CARPENTER ANTS

University of Delaware - Cooperative Extension

Home, Yard and Garden

HYG - 12

Carpenter ants are social insects that live in colonies made up of several different forms called castes. Each caste has its own specific function necessary for the success of the colony. They develop through several stages: egg, larva, pupa and adult. Pupae are legless, white and grub-like. The pupal stage follows larval development and is completed inside cream-colored cocoons, often mistakenly referred to as "ant eggs." The adult is the familiar ant-like insect with 6 legs, 3 distinct body regions and prominent elbowed antennae.

Carpenter ant adults

The carpenter ant is one of the largest ants common to the United States. Adults vary in length from about 1/4 inch (6 mm) for a minor worker, 1/2 inch (12 mm) for a major worker, and up to 3/4 inch (18 mm) for a queen. All have constricted waists, unlike termites. Workers are not winged, but reproductives are. Carpenter ant adults are predominantly black; however, some species show brown, red or yellow on parts of the body and legs.

Carpenter ant development

Under optimum conditions, egg to adult development takes about two months--three weeks each for egg, larval, and pupal stages. However, colder weather may lengthen this period to as long as 10 months.

Development of a mature colony--The few workers to emerge from the first brood pupae are small, but they energetically assume the duties of the colony. They open the chamber to the outside, collect food, excavate galleries to enlarge the nest and tend the eggs, larvae and pupae of the second generation. Workers regurgitate food to nourish the developing larvae. Fed in the same manner, the queen has few, if any, duties except to lay eggs.

During the first year the colony contains the queen, 10 to 20 small workers and various immature forms. If conditions are favorable, the size of the colony increases rapidly in the next few years.

The colony is considered mature when winged reproductives are formed. This occurs in three to six years when the colony contains 2,000 to 3,000 individuals or more. It is unlikely that numbers will increase thereafter, due to the constant drain of the many swarmers produced each year.

Winged males and females may be produced any time, but usually develop in late summer. After wintering in the nest, they swarm in the spring or early summer. From 200 to 400 winged individuals are produced each year in a mature colony.

Usually there is only one queen per nest, but colonies with two queens have been reported.

Carpenter ant nests

From spring through early summer, large numbers of winged males and females emerge from established colonies. Emergence is triggered by environmental conditions and may occur over several days or weeks, which allows for interbreeding of individuals from different colonies. Mating occurs in flight, after which the males die and the females begin searching for a nest site. The new queen breaks off her wings just before or after selecting a nesting site.

Nest establishment

Carpenter ants burrow into wood, not to feed but to make nests. Outdoors, the site selected for a new colony may be a stump, log, fence post, telephone pole, or similar large piece of wood. Wood that is moist or partially decayed is preferred, although cracks and crevices are frequently used as are cavities under the bark of stumps and logs. The dead, often hollow, heartwood portion of living trees is sometimes used. Access is gained through a knothole, axe scar, decayed spots, insect tunnel, or similar defect.

Building timbers that are soft, moist (not wet), and decayed are frequently selected as nesting sites. Occasionally, however, a new queen establishes herself in existing cavities or void areas in wood that is perfectly dry.

Characteristics of a nest

As a colony grows, so does its nest. Workers are constantly cutting galleries in the wood to accommodate the enlarging colony. These galleries are irregular but, in general, are excavated with the grain and follow the softer portions of the wood. Harder layers often remain as walls separating the many tunnels. Openings are cut into these walls at frequent intervals allowing movement from section to section.

Access to the outside may be through natural cracks in the wood. Sometimes, however, the ants cut special openings, or "windows."

Occupied galleries are kept immaculate. Shredded wood fragments from the excavations are carried from the nest and deposited outside. Conical piles of these fragments sometimes build up beneath the "windows" or other openings to the nest. The piles may also contain Inedible portions of insects, bits of oil and sand, empty coats and general debris. This "sawdust" is not always evident, because ants may dispose of it in hollow portions of trees, void areas in structures, or unused galleries in the nest.

Unlike termite tunnels, the walls of a carpenter ant nest are smooth and clean, having a sandpapered ppearance. Nests usually begin in soft, decaying wood while subsequent excavations are frequently made into sound, dry lumber.

What do carpenter ants eat?

Carpenter ants are omnivorous; their diets include a great variety of both animal and plant foods. They don't eat and digest wood as termites do. Honeydew from aphids, scale insects and other plant-sucking insects provides much of their sweet food. The ants congregate around groups of these insects and collect secreted honeydew. Carpenter ants feed on other types of insects, but the aphids usually are not harmed. Indeed, they are even protected in some cases. This phenomenon has led to the popular conception that ants collect and herd aphids much as humans herd cows.

Plant juices, fresh fruits and other sweets are also readily eaten by carpenter ants. Most carpenter ants' animal food consists of living or dead insects and other small invertebrates. Common sweets and meats are attractive to carpenter ants. They readily eat syrup, honey, jelly, sugar, fruit, and most kinds of meat, grease and fat.

Foraging workers collect all the food for the colony. Sometimes this is carried back to the nest, but more often it is ingested where it is found. Later it is regurgitated in the nest for use by the queen, developing larvae and non-foraging workers.

Carpenter ant control

When carpenter ants are found in a structure, it means the colony is either nesting within the building proper, or somewhere outside and merely entering to forage for food.

The most important, sometimes the most difficult, part of carpenter ant control is locating the nest or nests. When this can be done, elimination is relatively easy. Sometimes more than one colony is present in a structure, so a thorough inspection is important. The inspection should not stop when one probable source is located, but should include the total structure and grounds.

Inspection indoors

Carpenter ants are usually associated with a high moisture condition. The optimum development of a colony occurs in wood with a moisture content above the normal 12 to 15 percent. This requires the wood to be wet by rain, leaks, condensation, or high continuous relative humidity.

Typical locations include:

  1. Wood affected by water seepage from plugged drain gutters, poorly fitted or damaged siding, improper pitch of porch floors, damaged flashing, wood shingle roofs (especially if asphalt roofing has been applied over the shingles), between the roof and ceiling of flat deck porches, hollow porch posts and columns or leaking door and window frames.
  2. Wood in contact with soil, such as porch supports, siding and stair risers.
  3. Wood in areas of poor ventilation or condensation such as cellars, crawl spaces, attics or under porches.
  4. Wood scraps in dirt-filled slab porches.

What to look for indoors:

  1. Piles of wood debris ejected from the colony. Do not confuse ordinary sawdust with carpenter ant debris. The latter has a shredded quality, resembling the shavings found in pencil sharpeners. Close examination of the debris reveals many parts of dead insects.
  2. "Windows" or small openings to the nest. These are not always present, since the ants may use an existing crack.
  3. Ant activity. Ants frequently forage in kitchens, pantries, and other food storage areas. They may also be found in bathrooms around sinks and tubs. Keep in mind, however, that even when a nest is established in the structural timbers, very few ants are seen inside the building. They are more active at night than during the day, and workers usually forage for food outdoors.
  4. Swarmers (sometimes found ensnared in spider webs in out-of-the-way places).
  5. Damaged timbers. The wood surfaces probably will not be paper-thin, as is frequently the case with termite damage, so detection is more difficult.

Inspection outdoors

Inspect the grounds. Carpenter ants may travel as far as 100 yards from nest to food source. Workers do not lay down scent trails, used by some other ants, so workers are found scattered about. Look for:

  1. Ants traveling between a nest and food sources. This could be from a tree or stump to a structure, or from one tree to another. Many times vines on buildings are used to gain access.
  2. Tree with overhanging branches or vines in contact with roof or other parts of a structure. Ants frequently travel over branches into a building.
  3. "Windows" or other openings to the nest. In living trees these are usually in knotholes, scars, dead areas, crotch angles, or the like.
  4. Piles of shredded wood debris near posts, firewood, stumps, logs, and trees. Check interiors of hollow trees if possible.

Control methods

Protecting structures from carpenter ants requires ensuring that the desired nesting conditions are avoided and destruction of ants in all colonies in and near the structure.

Prevention

Eliminate high moisture conditions to prevent future attacks and also to prevent fungus infections. Ensure proper clearance between structural wood and soil. Provide good ventilation under the house and in the attic as well as drainage away from the house. Repair or replace roof flashing and roof eaves, porch supports, and other places that are exposed to moisture. Use pressure treated wood or wood pretreated with pentachlorophenol. Remove stumps, logs and wood debris near the house. Store firewood away from the house.

Keep exposed exterior wood in good condition with paint, caulking and sealer as appropriate.

Chemical control

Remove or treat with insecticides any carpenter ant colonies found within 100 feet of the house. Apply insecticides to the nest and nest areas. Dusts are particularly effective for treating nest galleries. They may be used in infested areas instead of, or in conjunction with, sprays. Spraying or dusting an infested area with residual insecticides, without locating and treating the nest, usually does not give complete control. Many foraging workers will contact the insecticide and die; however, some ants are active only inside the galleries, and will survive this type of treatment.

Also, the queen and developing larvae would not be affected. The fact that individual carpenter ants can live for well over six months without feeding requires that the galleries of the nest be treated.

Residual insecticides usually are preferred, but sometimes volatile or contact insecticides may also be useful to flush out and kill carpenter ants. Under favorable conditions, vapors can penetrate inaccessible areas of the nest that cannot be treated directly, thereby aiding in eradication of the colony. Such insecticides should be injected or flushed directly into the galleries.

Many products are available under many trade names. The better ones contain one or more of the following active ingredients, which are listed on the label. Consult the label for specific directions and rates for the following insecticides:

Bendiocarb, boric acid,carbaryl (Sevin) ,DURSBAN CONCENTRATE, DIAZINON, propoxor (Baygon), pyrethrins**, . The come in several formulations, including dusts, baits, and aerosols, for both indoor and outdoor use.

*Ready-To-Use.

**Generally considered effective in flushing out as well as killing carpenter ants. There are a few labels that have directions for tank-mixing these materials with residual insecticides.

Dewey M. Caron

University of Delaware

Cooperative Extension Entomologist

11/90

To the best of our knowledge, all recommendations in this are in accordance with those on product labels. However, if there is disagreement between recommendations in this bulletin and what is stated on the label, always follow the label directions.

Commercial companies or products are mentioned in this publication solely for the purpose of providing specific information. Mention of a company or product does not constitute a guarantee or warranty of products by the Agricultural Experiment Station or Delaware Cooperative Extension or an endorsement over Products of other companies not mentioned.

Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State College and the United States Department of Agriculture cooperating. Richard E. Fowler, Director. Distributed in furtherance of Acts of Congress of March 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, handicap, age or national origin.

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