3-5.
MECHANICAL CONTROL
a. Trapping. The use of traps is largely restricted to survey work; however,
under certain circumstances, traps may be used as a method of control. Trapping is
recommended for use in those places where it is not advisable to use poison bait or
gas. It is also recommended as a follow-up to rodent poisoning to kill any rodents that
survive. It is a slow method of reducing populations and it is normally reserved for smell
rodent populations. Generally, less than 10 percent of the traps can be counted on to
effect satisfactory rodent control. The need for using a large number of traps in all
promising locations is therefore evident.
(1) In trapping rats, the proper placement of the trap is far more important
than is the selection of a bait. As previously stated, rats follow natural runways
whenever possible. Their instinct for security and protection causes them to travel
behind anything that is placed near a wall. The best baited trap will rarely entice a rat
into the open. When a trap can be set behind objects that are stacked close to the wall
or behind a board leaned against a wall, it will be much more likely to lure a rat into
investigating it. Live trapping is used to obtain specimens of infected animals in a
plague situation and should begin at the center of the infested area and move outward
in a radical direction as far as the animals are found. The snap trap is the one of
choice, after you have determined that there are no diseases present in the rodent
population. Steel traps with approximately 3 1/2-inch jaw spread (size No. 0) are also
used (see figure 3-1). Cage and box-type traps are sometimes used when live,
Figure 3-1. Three frequently used rat traps. (A, wood-base
snap trap, with bait; B, steel trap, used baited or
unbaited; C, snap trap with expanded trigger).
MD0172
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