High-Wire Act

The secretary flinched in terror at the sight before her. Having retrieved a potato chip from the bag on her desk, she quickly dropped it when she noticed the two black creatures moving upon it. Ants!

She notified her boss, who called the building’s management company, which then informed their pest control company that quick service was needed. Employees shouldn’t have to share their lunch with six-legged invaders, should they?

Upon arriving, the pest management service professional quickly surveyed the scene. The ants on the desk were acrobat ants. He knew this even without a magnifier because the ants’ abdomens, viewed from above, were in the shape of a heart. In addition, when he disturbed them, several of the ants raised their abdomens up over the top of their thorax in a pose much like that of an acrobat holding his legs bent over his back. If the professional had wanted to confirm his diagnosis under magnification, he would have seen one pair of spines on the top rear of the thorax. He also would have confirmed that the pedicel between the thorax and the gaster (main part of the abdomen) was attached at the top of the gaster and not the middle, as is the case with most other ants.

Having confirmed the ants’ identity, the professional surprised the office workers when he informed them that he was going outside to work and that there was little he could do inside to remedy this infestation. He knew from experience that acrobat ants would not nest inside a six-story, steel-and-glass building. This ant preferred to nest in wood, usually wood that was wet and beginning to rot. The key to quick resolution was to find the nest outside and treat it directly. Sure, he might make a small spot treatment to stop the workers inside the office, but that by itself would only cause the ants to show up somewhere else nearby, such as in another office within the structure.

Outside, it was easy to pick out the column of foraging ants making its way down the side of the building from the direction of the infested office. Seeing the trail turn off to the right at ground level, the professional simply turned and looked for anything made of wood in that general direction. The huge tree 30 feet out on the grounds was the likely source of the ant trail. Sure enough, the trail started from a tree hole in the tree’s trunk and followed the edge of the sidewalk leading up to the building. Worker ants were steadily moving in both directions.

Treatment was rendered in rapid fashion by drilling several small holes into the dead wood of the tree hole and injecting a dust insecticide. Having thus taken care of the colony, the entire length of the trail was treated using a wettable powder pyrethroid. In all, the inspection and treatment had taken just under 15 minutes. Was it a stroke of luck or simply the fact of knowing one’s foe? This professional knew the solution always rides in pinpointing the identity of the pest, a true test of Situational Pest Management. He left to seek out other challenges, secure in the knowledge that his customers would not be “pestered” by these ants again.

This recounting is based on an actual case and demonstrates the value of understanding a pest’s biology in order to render quick resolution to an infestation. It is unfortunate, but most of the service professionals working in the industry today might not be able to recognize an acrobat ant on sight. These ants are important invaders of structures and are more common inside homes and other buildings than might otherwise be expected because they are often mistaken for other species.

How many times has an ant infestation persisted after treatment simply because the time was not taken to confirm the identification? The acrobat ant is one of the easiest ants to identify without a magnifier due to its heart-shaped abdomen, and because it nests inside wet wood, it is often one of the easiest of the pest ants to track down to its colony’s location. This article will discuss the ins and outs of acrobat ant biology and control.

DISTRIBUTION AND BIOLOGY. Acrobat ants consist of a number of different species, six of which are found east of the Mississippi River. Several of these eastern species may also be found in other parts of the United States and Canada.

Crematogaster lineolata (Say), which has many subspecies and varieties, ranges throughout the United States from the Atlantic and Pacific seaboards to an altitude of about 7,000 feet in the Rocky Mountains. Other eastern species include C. ashmeadi, C. cerasi, and C. clara. The California acrobat ant, C. californica, occurs in Southern California and Baja California.

Acrobat ants get their name from the habit of holding their abdomens above their thorax, like acrobats, when the workers or colony are disturbed. In most areas, acrobat ants are only occasional pests within buildings, however, this author has found acrobat ants to be second only to the odorous house ant as a structural pest in West Tennessee and eastern central Arkansas.

New colonies are formed by flights of winged reproductives. These mating flights generally occur from mid-May to late September. The colonies of acrobat ants are typically small, although some colonies may contain thousands of workers. Each colony contains but a single queen. Little is known about their biology.

When disturbed, the workers readily defend the colony, giving off a repulsive odor and biting fiercely. Where the colonies are large, the ants are courageous and sting and bite, but where the colonies are small, the members are timid.

The various species of Crematogaster often live in decaying tree stumps outside and can live in woodwork, particularly door frames or window frames, inside the home. Nests may be found in dead and decaying logs, stumps and limbs outdoors, hollow cavities in trees, in the soil under rocks, in leaf litter, and inside blocks of Styrofoam® used in floating lounge chairs used for swimming pools.

Acrobat ants will nest in wall voids indoors. Much like carpenter ants, they are often associated with wood saturated with moisture from leaks. In fact, these ants will nest in wood already damaged by carpenter ants and termites. This is one of the more common sites to find them inside buildings. Colonies have also been found in association with water leaks around skylights in homes.

In recent years, these ants have been building nests in the foam insulating board called sheathing located behind the siding of homes. One brand of this insulating board is Celotex®. The ants chew off bits of foam, excavating large galleries. The bits of foam are sometimes deposited outside and may be found along the foundation or in window sills.

Acrobat ants feed on a wide variety of foods including both sweets and proteins. Workers are particularly fond of the honeydew obtained from homopterous insects (e.g. aphids, mealybugs and scale insects). These ants will construct “cowsheds” by fixing plant or earthen material over the aphids and scale insects they attend. These ants will also prey on insects, such as termite alates, termites, and the immature stages of the cotton boll weevil, grape curculio and the codling moth. Inside structures, acrobat ants will feed on household foods, showing a preference for sweets.

The workers will readily enter structures by trailing down cables, wires and tree limbs onto structures. Workers crawling onto structures in this manner usually enter the structure through cracks around windows and along the eaves. Trails of workers can also be found crawling across the ground to structures from nests located in stumps or logs. The workers then enter through exterior cracks and under doors. In one situation observed by this author, acrobat ants were found trailing along the sidewalk 105 feet from a tree to an office building. The ants then crawled up all six floors of the building, entering on each floor. In another case, the ants used the branches of the tree in which they lived to access another office building.

MANAGING ACROBAT ANTS. As with any pest ant, the key to effective control of these ants is finding the offending colony and treating it directly. Inspecting for colonies of acrobat ants is similar to inspecting for carpenter ants. When workers are found foraging indoors, the first place to inspect is the exterior of the structure, especially along the building’s foundation where trails of workers are likely to be seen. Be aware of bits of foam insulation along the foundation, indicating ant colonies living in insulating wall board behind the siding. Workers may be observed trailing on tree and shrub branches which brush against the structure. Wires and cables are another avenue for worker ants trailing onto the structure. To avoid potential electric shock, all wires or cables should not be touched.

The eaves of structures should be inspected for ant trails or workers entering cracks in the soffits. Signs of excess moisture should be noted along the fascia boards and under the soffits. Such signs include warped boards, peeling paint and fungi on the surface of wood. Suspect areas in the soffits will need to be inspected more closely using a ladder.

Items such as logs, stumps, dead tree limbs and hollow cavities in trees should be checked for acrobat ant nests. Workers of colonies in these areas can be chased into the open by injecting a flushing agent, such as pyrethrum, into holes in the dead wood. Loose bark can be peeled away which often exposes the colonies. Colonies may also be located beneath stones and debris lying in contact with the ground. Firewood stored both next to and away from the structure may also be a source for an infestation.

Inside structures, acrobat ant colonies are most often found in areas where water leaks have occurred. It is important to ask the customer if they are aware of any water leaks in the building within the past several years. These areas should be inspected first. A moisture meter is helpful in locating areas of high moisture. Firewood stored inside should also be checked for ant colonies.

Termite damaged wood should be probed for the presence of colonies, particularly in basements and crawlspaces. When acrobat ants infest wood damaged by other insects, they often clear out bits of dirt and dead insects. This debris is often deposited in piles in visible areas and indicates the presence of an ant colony. Bits of foam in window sills or on door thresholds may indicate ants infesting foam insulation.

Colonies of acrobat ants sometimes can be detected using an electronic stethoscope if the inspector has excellent hearing; however, it is difficult to hear them using an ordinary stethoscope.

For long term relief from acrobat ants, it is important that any water leaks be repaired and that attic and crawlspace ventilation be improved where necessary. Dead wood, such as logs, stumps and dead tree limbs, should be removed wherever possible. Damaged fascia and soffit boards may need to be replaced. Firewood should be stacked off the ground and as far away from the structure as possible. Tree and shrub branches which brush against the structure should be cut back. As many cracks and holes as possible in the building’s exterior should be sealed.

Each site identified as harboring a colony or suspected of harboring a colony will need to be treated according to the site.

Acrobat ant colonies living inside wood should be treated using the wood injection method where holes are drilled into the ants’ galleries in the wood and small amounts of either an insecticide dust or aerosol insecticide are injected into the galleries. A number of holes may need to be drilled into the wood to ensure the entire length of the ant gallery is treated.

Acrobat ant colonies living in wall voids should be treated by drilling a small hole into the void and injecting a small amount of an aerosol or dust insecticide.

Acrobat ant colonies living in solid foam insulation can be treated by drilling into the infested area and applying a small amount of dust insecticide.

Acrobat ant colonies living in the eaves (soffits) of the structure should be treated by first removing the siding to expose the nest. The removal of siding should only be done by the customer or a contractor. If the entire colony is exposed, the ants can be removed using a vacuum. The colony can be treated with a small amount of a residual microencapsulated or wettable powder insecticide applied with a compressed air sprayer set on a fine spray pattern.

Acrobat ant colonies living in firewood should be removed by discarding or burning the infested wood. Firewood should never be treated with residual insecticides.

Acrobat ants which are foraging in structures from outside colonies can be kept out of the structure by sealing exterior cracks through which ants enter and addressing the colony nest sites outside. This can be accomplished by drilling into infested wood and treating with a dust insecticide. Where possible, the infested log, tree limb or stump should be removed and discarded.

In many cases, however, the acrobat ant nest infesting a structure is located far above the ground in a tree or is situated on a neighboring property. In these cases, treating the nest itself is not feasible. When this situation occurs, the entire length of the ant trail to the building should be treated using an appropriately labeled wettable powder or microencapsulated insecticide. Such treatment will kill many ants and stop indoor foraging for a short period. Periodic inspections are necessary and subsequent treatments provided when the ants are found to again be foraging to the building.

Stoy Hedges is manager of technical services for Terminix International, Memphis, Tenn.