malajscy | AdobeStock

Buildings are constantly under siege during the warmer months of the year from various arthropods; they also are threatened by rodent invasion at any time of the year. More than 200 species of pests may invade buildings in the United States, most of which are incidental or occasional invaders.

Only a small percentage of pests invading buildings should be considered serious structural pests. For example, more than 70 species of ants invade buildings in the U.S., but only 10 or 12 species are considered major pests and in any given neighborhood, maybe 2 to 4 species are important.

German and brown banded cockroaches, Pharaoh ants, fleas, ticks, bed bugs and stored product pests largely rely on people or pets to transport them into buildings. All others originate from outside, which makes perimeter pest management of high importance in helping to keep homes and businesses relatively pest-free. This article will discuss some of the issues facing perimeter pest management and offer strategies for controlling peridomestic arthropod pests.

Perimeter treatments are but one tool in effective control of perimeter pests.
Stoy Hedges
Water damage is clearly visible at the base of these columns and proved to be the source of this home’s carpenter ant infestation.
Stoy Hedges

INCIDENTAL VS. OCCASIONAL. During my career in pest control, the term occasional invaders has been the standard for those pests that primarily live outdoors and invade from outside. Some, such as American and smokybrown cockroaches, silverfish, some spiders and camel crickets, can establish breeding populations indoors. The rest breed and live outside. In reality, only a handful of outdoor pests are true occasional invaders — meaning they live on the perimeter and regularly can be found inside. Examples include millipedes, centipedes, isopods, scorpions, crickets, earwigs and overwintering pests (lady beetles, boxelder bugs, stink bugs, etc.).

The rest of the insects and arthropods sometimes seen in structures are really what I call incidental pests. Examples include ornamental insects (e.g., thrips, psyllids, flying aphids); various bugs (e.g., wheel bugs, corsairs, burrowing bugs); spiders (orb weavers, funnel weavers, wolf and ground spiders); numerous light-attracted pests such as aquatic insects (mayflies, stoneflies, fishflies, caddisflies); leafhoppers; lacewings; and various beetles (e.g., ground beetles, may beetles). Incidental pests comprise the vast majority of the species sometimes found inside buildings. They typically do not live on a property, rather they are attracted there by outdoor lighting, by vegetation or by chance (spiderlings carried on the wind).

THE PERIMETER APPROACH. When a customer calls for service in controlling a pest problem, the inside pest presence must be addressed. In many cases (e.g., German cockroaches, bed bugs, stored product pests), most of the inspection and treatment will focus indoors. In others (e.g., carpenter, Pharaoh, odorous house and Argentine ants, smokybrown and American cockroaches, European earwigs, widow spiders, scorpions), focus may start indoors but needs to include outside as well. For the rest (e.g., filth fly species; woods, Surinam and Cuban cockroaches; most ants; aquatic insects; wolf spiders) the focus should be almost entirely outside. Even in the case of a home infested by German cockroaches, exterior inspection may reveal ants, spiders or other pests that may require attention before they can invade a structure.

A perimeter-oriented pest issue exists because conditions exist around the building that are (1) supporting the pest or (2) attracting the pest to the structure. A restaurant has house flies because the dumpster is dirty and/or too close to the building. A home has woods cockroaches because of the exterior lighting. Wolf spiders are more plentiful because of the thick ground-covering ivy next to the house. Web-building spiders are numerous due to the exterior lighting and the fact that the house has a pond or body of water nearby.

A pest professional should start evaluating a building while walking up to the structure (see photo left). Does the building have exterior lighting that attracts pests? How is the landscaping — thick ground covers, trees touching the building, flowering plants that could harbor aphids that are attractive to ants, piles of leaf litter? Are signs of moisture issues present — peeling or bubbling paint, gutters clogged (plants growing), leaves on roof?

Such evaluation should continue to all areas of the property. Are piles of items present (items that harbor ants, scorpions, cockroaches, earwigs)? Is firewood present and is it stored on the ground or next to the house (opportunities for cockroaches, earwigs, carpenter ants, termites)? Are many trees on the property and do they have tree holes (think cockroaches, earwigs, mosquitoes)? Are mulch layers thick on the ground in beds (ideal for millipedes, ants, isopods)? Are potted plants present (ants)?

In addition to conducive conditions, note potential entry points on the building. Does the house have weep holes? Are the vents (foundation, soffit and gable vents) properly screened? Do they have enough foundation or soffit vents? If not, then the attic or crawlspace likely will be more habitable for pests. Where are trash cans kept and are lids tight-fitting?

WHAT’S THE TARGET? A pest professional should always keep the type of target pest involved in mind. Where you might look to find the source for one pest differs for many others. If smokybrown cockroaches were involved, look at wood piles, tree holes, sheds, dog houses and piles of items. For Surinam cockroaches, check landscape beds and areas with heavy ground covers (e.g., ivy, pachysandra). If Cuban or woods cockroaches are the target, the type of lighting on the building needs to be addressed.

Customer education is important toward long-term relief from perimeter pests. Without customer commitment, more frequent insecticide applications are needed to maintain customer satisfaction.
Stoy Hedges

All pest ant species with the exception of Pharaoh ants originate outside, although satellite colonies inside are possible, especially with carpenter ants. Fire ants, big-headed ants and pavement ants nest in soil, including potted plants. Argentine ants, odorous house ants, crazy ants and others nest in soil, leaf litter, mulch and piles of items. Acrobat ants, carpenter ants and velvety tree ants almost always will nest in moist, dead wood. The Florida and Hawaiian carpenter ants nest in wood but also may be found under items lying on the ground such as lumber, cardboard and logs.

HABITAT MODIFICATION. The goal of a perimeter pest management program should be long-term relief from likely pest invaders from the outside focused mainly on the customer’s primary pest issue. Long-term reduction of pests beside a building can be achieved by changing or removing conditions that are or may contribute to pest infestations. Some such tasks are easy to complete while others take greater commitment from the customer.

Most habitat removal or modification efforts are the responsibility of the customer unless the pest professional feels qualified enough to offer a service to address specific needs (e.g., exclusion, installing gutter protection). Easy tasks involve changing exterior lighting to that which attracts fewer pests, cleaning up leaf litter, elimination of piles of items, storing firewood properly away from the building, keeping trash receptacles clean and located away from the structure, and regularly dumping water from items that collect rain and could breed mosquitoes.

Tasks a bit more difficult include some exclusion work, repairing leaks, removing leaf litter, cutting back tree limbs, redirecting irrigation heads away from the foundation, changing the type of landscape mulch or reducing its thickness, and filling in smaller tree holes with sand to prevent mosquito breeding. The most difficult tasks involve difficult exclusion installs (i.e., at roof returns, soffits and chimneys) and removal or changing landscape plantings. For example, a building regularly plagued by ant invasions may have many shrubs or trees that are aphid prone and should be changed out to plants that have few aphids. Changing out landscaping can be costly but can greatly reduce the numbers of ants on a property that might invade the structure. To pull out beds of thick ground covering vegetation is also labor intensive.

The pest professional should take the time to explain why certain tasks should be done to help alleviate a current perimeter pest issue and to reduce the future threat of invasion. Such communication should be noted in the service report — a task that is of great importance in commercial pest services.

Only a handful of outdoor pests (like this millipede) are true occasional invaders.
Stoy Hedges


TARGETED APPLICATIONS. Perimeter pest management should not primarily be focused on perimeter treatment to building walls and foundations. Most water-based residual insecticides have label restrictions that may prevent general surface treatments around many areas of a building. For example, any horizontal, impervious surface next to a building that could result in runoff to gutters, drains or bodies of water are restricted only to crack and crevice and spot treatments. Examples include concrete patios, driveways and sidewalks.

Pest professionals should keep in mind that residual treatments to exposed foundations, lawns and mulched areas may result in varying degrees of residual life for an insecticide deposit. Any environmental condition that reduces residual activity such as direct sunlight, rain or irrigation, or binding to soil or mulch, will require target pests to remain in contact much longer with the deposit to effect a lethal result.

Perimeter treatments are, however, a valuable tool as part of the overall perimeter pest management program but may prove to provide shorter-term results. Focus on reducing/eliminating contributing conditions and exclusion efforts is important for immediate and long-term relief from pests but is only as effective as the customer is willing to get involved.

In situations where a perimeter treatment may be helpful, it should be performed (i.e., many ant infestations). In cases involving overwintering pests (e.g., stink bugs, lady bugs), applications to the foundation are limited in effectiveness because these pests will be found mostly in the upper parts of a building. Crack and crevice treatments into pest entry points with a dust, aerosol or foam formulation are needed. Treatments to exposed surfaces around entry points, windows and doors may be restricted by label directions. For example, newer labels may restrict application to a surface band no wider than 1 inch around pest entry points. Other labels may allow 3- to 18-inch bands around windows or doorways. Applications to the underside of soffits often are allowed as general surface applications. Consult the product label before making applications.

More targeted treatments to sources of pest activity are needed to stop a current infestation in its tracks. Smokybrown cockroaches living in a wood pile or tree hole may best be treated using a granular bait product. Ant colonies in soil may be drenched with a water-based residual. Millipedes, isopods, earwigs and ants living in mulched beds may require raking back the mulch to expose the pests to more direct treatment. Severe ant infestations related to feeding on aphids in vegetation may require ornamental applications (which may require having an L&O applicator’s license) as would treatment of trees to control boxelder bugs or shrubs to alleviate an inside invasion of thrips or psyllids. Choice of the formulation and product to use will depend on the type of target pest and the location in which it is found.

SUMMARY. Perimeter pest management involves a number of factors from the target pest, where they are found and conditions contributing to their presence. Pest professionals should examine the whole property and take any conducive conditions into account to locate sources of the target pests (and other pests that may be present) and how such conditions may be manipulated to provide longer-term relief. Customer education and involvement is also important toward long-term relief from perimeter pests. Without customer commitment, more frequent insecticide applications are typically needed to maintain customer satisfaction.

The author is with Stoy Pest Consulting, Memphis, Tenn.