18 THE STABLE FLY. 
REPRODUCTION. 
Mating of the flies takes place while they are not on hosts, and egg 
laying soon follows, provided the flies have fed a sufficient number 
of times. It seems that at least three feedings on blood are necessary 
for the production of eggs. After the third meal is digested the flies 
seek suitable places for deposition. When the weather is cool addi- 
tional feedings are often necessary before eggs are produced. The 
adults appear to have a keen sense of smell and are able to detect 
moist straw and suitable manure very quickly. This is especially 
noticeable when a straw stack which is dry on the outside is opened 
up so as to expose the moist and rotting interior. 
Very soon after a stack is opened flies are seen to come to the moist 
straw in numbers and begin depositing eggs. They usually crawl 
into the loose straw, sometimes going to a depth of several inches. 
When laying eggs the fly greatly extends the ovipositor and uses it as 
an organ of touch in locating a suitable spot in which to deposit. The 
eggs are laid in irregular masses, although occasionally single ones are 
deposited. The female usually moves several times during deposi- 
tion so that each mass contains from a few to as many as 25 or more 
eggs. The greatest number of eggs which has been observed to be 
deposited before another meal of blood is taken is 122. After all of 
the eggs have been deposited the female again seeks a host, and this 
feeding is again followed by deposition. Three of such depositions 
commonly take place in this species. It is sometimes necessary, 
especially during cool weather, for a fly to become engorged twice 
before each deposition following the first. The greatest number of 
eggs which has been seen to be deposited by a single female during 
her life is 278. 
LENGTH OF LIFE OF THE ADULT. 
A considerable number of experiments have been made to determine 
the length of life of the adult fly. A knowledge of the longevity of the 
adult is important in order that its possibilities as a pest may be 
determined and that we may ascertain whether the species may act 
as a true host of disease organisms; that is, whether disease germs 
can multiply within the fly before being capable of producing the 
disease in a higher animal. Individuals kept in small tubes without 
food or water during hot weather died within two days. When water 
and sugar sirup were supplied to flies, in a screen cage about 1 foot 
square, one specimen out of a large number of males and females lived 
for 23 days. Individuals which had access to blood at frequent inter- 
vals lived 17 days, and a few specimens, among a considerable number 
which were kept in large cages with cattle and suitable material in 
which to deposit eggs, lived for 29 days. When flies had been sup- 
plied with fruit and moist straw, but had not had access to host 
animals, they frequently lived for 10 days. 
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