368 
Parasites of Common Flies 
male emerged from the puparium. Consequently it was useless for the female 
to wait for the male to emerge as happens according to Malyshev (1913) when 
the parasite infests certain wasp larvae. 
In eight instances the first puparia were removed, and a male together 
with fresh fly puparia added, the additions being made between the seventh 
and eighty-second days. In four cases (Nos. 4, 9, 10, 11) females, which as 
virgins produced males, were employed. No further parasites were produced in 
two of these experiments (Nos. 4, 11), but in the other two a few more of the 
parasites developed in 3 out of 5 and 2 out of the 6 puparia used. The five 
infested puparia contained 3 $ and 16 $, 6 d and 14 $, 1 $ and 19 $, Id and 
6 $ and 1 d and 6 $ respectively. In four cases females (Nos. 8, 12, 17, 18), 
which as virgins produced no males, were employed. Not a single parasite 
was found in the 24 puparia used. 
One of the females lived 95 days, 14 lived more than 40 days. The mean 
length of life was 35 days. 
In another experiment carried out in 1917 a remarkable number of males 
developed. Seven unfertilised females were given six fresh fly puparia. In 
two of these 6 d were found, in one 4 d, and in one 2d, a mean of 4-5 d for 
each infected puparium. 
Howard and Fiske (1912, p. 209) were greatly troubled with M. acasta in 
some of their experiments with tachinids, and report some interesting observa¬ 
tions. Its chief characters are “ extreme hardiness and an insidious inquisitive¬ 
ness, which seems to know no bounds.” These parasites attacked several 
different kinds of fly puparia as well as hymenopterous cocoons. “They will 
enter the damp earth to a depth of several inches in quest of puparia, which 
have been buried therein.” “The eggs are deposited upon the surface of the 
nymph in an irregular circle surrounding the wound made by the ovipositor. 
They are very small and appear to swell somewhat before hatching, and if the 
puparium is broken open so that they are freely exposed to the air, they will 
fail to hatch.” They noted that the male emerged first and state that “they 
are invariably in the great minority and their numerical strength is still 
further reduced by the terrific duels which follow their emergence. Notwith¬ 
standing their physical defects in the matter of sight and powers of flight, 
their seeming weakness otherwise and their small size, even when compared 
with their mates, they possess a courage and vigour which is most surprising. 
In the instance of a colony which had been removed, from the puparium in 
which it was reared through its early stages, to a small glass cell, the several 
males which issued well in advance of the females engaged forthwith in 
conflict, in the course of which a considerable number were killed. The 
survivors of this Lilliputian battle royal calmly awaited the issuance of the 
members of their harems and proceeded to mate with one and all with an 
ardour which seemed to know no limit.” 
“The females (virgin) positively refused to deposit more eggs than would 
have normally produced males had they been properly fertilised. Instead of 
