The second method of handling manure is one which does not require the
application of chemicals. It is based on the fact, mentioned on page 4,
that the larvæ of the house fly, a few hours before they are ready to
pupate, show a strong tendency to migrate. This migration takes place
mostly at night, and the larvæ sometimes crawl considerable distances
from the manure pile. Now it is possible by means of a very simple
arrangement called a maggot trap to destroy fully 99 per cent of all
maggots breeding in a given lot of manure. A successful maggot trap
which the Maryland Agricultural College constructed at the college barn
is shown in Figure 9. The trap was designed by R. H. Hutchison and
constructed under his supervision. The manure, instead of being thrown
on the ground, is heaped carefully on a slatted platform, which stands
about 1 foot high. This particular platform measures 10 by 20 feet.
There are six 2 by 4 pieces running lengthwise 2 feet apart. Across
these are nailed 1-inch strips with 1/2 to 1 inch spaces between them.
The wooden platform stands on a concrete floor, and a rim or wall of
concrete 4 inches high surrounds the floor. The floor slopes a little
toward one corner from which a pipe leads to a small cistern near by.
This pipe is plugged with a stopper of soft wood, and the concrete floor
is filled with water to a depth of 1 inch in the shallowest part. Flies
will lay their eggs on the manure as usual, but the maggots, when they
have finished feeding and begin to migrate, crawl out of the manure,
drop into the water below, and are drowned. Each week the plug is
removed from the pipe, and all the maggots are washed into the cistern.
The floor is then cleaned of any solid particles by means of a
long-handled stable broom or by a strong stream of water from a hose.
The pipe being again plugged, the floor is again partly filled with
water and the trap is ready for another week's catch. A platform of this
size will hold the manure accumulating from four horses during the
period of four months, or about 20 days' accumulation from 25 horses, if
the heap is well built and made at least 5 feet high.
[Illustration: FIG. 9. A maggot trap for house-fly control. View showing
the concrete basin containing water in which larvæ are drowned, and the
wooden platform on which manure is heaped. (Hutchison.)]
Experience with this maggot trap clearly indicates that best results can
be secured if the manure is compactly heaped on the platform and kept
thoroughly moistened. It is best to apply a small amount of water each
morning after the stable cleanings have been added to the pile. It
should be borne in mind that in order to make this trap a success the
platform beneath the pile must be kept comparatively free of
accumulations of manure, and moisture applied regularly to drive the
maggots out.