INTRODUCTION . 21 
often particularly true in Army posts, camps, or stations where 
every attempt is made to keep the reservation sanitary but 
where flies are being attracted from outside sources. There are 
several methods for reducing the abundance of blowflies. The 
treatment of outside walls and surfaces, particularly garbage 
areas, transfer points and street gutters with a 2.5-percent DDT 
in a wettable powder spray preparation at 15 to 30 day intervals 
is highly desirable. 
Blowfly traps. Fly traps are of some value in catching blow- 
flies that are attracted to clean, sanitary areas from outside 
sources or the few flies that always escape even the most thorough 
methods adopted for their destruction. Traps are of no primary 
value in the control of flies. 
Although many different models and types of traps have been 
devised, most of them operate on similar principles. Blowflies are 
positively phototropie and they usually fly toward a light upon 
entering a darkened area. The principle upon which all success- 
ful blowfly traps operate is to induce flies to enter a bait chamber 
by means of an attrahent. They then fly upward toward light 
through a passage with a large opening and a small exit into a 
eage from which there is little opportunity to escape. As a result 
of extensive experimentation, it has been found by F. C. Bishopp 
and E. W. Laake, that the most effective, economical, and easily 
operated of all fly traps is the conical type recommended in 
United States Department of Agriculture Farmers’ Bulletin 734 
(rev. 1937), pp. 3-5 and fig. 1. Most other traps based upon the 
bait-light principle catch only a minor fraction as many flies as 
are caught in this trap. 
Blowflies are attracted in greatest numbers to decaying meats 
or meat products. Odors from such baits are obnoxious and may 
not be desirable about dwellings or stores. Usually the stronger 
the odor of the bait, the greater the drawing power. The larger 
the bait, the more blowflies it will usually attract to a trap, and, 
other things being equal, small quantities of rotting meat attract 
only small numbers of blowflies. When the bait has reached a 
certain stage in its decay its value as an attrahent is gradually 
lost, and new bait must be prepared. A bait which is exception- 
ally effective for blowflies is composed of the mucous membranes 
that form the intestinal linings of hogs and cattle. This sub- 
stance, called ‘‘gutslime,’’ is obtainable from packing establish- 
ments where sausage casings are prepared. Meat of any kind, or 
entire carcasses of small animals with the intestines exposed, will 
make satisfactory baits. It is best to place such decaying meat 
in water in the bait pans during warm, dry weather. Some mag: 
