262 MOSQUITOES OF NORTH AMERICA 



nacity of this mosquito in returning to its victim after it has been repeatedly 

 driven off is almost characteristic. It has been noted repeatedly by us that 

 females escaping while being transferred from one jar to another would almost 

 unfailingly return after a few minutes and attempt to secure food from one of 

 us. On one occasion a marked female was driven off five times during one fore- 

 noon ; once she remained away nearly an hour, when her intended victim becom- 

 ing tired of further timekeeping, finally recaptured her. Having satisfied its 

 desire for food it gives vent to a triumphant note and goes in search of a resting 

 place." 



The French investigators determined that calopus would only drink blood that 

 it could itself extract from the body. When females were placed upon a patient 

 who was wet with a hsemorrhage from the mouth they refused to feed upon this 

 blood and in case the mosquito was hungry it sought a place that was not daubed 

 with blood and fed by piercing the skin. When given the choice of cold blood 

 and sweet substances they preferred the latter. Otto and Neumann were able to 

 feed female calopus on a mixture of blood and salt solution ; the French investi- 

 gators think that this must have been done under very favorable conditions and 

 that it does not invalidate their own observations. 



TIME OF ACTIVITY. 



The yellow-fever mosquito in the West Indies is known often as " the day 

 mosquito." It is usually active and bites only during the daytime, although 

 where there is a light in the room it may also bite at night. Finlay, in his paper 

 of 1881, already called attention to the strictly diurnal habits of this species and 

 contrasted it with the exclusively nocturnal habits of the other house mosquito 

 of Havana, Culex quinquefasciatus. He thought that there must be a constitu- 

 tional difference in the two mosquitoes which accounted for the different habits 

 and this he concluded to be the greater resistance of calopus to heat. He placed 

 females of the two species in glass tubes and exposed them at midday to the 

 direct rays of the sun under identical conditions, the thermometer marking 

 42.25° centigrade, the relative humidity 31.75. The Culex died after five 

 minutes while the calopus remained unharmed after 15 minutes and continued 

 alive in its tube through a further 24 hours. 



Working Party No. 1 of the U. S. Public Health and Marine-Hospital Service, 

 at Vera Cruz in 1902, found that the greatest activity of this mosquito is during 

 the dajrtime. They also observed them feeding upon members of the party at 

 night by artificial light. They found them to be especially voracious early in the 

 morning, about sunrise, and again late in the afternoon. Durham, in Ms studies 

 at Para, Brazil, was also struck with the diurnal habits of calopus and calls it 

 " solely a day gnat." 



" It is on the wing and will bite shortly after sunrise (about six a. m.) ; again, 

 a few have been observed biting about eight to nine a. m., after which there is a 

 pause till about eleven a. m., when again a few may be feeding. The time of 

 chief activity is in the middle of the day, from about twelve to two p. m., they 

 then bite freely, and are seen to copulate on the wing in numbers ; another pause 

 follows, though there may be a few about, but they do not cause trouble when 

 one is sitting at the microscope until about half -past three till about five p. m. 



