[Ant Control Issue] The Old and the New

Management strategies for carpenter ants are almost as diverse as the types of structures where carpenter ant infestations occur. These strategies incorporate many of the older techniques coupled with newer chemistries and formulations. Baiting, for example, has been used for more than 70 years but the knowledge that not all ants will respond to the same bait is now more fully understood. It is important to have a bait that can be transferred to other members of the colony. Dead ants at the bait station may be viewed favorably by homeowners but they are not satisfied when the numbers of ants have not decreased in the weeks or months after baiting. Toxicants in bait must be low enough not to be detected or repelled by the ants and must be transferable to the majority of nest mates and brood in the colony.

The season may dictate what type of bait to use. In late winter and early spring, ants are often discovered by homeowners in bathroom or kitchen areas where ants are attracted to water. A water-based bait works better at this time of year than later when ants are foraging for insects on the exterior.

Perimeter sprays in the past had little residual activity. The toxicants killed the ants on contact and the resulting dead ants were viewed favorably by homeowners. The results were usually short lived as the chemical broke down in a few days and other members of the colony resumed activity. Older chemistries were also detected by foraging ants and foraging trails were shifted to avoid treated areas. Many of the newer chemistries are not detected by foraging ants. Some chemicals have a quick-knock down and foragers are killed as they come into contact with the chemical. Others have a delayed activity which allows the foragers to transfer chemical to the remainder of the colony.

Formulations have also changed and the challenge of placing the wettable powder into a spray tank or dealing with the effects of emulsifiers is gone. Formulations such as SC are easier to handle and measure, which provide additional safety for technicians.

In the past, carpenter ant control in a home required a "clean-out" followed by follow-up treatments to prevent a re-infestation. This involved drilling into wall voids to add chemical, treating attic and crawl spaces, applying perimeter sprays on the exterior and the sill plates. Attempts were made to locate parent colonies and all satellite colonies to prevent callbacks. Treatments were expensive in terms of the amount of time spent by technicians and the cost of chemicals.

With the variety of chemicals and application methods available today, a more diverse menu of management strategies can be offered to the homeowner. This is particularly appropriate with an understanding of the biology of carpenter ants involved in the infestation. First, the season will determine activity patterns of the ants. Infestations in structures should be treated differently in winter months than in spring and summer months.

In winter months, in homes with central heating, carpenter ants may emerge or make their first appearance during these cold months. Their metabolism is low and they are not foraging for food. These ants are found around water sources, such as in bathrooms and kitchens. Also with heating, winged carpenter ants, particularly males, that are over wintering in satellite nests, emerge several months before their counterparts living in the natural environment. Workers may feed on a water-based bait; males will not feed.

An inspection to locate satellite nests should be made. Nests occur under attic insulation, above subfloor insulation, in wall voids or in other hollow spaces within the structure. If several nests occur within the structure or when the nests cannot be located, it may be necessary to drill into wall voids to inject chemical. An exterior perimeter spray is not recommended when ants are not foraging.

Different approaches to management are made in spring and summer months when carpenter ant activity peaks. During the foraging season for carpenter ants, management tools include the use of toxic baits and perimeter sprays. Baits are placed where ants are foraging on the exterior of structures. Perimeter sprays that are non-repellent are placed where ants trail on the treated surfaces. Ants will transfer low-level toxicants to other members of the colonies. More toxic perimeter sprays will eliminate carpenter ants as they leave or enter structures but may not be transferred. These chemicals are most effective in controlling a new infestation.

To protect chemicals from environmental degradation, they should be placed in areas not exposed to direct sunlight and rainfall, such as under the lower edges of siding, around decks and under window frames where ants frequently travel and enter structures.

Foraging trails should also be located and treated. Since less then 10 percent of the colony population is foragers, it is important to select a chemical that has residual activity or one that can be readily transferred to other colony members. Foragers will not continue to leave a colony after a certain percentage of workers has been eliminated. A specific number, so far undetermined, will remain in the colony and survive until another season.

CARPENTER ANT INFESTATIONS. Are all carpenter ant infestations the same? Do all homes have the same potential for carpenter ant infestation?

Carpenter ants infestations are different for a number of reasons. First, there are many species of carpenter ants that cause structural damage and many species that are nuisance pests. Whereas Camponotus modoc, C. vicinus and C. essigi are major pests in western states, C. pennsylvanicus, C. noveboracensis and C. nearcticus are major pests in middle and eastern states and C. floridanus is important in the Southeast. A total of 24 species have been identified as occurring in structures in the United and Canada either as structurally damaging or nuisance pests. Each species has differences in behavior, morphology and physiology, but all nest in wood. Many infestations are identified and managed before significant damage occurs in structures due to observations and inspections of homeowners and pest management professionals.

Structures are different in size, construction, location, age and maintenance. Wood used in framing, siding, roofing, floors, decking and decoration plus insulation are all potential nesting sites for carpenter ants. Their role in a natural setting is to begin the disintegration of wood in forested environments. Wood used in homes is part of nature’s scheme of recycling according to the genetic programming of carpenter ants. As wood ages and is exposed to environmental factors, such as moisture and wood decay, it is more attractive to certain species.

Homes are built in forested or in non-forested areas and when trees are not a part of the natural environment, people plant trees in yards for their personal enjoyment. Like Joyce Kilmer, in the famous poem: "I think that I shall never see a poem as lovely as a tree," people have a reverence for being surrounded by trees. And where there are trees, there will be carpenter ants! Older trees are often the sites for parent colonies of carpenter ants, especially trees that have heartwood exposed due to physical or mechanical damage.

Vegetation plays a crucial role in carpenter ant infestations. Trees and large shrubs provide foraging sites for carpenter ants and where branches touch the roof or siding, foraging routes of ants are easily established. Moisture also moves from vegetation into structures, which make these sites more conducive to infestation. When roots of nearby vegetation grow into crawl spaces, avenues are created for the establishment of satellite colonies within structures, particularly under subfloor insulation and in voids.

Geography is an important factor in that a higher incidence of carpenter ant infestations is found in northern states of the United States. and in southern Canada. However, with the introduction of either coniferous or deciduous trees into urban and suburban areas in other parts of the country, carpenter ant infestations are found in most urban areas in North America.

METHODS OF TREATMENT. Do all members within the colony cause damage? Do some ants bite or sting? Do small ants become larger during the season? Winged reproductives usually raise the greatest fear in homeowners either because they fear this form bites, stings or that this stage can cause more damage. They are, of course, wrong on all counts. No carpenter ants have stings. Neither of the winged forms, male or female, excavate wood. These winged forms are produced in the late summer and require the winter months to complete their sexual development before the nuptial flight in the spring. Males emerge before females and in northern states, these males may make their first appearance in early January. As the temperature fluctuates, the males usually return to over wintering sites but may make several appearances before it is time to fly. If females are overwintering in a structure, they usually make an appearance later in the year than the males but earlier than the winged forms over wintering in nature. The nuptial flights occur in the spring between April and June depending on environmental factors such as rainfall, temperature and sunlight.

Carpenter ants are polymorphic, that is, the workers occur in a variety of sizes from the smallest minors to the larger majors. Adult ants do not grow after development from the pupal stage. Workers will live for several years in both parent and satellite colonies.

A parent colony, which houses the queen, workers and young brood, occurs in areas with high moisture. Satellite colonies, which are extensions of the parent colony, occur in drier areas. Satellite colonies, which contain workers and older brood, are often found within structures where the parent colony could not live. These sites include attics, wall voids and under insulation. Winged reproductives occur in both parent and satellite colonies but most often occur in satellite colonies within structures.

CONCLUSION. Not all infestations are equal in intensity, species, damage, age or conditions. Therefore, all infestations cannot be managed equally. Individualize each inspection. Individualize each management strategy. With new chemicals and formulations available, clients can be offered a menu of management strategies that are appropriate for the season. Understanding the life cycle, species, infestations and the variety of management strategies will provide greater success in management of carpenter ants.

The author is an instructor in biology at Spokane Falls Community College, Spokane, Wash. She can be reached at lhansen@giemedia.com.