The Pest Ecology Of The Attached Garage

July 1, 2000

An attached garage is an attractive habitat to many different wandering animals so PCOs should pay close attention to these unique environments.

The word "ecology" is derived from the Greek word "oikos," meaning "home." The ecologist studies the interactions between organisms and their environments. Therefore, urban pest ecology can be thought of as the "home life" of the various different pest organisms that inhabit a particular type — or even part of an urban building or system.

Depending on where you live in the U.S., you learn through your inspections and work those animals that you are likely to encounter in your area, as well as within a specific part of a structure — such as crawl spaces, attics, a restaurant’s dishwasher room, a basement and so forth. In this article, we consider the pest ecology of a common, yet critical, area to homeowners and pest management professionals alike: the attached residential garage.

The Attached Garage. Although the sight of a garage may seem straightforward and simple, this scene is more complex biologically than what meets your eyes. Attached garages can be especially prone to pest invasions from several different arthropods and mammals. But why is this so? Let’s examine a few of the more important ecological factors involved in this unique area of our homes.

1. Ecological Equivalents. Depending on the time of the year, an attached garage can offer a wandering animal protection from its enemies, as well as from threatening climatic conditions such as cold, snow, dampness or heat. Essentially, a garage (or a similar space) can offer the ecological equivalents perhaps of a warm tree hollow, a cool cave, a burrow or some other type of natural protection. This factor alone is enough to lure some arthropods and mammals to venture into our buildings.

Some garages may also contain insulated attic storage spaces. These quiet and undisturbed spaces are attractive to raccoons, opossums, bats, roof rats, deer mice and birds. Additionally, if the ventilating louvers of these attic spaces are not maintained, various wasps and bees will take advantage of this ideal "tree hollow" in which to construct a nest.

2. A Naturally Conducive Structure. By its very design and function, a typical two- or three-car residential garage is conducive towards not only attracting pests, but also allowing pests easy entry. Several factors explain this.

First, although garage doors may be relatively tight when installed, rarely are they maintained in this manner by home-owners. Actually, most people do not know the difference between a door that is closed and a door that is closed and tight. Even when closed, the long garage door crevice typically allows for the escape of the attractive warm air currents (during cooler months) or cold air currents (during hot summer months). Food odors produced within a residence (discussed below) will also seep out of this crevice, providing yet another strong pest attraction.

Even if the garage door is kept pest tight, it is common for people seeking fresh air in their own "nests" during the spring and summer months to typically leave the garage doors fully or partially open most of the day and up until the time they go to bed at night. So pests are often permitted unimpeded entry to our homes directly. (Perhaps this is the same way pests used to enter the homes of early cavemen.)

Second, the dimensional plane of the attached garage’s floor is on the same level as the exterior space. Consider that most of the other doors on our homes and structures that accommodate human entry are elevated from several inches to several feet off the ground. These elevations provide a barrier to the causal or accidental entrances of insects and even some rodents.

Third, the two outside edges of the driveway ramp leading to the garage provides an excellent structural orientation guideline for animals. Many pests follow various structural lines to take a "path of least resistance" while foraging. This is especially true of ants, cockroaches and rodents, but is likely true of other animals as well. These driveway ramp edges form a pest highway extending all the way down to the street. Along the way, this by-pass intersects landscaped areas, mulch beds, turf and other exterior habitats that may be harboring arthropods and small mammals. Upon locating this structural guideline, pests can follow the line leading them to the food odors or to the cold or warm air streams. Some pests may even mark such areas with trail pheromones for the benefit of other colony members.

And fourth, most garages contain one or more entry lights positioned either above or flanking the car doors. Of course, these lights attract various flies, moths and a myriad of other flying insects to the garage door areas. Sometimes, bats, while following these flying insects, also fly into the garage and become trapped inside the home when the doors are put down for the night.

3. Attractive Odors. Sometimes, opportunistic insects and mammals randomly encounter a garage space during their forays. More often, however, they are likely to be drawn by food or attractive air currents. Several different types of food odors can leak from our homes. Leaking food odors during food preparation of breakfast, lunch and dinner are obvious. But urbanites often store large (10 to 50 pound) bags and containers of dog and cat food and various birdseed in their garages. Most times, these are stored directly on the floor (see photo above).

Pets are also frequently fed directly in the garages. Small spillage of pet foods and bird seeds in garages somehow don’t seem to be as important during house cleaning chores as those that occur within the rest of the house. Consequently, various foods accumulate within the corners and crevices of garages, attracting and feeding insects and mammals.

Another source of food odors comes from the trash. Garbage cans and bags typically contain meats, fish, fruits, vegetables, grains and empty (not really) food cans, bottles and wrappers. Trash is commonly maintained inside garages until collection day. This may be only once or twice a week (providing a busy homeowner remembers to put the trash out on trash day). Still, even after the trash is collected, the average trash receptacle, much like the food containers above, is not really "empty." Remaining, decaying old food residues and odors in the bottom of the trash cans provide a constant attraction and breeding medium to pests.

4. "Nested Nests." Once inside, pests discover that the garage provides a harborage within the harborage (i.e., "a nested nest"). We know as we service one home after another that sometimes garages become so cluttered that they no longer serve the homeowners as car garages, but merely as "big closets." Cardboard boxes and all types of junk fill in the wall and corners. Pests such as ants, scorpions, rodents, silverfish, spiders, cockroaches and others find the protection among the clutter highly favorable environments for breeding and proliferating undisturbed. Those garages that also contain food and sources of warmth via water heaters and furnaces provide the basic three elements of a good nest that is so essential for optimal growth and survival of offspring.

Opportunity Knocks. We can see how attached garages might provide opportunistic animals with valuable resources. But pest professionals can also be opportunists relative to offering quality routine services, as well as additional value-added services for residential garages. Here are some tips:

1. PCOs must be acutely aware of the importance of the ecology of the attached garage and its pest vulnerability. Good inspections and proactive thinking are always required in this unique room.

2. The installation of monitors provides for outstanding service. For those homes where the professional notices the storage of dry pet foods and/or bird foods, an excellent value-added service would be to also include monitoring traps, such as a pantry pest pheromone trap. Also keep in mind that various fruits, nuts or seeds are carried into and stored in garage attic areas by some animals, presenting yet another source of "pantry pests" to the home.

3. Pest proofing garage doors or replacing door sweeps is not typically on the "to-do" list of the average "weekend warrior." Moreover, most homeowners are not knowledgeable enough to do this correctly. This is a perfect opportunity for extra business!

4. It’s easy for a professional, while working inside a garage, to look outward with the door closed for a thin line of light leaking into the garage from the outside. If you see this, show it to the homeowner and explain the importance of pest proofing and resulting energy losses. Offer to pest proof the door and other areas for them.

Summary. Putting all of this together then, when we consider the relationship between a specific urban environment and the animals that utilize or adapt to that environment, we can better understand how to correctly and possibly even prevent pest problems from occurring in the first place. We should also always educate homeowners as to the importance of their role in maintaining the various residential spaces so as to not attract and encourage infestations.

By doing so, we practice IPM. But, you may find it interesting that before the term IPM was used, it was Professor Stephen A. Forbes, University of Illinois, who adopted the word "ecology" and stressed the importance of ecological principles when dealing with insect problems. When? In the 1880s!

The author is president of RMC Pest Management Consulting and can be reached at 765/939-2829 or

Further Reading and Materials

Begon, M., J. L. Harper and C.R. Townsend. 1986. Ecology: Individuals, Populations and Communities. Blackwell Scientific Publications. Sinauer Assoc. Sunderland, MA. 876 pp.

Corrigan, R.M. 1998. When conducting inspections, follow the lines. Pest Control Technology. GIE Publishing. Vol. 26 (12). pp. 66, 69.

Corrigan. R.M. 2000. Pests, pest control and your garage. Fact sheet for pest management professionals to distribute to homeowners regarding their role in managing their garages to prevent pest problems. Can be purchased via an e-mail note to:

Klotz, J. H. and B. L. Reid. 1992. The use of spatial cues for structural guidelines in Tapinoma sessile and Camponotus pennsylvanicus. J. Insect Behav. 5: 71-92.

Michelbacher, A.E. 1945. The importance of ecology in insect control. J. Econ. Entomol. 38: 129-130.