(a) Sounds. Rodents can be heard scurrying about at night or during
the day when the part of the building that they inhabit is dark. Overhead scurrying is a
reasonably sure sign of roof rats.
(b) Burrows in the ground. Burrows may be found inside a building
with dirt floors, outside with the tunnel leading inside a building, around rubbish or
woodpiles, and around stacks of supplies stored outside. The presence of burrows is a
sign of Norway rats.
Holes. Rats gnaw holes to gain entrance for food and shelter.
(d) Smudges. Smudges along beams, pipes, or floors close to walls
indicate the presence of rat paths (runs).
(e) Droppings. Rats drop pellet-like excreta along the runs or on the
floor under the runs.
Tracks. Rat tracks are visible in dirt and insecticide dust.
(g) Dead rodents. In the absence of chemical and mechanical control
measures, dead rodents may indicate the presence of plague.
(2) Traps. While the evidences of infestations enumerated above are
important guides to making a survey, it is also desirable to set a number of traps in
order to collect specimens and confirm the results of the inspection. Live traps are
preferable to traps that kill the rodents. This permits submitting live specimens, along
with their ectoparasites, to an entomology laboratory for examination. A complete
rodent survey includes a survey of the ectoparasites (fleas, mites, ticks, and so forth)
that live on the particular rodent population.
b. Ectoparasite Control. The more serious rodent-borne diseases are
transmitted by arthropods rather than the rodents themselves. Therefore, it is very
important that measures be taken to prevent parasites on rodents that are trapped or
poisoned from leaving the dead animal and seeking a human host. Ectoparasite control
consists of applying an approved residual insecticide to all known rodent harborages
(shelters), burrows, runs, and similar areas. In addition, an insecticide dust should be
sprinkled around all traps and poison bait stations. Ectoparasite control should normally
precede rodent extermination operations by several days.
c. Rodent Extermination.
(1) Mechanical control. Mechanical control is achieved through the use of
traps. It is the method of choice in any area where food is handled or stored because of
the hazards created in using a poisonous chemical around food. A large number of
traps should be used since a 10-percent catch is considered good. Various types of