8o8 



THE DIPTERA 



exhausted, and in captivity may soon die. The eggs vary in size 

 in different species from 0-15 to 0-5 millimetre in length. They 

 are elongate oval in shape, marked with longitudinal dark marks, 

 connected at places by means of cross lines. The eggs are laid 

 singly, and require four to six days in warm^ and fourteen days in 

 cold, weather before hatching. The larvae measure some 2 to 

 5 millimetres in length, and are composed of a head without eyes, 

 but with well-developed mouth-parts and .a Y-shaped mark, and 

 cylindrical body of twelve segments, each with a transverse row 

 of spinous hairs, and with spiracles on the first and penultimate 

 segments. The characteristic point about the larvae is the presence 

 of two very long bristles situate on two tubercles on the ultimate 

 segment. These bristles may be as long as the head and body 

 taken together. The length of the larval stages depends upon the 

 air temperature, and may last from two to fourteen days. 



The pupa, 2 to 5 millimetres in length, is motionless, lying in the 

 wrinkled, brownish larval skin which envelops its last three seg- 

 ments, and by which it is attached to the stone on which it lives. 

 The duration of the pupal stage varies from eight or nine to twenty- 

 eight days. The whole development, therefore, requires about one 

 month in warm and two months in cold weather. 



Habits. — These little flies are essentially nocturnal in their habits, 

 but are attracted by light. During the day they lie up in cool, 

 shady places in houses, etc., under bricks, in hollow trees, behind 

 shutters, books, pictures, etc., often in bathrooms, and more often 

 in latrines. They are very small, and can easily pass through the 

 meshes of an ordinary mosquito curtain and fill themselves with 

 human blood; or, failing this, they will content themselves with 

 animal blood — e.g., that of cattle, dogs, frogs, geckos, serpents, 

 lizards, etc. They fly quite silently, and only the female bites, 

 and that only at night. She appears to be stimulated in her biting 

 propensities by an increase of humidity and temperature, and will 

 even crawl under the bed-clothes to get at her victim. During the 

 act of biting the posterior end of the abdomen is raised, while the 

 whole abdomen becomes much distended with blood and reddish 

 in colour, except at the posterior tip. 



The originally replete female becomes half empty in sixteen, 

 and quite empty of blood in thirty-six to forty hours. When first 

 gorged, she cannot fly easily, and may be unable to escape from 

 the mosquito curtain, where she may be caught while quietly 

 digesting her enormous meal. During the day, as already stated, the 

 flies remain resting in cool, shady places in houses and other buildings, 

 under bricks, in hollow trees, behind shutters, pictures, books, etc., 

 and are often found in bathrooms, and more often in latrines. 



The larvae are very diflicult to find, because they are so small, 

 while the pupae are even more difficult to see, because not merely 

 are they small, but they are also of a colour similar to the stones 

 to which they are attached. Hence the habits of larvae and pupae 

 are not well known, and require to be restudied. Their presence 



