt up to 4 a. m. ; between 4 and 6 a. m. they again bit 

 in the fiercest manner. The above observations apply to the hot plains of central 

 and southern Italy. In northern Italy the time during which Anopheles bites 

 is much restricted on account of the low night temperature. 



When it is windy no Anopheles are seen or felt. On calm evenings they come 

 in clouds and it may happen that on the next evening none appear. In suffi- 

 ciently shaded localities it is not rare to have Anopheles bite out of doors during 

 the day and this is also the case in houses which are not well lighted or when 

 the day is cloudy. Cases of Anopheles biting in sunlight are very rare. During 

 the day Anopheles, when hungry, will bite if a victim happens to be near, but 

 they will not go far to obtain food. 



Grassi further states that Anopheles do not come directly to artificial light, 

 but they are attracted to the edge of the illuminated zone. A method of getting 

 rid of the Anopheles and other mosquitoes in a room, indicated by Grassi, is 

 based upon their preference for a certain amount of light. In the evening the 

 room is closed and the light allowed to enter only through a single aperture; 

 the mosquitoes will then leave by this opening. This expedient is only successful 

 at twilight ; during full daylight the mosquitoes can not be induced to leave in 

 this manner. 



Careful observations in Brazil, by Doctors Chagas and Neiva, show that the 

 different species of Anopheles follow each other in regular sequence in the 

 evening and morning twilight. Thus ISTeiva found that, at Xerem, Anopheles 

 pseudomaculijjes appeared first, later Anopheles intermedium, and last, when it 

 is already quite dark. Anopheles mediopunctatum. Anopheles alhimanus and 

 argyritarsis appear together as soon as the twilight begins and remain until 

 dark. Apparently the activity of each species is governed by a definite amount 

 of light and on this account the time of appearance and disappearance of a 

 species varies with the season and with the weather conditions. Generally the 

 time for biting lasted but thirty minutes but this was extended on moonlight 

 nights. These observers found that with artificial light the Anopheles bite at 

 all hours of the night but they doubt that they bite in absolute darkness. In the 

 morning the Anopheles appear when it is already much lighter and remain 

 longer, but they appear in much smaller numbers. In the forest every species of 

 Anopheles comes to bite during the daytime but not in such numbers as in the 

 evening. Dr. Neiva found that Anopheles hrasiliensis attacked man and animals 

 in open fields in the hot sunshine, and immediately after a rain it appeared in 

 true swarms, characteristic for this species. 



Anopheles crucians, according to Smith, bites during the day, and the same 

 authority has upon rare occasions seen Anopheles punctipennis bite in the after- 

 noon on porches in New Jersey. One of us (Knab) has been attacked by this 



