one's index finger, is tied securely to the trigger. Ground baits may be used but are
difficult to fasten properly. Baits may be of any food (listed in the section on poisons)
attractive to the rats. The baited traps should be placed near, but not in, rat runs
because rats prefer to investigate food and may be wary of obstructions in their
runways. Traps near a wall or other vertical surface should be placed about 1 foot from
and at right angles to the wall, with the hair trigger toward the wall. Therefore, a rat
running along the wall from either direction, in leaving the run, will go straight for the bait
on the trigger. Camouflaging traps by sprinkling dust or other light material over all but
the bait is desirable, but care should be taken to prevent interference with trigger or
spring action. On earth floors, the base of the trap should be worked down into the soil
until the top is flush with the ground level. Sufficient headroom for the trap to spring
should always be allowed. Baited traps are best trap set in runway. Fastened down, so
that a rat caught by the tail or foot cannot drag them away, but this will not always be
required. Baits should be changed at least every third day unless a permanent-type bait
or a bait with a preservative is used. Rancid bacon or moldy cake usually will not tempt
a rat. It is also desirable to vary the bait every few days, switching to an entirely
different type. If a bait is eaten from the trigger without springing the trap, the setting is
improper or the trap is defective; however, baits sometimes are eaten by mice or
insects. Snap traps may be used unbaited if the trigger is enlarged to provide a pattern
on which rats may step (figure 3-2). This can be done by fastening a 1 1/2-inch square
of fly screen, tin, or cardboard securely to the trap trigger or bait hook. Fly screen, or tin
may be soldered to the trigger, or cardboard may be wired in place. Traps so modified
are termed expanded-trigger traps or flap traps and must be placed directly in rat runs
since there is no lure. Boards, boxes, or other obstacles should be placed beside or
immediately behind such traps. Placing of these traps requires knowledge of rat habits;
the trigger must know exactly where the rats travel if he is to catch them. The traps may
need to be camouflaged for any wise rats that survive after the first few days of
trapping. In addition to the usual settings for expanded-trigger traps in rat runs and
corners, near burrows, and holes, and in protected secluded areas, they also may be
placed on shelves, tops of fixtures, beams, pipes, and other overhead runways. On
overhead beams, particularly for roof rats or mice, wood traps can be suspended either
horizontally or vertically on the beam, with the trigger in the rodent's normal path. A 1/8-
inch hole may be drilled 1/2 inch from the front center of the trap, a small finishing nail
driven into the beam at the point of the setting, and the trap hooked over this nail. A
string from the back of the trap is tied to a nail in the beam below. Thus, when a rat is
caught, the trap is jarred off the nail, and the rat and the trap hang down by the string.
(3) Steel animal traps usually are not used with bait on the trigger, and only
an occasional rat is caught by the neck. Steel traps catch rats by the leg or belly. They
require careful adjustment, even when new. Any burr of metal on the trigger catch or
release lever, which would keep these parts from slipping easily, should be filed off.
When properly adjusted and set, the tops of the two jaws and the trigger pan should be
in one horizontal plane (see figure 3-3). The height of the jaws is regulated by turning
the spring in a counter-clockwise direction. In an adjusted trap, the spring arm will be
approximately 45 degrees from the axis of the jaws, and one jaw will fit into a small
depression in the spring handle. Each steel trap is provided with for a chain and a ring.
MD0172
3-6