Editor’s note: The following article is excerpted from the PCT Field Guide to the Management of Structure-Infesting Ants, Third Edition, by PCT Contributing Editor Stoy Hedges. The book, currently in the final stages of editing and production, will be available in November.
Rover ants are very small ants about 1⁄16-inch (2 to 3 mm) in length. The single node in the pedicel has a low peak that is sloped slightly forward. The gaster (abdomen) is generally carried forward and hides the node from view, similar to odorous house and ghost ants. The thorax is uneven in shape, but the front portion is strongly humped. The key characteristic is the nine-segmented antennae with no club present. The monomorphic (one size) workers will range in color from amber to dark brown depending on the species.
The primary pest species in this group is B. patagonicus Mayr, an exotic species originally from South America. An unofficial common name for this species is the “dark” rover ant, as the workers tend to be dark brown in color. B. patagonicus is distinguished from other rover ant species (like B. obscurior Forel) by its large eyes and several long, erect hairs present on the mesonoma on the top of the thorax. Seeing these differences, however, requires an experienced eye.
Biology & habits. Brachymyrmex species are widely distributed in Florida and along the Gulf Coast into Texas where they are becoming an increasing pest seen in homes. B. patagonicus is the primary species found infesting homes within this range, and it is well established along the Gulf Coast, in central Texas and is reported in Phoenix and Tucson, Ariz., as well as Las Vegas.
Key Biology Points. Five species of Brachymyrmex are found in Florida and eight species occur throughout the U.S. In a survey of Florida’s structure-infesting ants, two species, B. obscurior and B. patagonicus, were the most common species seen in homes. Swarms of alates indoors or in swimming pools were often the pest problem caused by these ants. Hundreds of alates end up in pools inside screened pool enclosures, resulting in homeowners needing to spend time removing them prior to using the pool.
Colony Structure. Colonies are generally small and contain but one queen. Several colonies to many colonies are commonly present around those homes that suffer chronic infestations of B. patagonicus.
Nesting Habits. These ants primarily nest in the soil but also will be found in moist or rotting wood and leaf litter. Colonies have been discovered inside structures in boxes near water heaters and sinks. Don’t rule out potted plants as a source.
Landscape mulch is also a common nesting site. One pest management professional confirmed rover ant colonies in and around bags of mulch at hardware centers in the Dallas-Ft. Worth area. Bagged mulch may be one of the ways this ant is spreading to new areas.
Fungus-damaged wood in homes might also be used as a nesting site. Subslab colonies are possible with this species. In these cases, infestations may first be detected when the alates swarm into the building.
Foraging Behavior. These ants often forage under the soil’s surface along roots where subterranean aphids and mealybugs may be found. Foraging workers seen inside generally appear in the kitchen and bathrooms. The numbers seen are typically not large, but the regular presence of tiny ants on counters and floors is disconcerting to most homeowners. Rover ants can be found foraging outside on walls, fences, decks, sidewalks and other items.
Feeding Habits. A major food source for this species appears to be the “honeydew” produced by subterranean aphids and mealybugs that feed on the roots of plants. Rover ants also require protein and have been observed feeding on dead insects and foraging around trash containers.
Colony Propagation. New colonies are formed by mating flights of winged males and females. Swarms occur in the evening during the summer, and the swarmers are strongly attracted to lights. It is the lights in swimming pools that draw these winged alates to the water where they collect by the hundreds. Many homeowners report interior infestations involving only the alates.
KEY INSPECTION TIPS. Typically, ants seen inside are the result of incursions from colonies outside. Look for ants foraging on fences, walls, sidewalks, etc. Pre-bait using drops of jelly or sweet ant gel bait to discover ants and to create trails to follow. Check any piles of leaf litter and lift stones and other items in contact with the soil for colonies underneath.
Inside colonies of this ant are most likely to occur with a source of excess moisture so a moisture meter can be a handy tool. The homeowner should be questioned regarding past water leaks, and such areas will require close inspection. Bathrooms seem to be an attractive site, particularly where past water leaks have occurred. Evidence of excessive moisture in walls may be inspected more closely by opening the wall, but the homeowner’s permission must first be obtained.
Subslab colonies may be indicated only by the emergence of swarmers. Pulling carpeting back may be necessary to pinpoint where in the room the ants are emerging. If this is done, the customer must realize that they may need to hire a carpet installer to reposition the carpeting following treatment.
CONTRIBUTING CONDITIONS. Outdoors, changing out landscape plantings for those less prone to aphids may be helpful. Tree and shrub branches should be trimmed well away from the building’s walls and roof. Gutters should be cleaned and any leaf litter removed. Indoors, water leaks should be repaired, and the surrounding void and wet wood thoroughly dried. In many cases, correcting the moisture conditions results in the ants vacating the structure. Severely water-damaged wood should be replaced.
MANAGEMENT. Infestations of these ants are best managed by locating and treating all colonies inside the structure. B. patagonicus infestations can be frustrating to control and many of the common control strategies don’t provide any long-term relief. In such cases, it is likely the property has numerous rover ant colonies around the home and probably one or more inside.
Because each colony is a single entity unto itself, successful control depends on finding and treating as many colonies as possible as well as employing the use of sweet-containing gel or liquid ant baits to control hidden colonies. For some situations, more frequently scheduled service visits may be needed to continue to find and treat overlooked nest sites and to replenish ant baits.
Pre-baiting using jelly or drops of sweet ant gel bait is a good strategy to determine the extent of the infestation and to establish trails of workers that can be followed. Pre-baiting also can be done inside, but the pre-baits should be placed on pieces of card stock, in short pieces of plastic straw, or another method (e.g., Ant Cafe, BaitPlate) that allows retrieval after the trails have been established.
Ant swarmers inside buildings are best removed using a vacuum.
Ant colonies living in the soil or underneath items, such as stones or logs, can be treated by drenching each individual colony with an appropriately labeled residual insecticide using a compressed air sprayer or backpack sprayer. Raking through the soil with a small hand rake before and after treatment will allow more thorough penetration throughout the colony.
Landscape mulch may need to be raked back and the area underneath treated where ant activity is found. This technique may be necessary where difficult rover ant infestations are encountered.
Ant colonies living in wall voids can be treated by drilling a small hole into the wall void over the site of the colony and injecting a small amount of an appropriately labeled aerosol insecticide. An appropriately labeled residual insecticide applied with an Actisol, or similar aerosol-generating machine, also can be used.
Correction of any excess moisture conditions can be completed either prior to or following the treatment.
Perimeter treatments with a residual liquid insecticide have not proven effective for any long periods in deterring ants seen inside. Use of non-repellent residuals (e.g., fipronil, imidacloprid) to foundations also provides short-term relief. A strategy of finding and treating colonies combined with baits seems to achieve the best results (although sometimes this success is fleeting).
Ant baits can be successfully used to reduce numbers of B. patagonicus workers around a home, especially when using liquid ant baits. Liquid ant stations may be installed outside using an appropriate ant bait station placed at the base of trees or shrubs, by fence posts, or where ants are found foraging as well as along the foundation where ant activity is known (e.g., by pre-baiting). Keep in mind that such stations outside need to be located where children and pets should not be able to access them. Sweet ant gel or syrup baits also may prove acceptable to some colonies of rover ants, and these may be the preferred choice for use indoors. Place baits in stations in areas accessible to ants but not to children or pets. Follow-up visits are generally needed to see if the ants are foraging on the bait and to replenish bait that has been consumed.
Treatment of plants and trees that are infested by homopterous insects, such as aphids, may be beneficial in reducing rover ant populations; however, no studies have been done to prove this strategy’s effectiveness. Such treatments need to be conducted using the proper turf and ornamental state license.
New Rover Ant Bait Introduced
Rockwell Labs Ltd recently introduced InTice Rover Ant Bait, a thick syrup bait similar to InTice Thiquid Ant Bait, but with a unique attractant matrix that is particularly attractive to rover ants, according to CEO Cisse Spragins. “Rover ants have emerged as a serious pest in Florida, Texas, Arizona and the Gulf Coast in recent years,” she said.
In Spragins’ experience, rover ants tend to become a problem in accounts where non-repellent liquid insecticides are used. “It’s as if the non-repellents wipe out other ants, which then clears the way for these ants. These ants can be quite a problem due to their strong propensity to enter structures,” she said.
InTice Rover Ant Bait, currently registered in Florida and Texas, is part of Rockwell’s “Green Zone” line of products. The new product is packaged in 16-ounce bottles and labeled for use in both food and non-food areas of structures. A number of other ant species also are included on the label, including Pharaoh ants.
“The bait may be placed directly on flat surfaces and is thick enough that it will not run,” Spragins says. “For slanted or vertical surfaces, or any surface where direct contact with the bait is undesirable, Rockwell’s BaitPlate station can be used.”
To make a liquid bait, PMPs should mix one part InTice Rover Ant Bait with one part water for a 2.5% dilution. The diluted product also may be sprayed directly on the foundation and other surfaces outdoors, according to the manufacturer.
Rockwell Labs develops, manufactures and markets products specifically for the pest management industry. Each of the company’s formulated products are manufactured and packaged at its North Kansas City, Mo., manufacturing plant.
To learn more about InTice Rover Ant Bait or to download a label or MSDS, visit www.rockwelllabs.com , call Rockwell Labs at 866/788-4101 or contact your local distributor.