_Aëdes calopus_, more commonly known as _Stegomyia fasciata_ or _Stegomyia calopus_ (fig. 134) is a moderate sized, rather strikingly marked mosquito. The general color is dark-brown or reddish-brown, but the thorax has a conspicuous broad, silvery-white curved line on each side, with two parallel median silvery lines. Between the latter there is a slender, broken line. The whole gives a lyre-shaped pattern to the thorax. The abdomen is dark with silvery-white basal bands and silvery white spots on each side of the abdominal segments. Legs black with rings of pure white at the base of the segments. Size of the female 3.3 to 5 mm.; male 3 to 4.5 mm. [Illustration: 134. The yellow fever mosquito (Aëdes calopus). (×7). After Howard.] It is preeminently a domesticated species, being found almost exclusively about the habitation of man. "Its long association with man is shown by many of its habits. It approaches stealthily from behind. It retreats upon the slightest alarm. The ankles and, when one is sitting at a table or desk, the underside of the hands and wrists are favorable points of attack. It attacks silently, whereas other mosquitoes have a piping or humming note. The warning sound has doubtless been suppressed in the evolutionary process of its adaptation to man. It is extremely wary. It hides whenever it can, concealing itself in garments, working into the pockets, and under the lapels of coats, and crawling up under the clothes to bite the legs. In houses, it will hide in dark corners, under picture moldings and behind the heads of old-fashioned bedsteads. It will enter closets and hide in the folds of garments."--Howard. It was claimed by the French Commission, and subsequently often stated in discussions of the relation of the mosquito to yellow fever that the mature _Aëdes calopus_ will bite only at night. If this were true it would be of the greatest importance in measures to avoid the disease. Unfortunately, the claim was illy founded and numerous workers have clearly established that the exact converse is more nearly true, this mosquito being pre-eminently a day species, feeding most actively in early morning, about sunrise, and late in the afternoon. On cloudy days it attacks at any time during the day. Thus there is peril in the doctrine that infected regions may be visited with perfect safety during the daytime and that measures to avoid the mosquito attack need be taken only at night. [Illustration: 135_a_. Aëdes calopus. Pupa. After Howard.] Dr. Finlay maintained that the adult, even when starved, would not bite when the temperature was below 23° C, but subsequent studies have shown that this statement needs modification. The French Commission, working at Rio de Janeiro, found that _Aëdes calopus_ would bite regularly at temperatures between 22° and 25° and that the optimum temperature was between 27° and 30° C, but their experiments led them to believe that it would bite in nature at a temperature as low as 17° C.