HOUSE FLIES. 7 
attain full size they gradually assume a creamy white color. Just 
before pupation they become very restless and migrate from their 
feeding ground in search of a favorable place in which to pass the 
pupal stage. They will often congregate at the edges of manure piles 
near the ground or burrow into the soil beneath, or they may crawl 
considerable distances away from the pile to pupate in the ground 
or in loose material under the edges of stones, boards, ete. 
The pupe (fig. 12), or “sleepers,” are more or less barrel shaped 
and dark brown in color. In midsummer this stage lasts from three 
to ten days, four to five days being the usual duration. The pupal 
stage is easily affected by temperature changes and may be prolonged 
Fic. 10.—Egegs of the house fly: Highly magnified. (From Newstead.) 
during hibernation for as long as four or five months. Numerous 
rearing experiments in various parts of the country have shown that 
the shortest time between the deposition of eggs and the emergence 
of the adult fly is eight days, and 10 and 12 day records were very 
common. 
The adult fly, upon emerging from the puparium, works its way 
upward through the soil or manure and upon reaching the air it 
crawls about while its wings expand and the body hardens and 
assumes its normal coloration. In a very few days the female is 
ready to deposit eggs. In recent experiments at Dallas, Tex., at 
New Orleans, La., and at Arlington, Va., it has been found that the 
