All About Rodents

Features - Rodent Control

May 19, 2016

Editor’s Note — Rodent Control: A Practical Guide for Pest Management Professionals is the definitive book on the biology, behavior and control of rodents in both urban and rural settings. Authored by renowned “rodentologist” Dr. Bobby Corrigan, the comprehensive 350-page book, available from the PCT Bookstore, covers a broad range of topics of interest to PMPs offering rodent control services, from “The Pest Significance of Commensal Rodents” and “Rodent Inspections” to “Challenging Rodent Control Situations” and “Rodent Exclusion.” In this month’s issue of PCT, we’re pleased to provide selected excerpts from this popular book, which are sure to pique the interest of our readers offering rodent control services.

Rats & City Alleyways

An attractive harborage and foraging site for rats.

There is often a mythical air about city alleyways and rats. Some people are afraid of alleyways, believing rats have become a natural inhabitant of these locations. Although this is not true, some city alleyways are prone to rat infestations, but only if humans allow it. The typical city alleyway by its specific “urban ecology” is an attractive harborage and/or foraging site for the Norway rat. Why is this the case? There are a number of reasons:

1. PROTECTIONS FROM PREDATORS. City alleyways tend to be long and narrow. Such a spatial arrangement allows rats to escape quickly to the safety of the walls on either side of the alleyway when they hear frightening sounds or detect the presence of a predator in the alleyway. In addition, alleyways are dark and quiet even during daylight hours. Rats are generally attracted to such shadowy locations to escape detection from their enemies.


Many foraging rats have a good chance of locating at least some food in a typical city alleyway. Many “back doors” of restaurants and apartments in inner-city areas open up to the alleyway, and thus these corridors are where trash cans, grease receptacles and Dumpsters are installed. Thus, food scraps and often piles of kitchen refuse in plastic bags commonly occur in alleyways. Wind-blown trash and food wrappers from the nearby streets often collect in the alleyway. If the alleyways are frequented by the homeless, they may leave trash and food scraps that are later used by rats.

3. EXCELLENT HARBORAGE. Many of the older alleyways in cities are in a state of disrepair. Deteriorating brick foundation walls and alleyway pavements provide ample opportunities for rats to hide or establish burrows. In addition, old furniture, equipment, pallets and other types of junk are often discarded into alleyways, providing daily cover or ideal long-term rat harborage. Alleyways also are often protected alcoves from cold winds and shaded against the direct hot sun during summer.

4. REDUCED CLEANING EFFORTS EXACERBATE THE PROBLEM. Because some alleyways may be or are perceived to be frequented by people involved in “shady” dealings (e.g., drug dealing, gang members, etc.), alleyways are often avoided by people. In these situations, trash may be dropped out of windows above the alleyway, creating a direct food source for the rats and/or the alleyway remains uncleaned by local residents and city employees concerned for their personal safety. Of course, not all city alleyways fit this profile. In well-managed areas, alleyways may be peaceful, clean and rat-free private “courtyards” that are thoroughly enjoyed by the residents. Again, management of the specific urban environment dictates any area’s vulnerability to pest populations.

Neophobic Rats or Departed Rats?

© Vitalii Hulai |

In well-established neighborhoods with abundant amounts of lush landscaping, palm trees and viney fence rows running along and connecting several backyards, roof rats sometimes enter and explore homes and commercial buildings in intermittent spurts. For example, rats living in the crowns of palm trees may venture down and enter beneath “closed” attached garage doors of several homes on a block to make “exploratory pass throughs” looking for food. Or roof rats from several properties away may visit a garage or an attic for an evening or two, leave behind some fecal pellets, and then not return to the residence or part of the street for several days or weeks, or they may never return.

Upon hearing the rats overhead or noticing rat scats, homeowners set out some traps or rat bait or call in a pest management professional. When the traps or baits are not interacted with, it may be wrongly concluded in these cases that a “neophobic” rat is living on the premises, but avoiding the traps and baits. Although in other cases that may be true, in these situations it is transient roof rats that came and went.

These events cause homeowners and pest professionals alike much frustration in chasing “ghost rats,” which may or may not visit the building again. Unfortunately, in neighborhoods where roof rats have abundant cover and food over several blocks, these events are common but unpredictable. The best strategy for residents in such areas is to rodent-proof their homes and buildings as thoroughly as possible and minimize leaving any attractive resources that may draw rats to the premises (e.g., spilled food, open garbage cans, etc.).