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The original item was published from 3/19/2021 10:51:00 AM to 4/17/2021 7:05:01 PM.

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Posted on: March 19, 2021

[ARCHIVED] Rats in Sewer




Like any other municipality, Marshalltown unfortunately has a few rats in their sewer system. Although we do not have a major infestation, you may experience an unwelcomed visit by one of these furry critters at one time. They live and breed in the sewer system because it provides an environment where they can thrive plus they are excellent swimmers. The main reason they will come into a house is that they seek food. Flushing food remnants from dish washing, garbage disposal use and other means provides a great trail for them to follow. Avoiding these practices will reduce the chance of someone seeing a rat. Other ways to prevent rat intrusion is to have your sewer line televised by a plumber to detect any defects that may allow a rat to surface. Safe use of pungent items like citronella, peppermint and eucalyptus oils, naphthalene or even bleach have been know to ward them off,   they do not like the scent of predatory animals like ferrets, dogs and cats. Making sure any sewer stubs or cleanouts are properly capped may also keep them from coming in and of course, keep your property cleaned up as to not provide hiding spots for them or any other nuisance animals. If you still have a rat that decides to share occupancy with you, you may call the City Sewer Division at 641-754-5749. We will ask you a few questions, attempt to verify your sewer location and then place poison baits in the proper manholes to attempt to get rid of them.



If rats would stay underground, they would be of little menace to anyone except sewer workers performing maintenance. Many municipalities with a large rat population have found that rats are born and bred in the sewers.  In these labyrinths, rats multiply so quickly, in fact, that they expand beyond the crowded conditions of the sewer and come above ground in search of food and shelter.

Rats also leave the sewers during flash floods, sewer construction projects and other conditions where there is an interruption in the food supply. "They seek shelter in private homes, garages and sheds.


Rats have no problem getting to the surface and finding their way into homes. They find breaks in brick and terra cotta sewer pipes (i.e., house drains or lateral lines) and tunnel to the surface. These breaks occur due to age, settling, wear and tear, tree roots breaking through, or during excavation.  Rats can burrow up through as much as eight feet of solid ground (Figure 1).

Once they get to the surface, rats find food under fruit trees, in gardens, flower beds, pet kennels and our homes. Once near the foundation, rats easily take advantage of dirt floors and any holes in concrete floors and stone walls. They can crawl up lateral house drains and enter homes through floor drains, roof drains, sewer vents and even toilet bowls (Figures 2 and 3).


Despite studying rats in sewers, little effort is used on a regular basis to control them. Municipal governments only get involved when sewer lines are being replaced or when there is specific evidence of rats in the sewer. For example, burrow holes between the street and sidewalk (Figure 1), holes around catch basins and man holes, or actual evidence of rats entering the basement via floor drains and fixtures.

One answer that has proven effective over the years is the use of pesticide bait mixtures molded into paraffin blocks. The blocks are mold and mildew resistant, convenient to handle, easily placed in the sewer, require no special containers and are large enough to reduce the cost of frequent inspections and replenishment. The anti-coagulant rodenticide that is used in the bait is safe to handle without polluting the water supply. It is also easy to secure and anchor in the sewer.

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