Ants have consistently ranked as the No. 1 pest in the structural pest control industry. These ants can be either nuisance/troublesome pests or wood-destroying pests. Ants are a diverse group with numbers approaching 14,000 species worldwide. Effective treatment of ant infestations requires correct identification and with the expanding numbers of ant species and the transport of ants from other areas, this is challenging even for the best extension specialists and pest management professionals.
Common names are used for many ants. For example, Argentine ant is the accepted common name for Linepithema humile and Pharaoh ant is the accepted name for Monomorium pharaonis. Problems occur when PMPs and homeowners create their own common names to describe an ant pest. The Entomological Society of America has approved a list of common names for some of these species but common names have not been formally approved for others. Hence, in many cases, the scientific name is used or a descriptive name is created. These names can therefore vary with different localities and personnel and be confusing.
The little black ant (Monomorium minimum) is a good example. The common name, little black ant, is the accepted common name but unfortunately “little black ant” is often used to describe any small ant that is black or dark in color. Infestations of small ants black in color may be odorous house ants, pine tree ants, pavement ants and certain species of cornfield ants (moisture ants). In reviewing trade journals, the little black ant ranks high in surveys of pest ants. Is this ant being identified correctly or are all small ants black in color included in these counts?
Another common name that has been used to describe stinging ants is the term “fire ant.” Unfortunately, this term has been applied to the red imported fire ant (Solenopsis invicta), the black imported fire ant (S. richteri), the tropical fire ant (S. geminata), the southern fire ant (S. xyloni), the European fire ant (Myrmica rubra), the impressive fire ant (M. speciodes), the little fire ant (Wasmannia auropunctata) and others. The term “fire ant” has even been applied to Formica spp., particularly species that have a red-colored head and/or thorax. These ants do not sting but can inflict a painful bite.
Many of these “fire ants” are exotic or tramp ants and have become problems in particular areas because their colonies become large with multiple queens. These ants are often aggressive and eliminate native ants. The red imported fire ant, introduced from South America about 70 years ago, is found throughout the southern states, California, and reported in other states on the East and West Coasts of the United States. The European fire ant, introduced from Europe into New England states in the early 1900s, has spread throughout New England and into other northeastern states, plus southeastern Canada and along the St. Lawrence River as far west as Lake Erie. This ant also has become established in southwestern British Columbia and in Washington state.
Most recently, the impressive fire ant, native to Europe, has become established in Washington state and British Columbia. The little fire ant has become established in several of the Hawaiian Islands. These ants may become problematic because the workers will defend their colonies by stinging people and may cause serious allergic reactions.
Species of Formica (also known as thatching ants) do not have stingers but will defend their colonies with bites and spraying formic acid. Colonies located in close proximity to homes and recreational areas cause problems although generally reactions to formic acid are not of concern. These ants are native and important predators on other insects. Control should be limited to only those colonies that seriously affect human activity.
WHY WORRY ABOUT ID? Ants are a major part of the pest management industry. Both Hedges (2010) and Klotz et al. (2008) cite 35 common names for pest ants. These lists include “carpenter ants” as one common name (but there are 24 species of carpenter ants in North America that are pests!); the common name for cornfield/moisture ants includes 11 species and the Formica spp. includes 20 species. Individual species of ants numbering more than 100 are considered pest ants in North America. Each of these species has unique characteristics related to biology, behavior and habitats. Understanding the differences and similarities of ant species provides information allowing for the most effective control.
Exotic or tramp ants are being introduced into new areas through commerce by the transportation of building materials, plant materials, household goods and the movement of products and people. Changes in environmental conditions, particularly in housing and commercial buildings such as interior atriums, indoor gardens and houseplants where exotic plants are established, may accidentally introduce new insect species, particularly ants. The global distribution of Pharaoh ants and Argentine ants are prime examples.
THE ROLE OF INDUSTRY? PMPs are on the forefront in detecting new introductions, alerting officials and eliminating the establishment of these ants into new areas. Here are PMPs’ responsibilities when it comes to seeing and recording new ants in their areas:
- Identification of ants from infestations. There are a number of photographs and taxonomic keys available either in the form of books (Hedges 2010 or Klotz et al. 2008), extension bulletins, Internet sources, trade publications and teaching aids from chemical companies/suppliers.
- Recognition of a new ant. In inspections or treatments, recognize where there are differences in appearance or behavior in the ants. Field identifications may be difficult in the case of an unknown species. Ants should be collected in a small vial of alcohol to be examined later or sent to someone for positive identification. Hand sanitizers contain about 70 percent alcohol and make perfect collection containers if another container is not readily available. Check the identification with references or contact another professional. Photographs sometimes can be helpful and can be emailed to professionals for identification.
- Record when a new species is identified at your location and where it is being collected. This will assist in determining if it is an established species and the area of infestation.
HOW ARE ANTS MANAGED? An ant is an ant, but not all ants are the same. This is often a difficult concept for homeowners to accept. All ants belong the Family Formicidae. Consider another unrelated family: Felicidae (the family of cats). This family includes the lion, tiger, jaguar, leopard, lynx and the house cat (plus others). Each of these members of the cat family have sharp canine teeth, retractable claws, rounded heads, short muzzles and are hunters with excellent eyesight but distinctive differences in appearance and behavior of each can exist.
So what does this have to do with ants? The family of Formicidae contains more than 14,000 species but all have elbowed antennae, a pedicel (waist), a node(s) and all are social with a queen(s), workers and drones. Each species of ants is as different as the individual species in the cat family in appearance, biology and behavior. Therefore, ants can best be managed if the specific species is identified and differences in biology and behavior are recognized.
Management of ants starts with the proper identification. The next step includes location of their habitat or harborage, followed by non-chemical alterations and finally chemical control. Location of the habitat includes determining where the ants are nesting: soil, wood, wall voids, trees, outdoors or indoors. Identifying and locating foraging trails are important. Trails are seasonal and may be indoors or outdoors. Non-chemical control includes correction of conducive conditions, such as removal of food sources and alteration of harborage. This includes sealing entry points of cracks and crevices and removal of vegetation in contact with the structure. Environmental alteration also includes proper ventilation, correction of moisture conditions and removal of foraging trails.
Chemical control includes the use of baits, dusts and sprays to the perimeter and foraging trails. Baits may be granular, liquid or gel and should be placed in or close to foraging trails. Dusts are effective when placed into wall voids where the ants are either trailing or nesting. Sprays should be directed to the perimeter of the structure, particularly under the lower edge of siding when available, to reduce the breakdown of chemical by sunlight and rainfall. Sprays also may be used in the interior on trails or harborage sites and on the exterior to foraging sites. It is imperative that all label directions be read and followed. A menu approach should be followed so that a variety of strategies can be used as species differ and infestations differ. One size does not fit all species of all infestations. Ant management can be challenging but variations in non-chemical alterations and the menu of chemicals available will enable success.
The author is an instructor in the biology department at Spokane Falls Community College, Spokane, Wash. Email her at firstname.lastname@example.org.
Hedges, Stoy A. 2010. Field guide for the management of structure-infesting ants. 3rd edition. GIE Media, Richfield, Ohio.
Klotz, John, L. Hansen, R. Pospischil, M. Rust. 2008. Urban ants of North America and Europe, Identification, biology and management. Cornell University Press, Ithaca, New York.