124
Life History of Musca Planiceps Weid
chorion unruptured, has been found in a speci-
men with fresh blood. A female released 10
hours from eclosion, and unfertilized, has been
recaptured 24 hours later with a blood meal
already partly digested, and with a larva fairly
advanced in development, (but still rather
soft and diffluent) and a mature egg. A speci-
men with a stage III larva was found with an
immature egg with no signs of embryonic deve-
lopment and only one more developing egg in
the follicles. It would thus appear that as
soon as a larva is born the uterus receives an
egg ready to hatch from one ovary whilst the
other ovary completes the development of the
next egg. The female genitalia are figured fig.
227, in Patton and Evans [1929].
The length of time spent by the larva in
utero is unknown. The larva lies head forward
in the uterus, but turns prior to birth. Mature
eggs removed from the mother and placed on
saline damped wool do not hatch.
Birth. On arrival the mother fly usually runs
about on the surface of the cow-dung mass for
about half a minute, examining it. She then
chooses for preference a depression in the
upper surface of the dung, otherwise the plane
upper surface is chosen, but the steep sides
of the slope of the pat are usually avoided.
Becoming motionless, the tip of the abdomen
is slightly depressed.
After a short but dis-
tinct pause, birth rapidly takes place.
The
'after birth', consisting of the chorion of the
egg and the moults of the first two instars,
intermingled, is attached to the posterior side
of the larva at about two-thirds of its length
from the head and is rubbed off as the larva
enters the dung, remaining on the surface as a
white speck. After birth the mother fly is not
usually easily disturbed for a few moments,
probably due to exhaustion, and may then fly
straight off, or stop and feed at the dung.
In nature delivery is almost always head
first, exceptions being usually under-sized
females, in which there is possibly no room for
the larva to turn. But when killed artificially,
a fair number of flies give birth tail-end first.
In neither case is the well-being of the larva
affected: if it occurs in nature the larva turns
straight over and burrows, if aborted by
maternal death the larva can equally burrow
immediately.
Larvae can live within a dead
mother,—if she is removed shortly after death
from the killing bottle—for up to 15 hours. A
fly found dead in a cage 14 hours after impri-
sonment was found on abdominal pressure to
contain an unturned larva, which on expres-
sion burrowed immediately. Another fly, killed
in the cage by a hunting spider was found next
morning to contain an active mature larva.
The anterior spiracles of the larva appear not
to be functional. A larva, half extruded, can
stand exposure to cyanide vapour for some-
time, but if the posterior spiracles are so ex-
posed for a moment, the burrowing powers are
affected.
Larval post partum development. The larva,
when born, is white, but when full grown, after
clearing the intestine prior to pupation, is clear
primrose yellow and rather elongate for a Musca.
The dung feeding period is normally about two
days, but on one occasion it was prolonged to
eight days. Pupation occurs in earth beneath
the dung.
Puparium. The freshly formed puparium is
white, passing within 24 hours through red to
dark brown, with pale segmental rings very
distinct, making it at once distinguishable from
those of other Musca species. The pupal period
is from 7-17 days, average 9-10.
Emergence. This usually takes place before
noon. In flies bred from dung which has been
exposed for 24 hours, emergence usually covers
three days, on the first of which only a few
females appear, on the second the main eclo-
sion of both sexes, and on the third day males
only. Often the small purely female emergence
of the first day is not seen, and the first eclo-
sions reveal both sexes. Almost always, how-
ever, there are some male emergences 24 hours
after the last female. At emergence the mal-
pighian tubules are deep yellow,—as is normal
in the male—and not pale as in later life.
Males over 100 hours from eclosion, and re-
captured 96 hours after release, still have the
testes paler and more translucent than in
captured wild specimens of unkown age.
Imaginal habits. Males have been found,
always in the morning, on flowers of Ocimum
sanctum. Only once has a resting male been
taken containing fresh blood. Again only once
has a male been seen on a bull, moving about
very restlessly, and was not seen to bite.
This last was the only occasion on which a
specimen of either sex has been seen on cattle.
Placed under netting on a calf, females have
refused to feed. But 56 per cent of all captured
females taken over six months contained blood
in the gut. Against the species being a night-
biter is that a few dissections done on flies
captured in the early morning have shown the
blood always in an advanced stage of digestion.
A specimen of blood submitted to the Impe-
rial Serologist proved to be bovine.