Pavement Ants

Overview

Pavement ants, Tetramorium caespitum (L.) are among the most common ant species in Minnesota. The common name “pavement ants” is actually derived from the ant’s unique nesting habits in pavement seams. During summer, these ants will occupy a wide range of pavements and become a nuisance, especially when they find their way into a structure. Although pavement ants do not create any health related risks, they may forage in unsanitary areas and leave debris or contaminated food items behind. Therefore, management of these ants is critical, particularly early in the spring before they produce a large number of ants and become a problem.

Identification

• They are dark brown to black.
• Petiole (that between the abdomen and thorax of a wasp or ant) with two nodes (a localised swelling).
• Thorax uneven with one pair of spines.
• Grooves on head and thorax.
• 12-segmented antennae with 3-segmented club.

Biology

The winged reproductive forms of pavement ants usually swarms in spring. After mating, males die soon while fertilized females (queens) dig in the soil, shed their wings and begin laying eggs in two to three days. Each queen may deposit from 5-20 eggs per day. Eggs hatch in 8-12 days and go through three larval developmental instars (stages) in about 25 days. Pre-pupae stage lasts about 5 days and pupae emerge as workers in 12-18 days. The entire life cycle from egg to adult takes from 43-63 days (Bruder and Gupta, 1972).

Habits

Nesting habits: Pavement ants in outdoor environments normally nest in the soil near or under driveways, slabs, sidewalks and patios. They also nest in lawns in areas with vegetation cover >40% bare ground (Radchenko et al. 1998) or under stones, wood, or boards near water. In indoor environments, they nest under the foundation and within hollow block foundation walls, under floors or in insulation.

Pavement ants are known to be very territorial. Workers will aggressively fight ants from adjacent colonies belonging to the same or other ant species.

Reproductive habits: Usually there is one functional queen per colony. Winged reproductive ants undergo mating flights in the spring to form new colonies. Anyhow, in warm areas or in heated buildings, a swarm may occur at any time of the year.

Feeding habits: Pavement ants are omnivorous, meaning they eat both plant and animal items, but they prefer fatty or greasy food. Their normal diet consists of dead arthropods, including insects and carcasses of small vertebrates, such as birds, mice, frogs, etc. (Radchenko et al. 1998), but they will feed on sweets and the honeydew from aphids as well.

Management

Inspection

A thorough inspection is essential to outline the areas of highest or potential ant activity, as well as to identify conditions conducive that directly or indirectly lead to ant infestations. These conditions include, but are not limited to, current or past water leaks or damage, sanitation issues, entry points into structures, etc. Inspection findings are helpful to select the best treatment options and in prevention programs.

Insecticide Treatments

In areas commonly infested with pavement ants, it is recommended to apply two perimeter treatments. The first treatment should be applied during the spring to manage ants before they become a problem, while the second treatment should be done in the fall to reduce the number of ants entering into a structure, especially when outdoor food sources are scarce. These applications are designed to place an insecticide barrier around the exterior foundation walls to intercept any ants attempting to enter or leave a structure, but if ant’s nests or trails are found, they can be treated directly with an approved insecticide. However, if there are any tree limbs or shrubs touching the building, it is recommended to contact a professional tree trimming company to correct that problem so that ants cannot enter a structure directly from the tree and bypass the perimeter treatments.

Perimeter applications are usually accompanied with applications of crack, crevice and spot treatments around any entry points that may provide ants with access into the interior premises of the structure. These entry points include holes in windows, doors, vents, wires, pipes, and attached fencing, porches, patios and flower boxes.

Like other ants, the treatment of pavement ants is usually performed with “non-repellent” insecticides, which are not detectable by the ants and are transferred to other individuals as they feed and groom each other. During this process, the product is shared throughout the colonies resulting in the elimination of the entire colony. Therefore, ants may continue to be seen after treatment until the entire colonies die. This usually accomplished in two weeks.

When pavement ants are frequently seen in a structure, especially during the winter, an approved insecticide can be carefully applied to potential ant activity areas, such as bathrooms, kitchens, laundry areas, furnace rooms, and doorways, where ants may be foraging for food and water. To maximize the effectiveness of the indoor treatment, baits, especially gel formulations can be applied in conjunction with non-repellent liquid insecticides. Gel baits can be applied as cracks, crevices, and spot treatments in corners and out-of-the-way places. Besides, ant bait stations can also be used to help rid of ants indoor for good. Prior to bait treatments, it is highly recommended to thoroughly clean any spilled food items and save food in tightly covered containers, otherwise competing food sources will render the baiting efforts useless. Anyhow, due to the slow acting nature of certain baits, ants may be eliminated within the two to three weeks following the treatment.

Prevention

Ant prevention is important to sustain long-term ant free environments with no or minimal pesticide applications. The following are some prevention practices that help in ant management program.

Sanitation

• Empty trash cans daily.
• Keep dumpster area clean and lid closed.
• Immediately remove food containers and soda cans from indoor trashcans and throw in dumpsters.
• Remove infested, indoor potted plants.
• Thoroughly, clean any spilled food.
• Save food in tightly covered containers.

Water Management

• Repair leaky sinks and water fountains and fix any water damage.
• Increase ventilation in damp areas and in the crawlspace.

Exclusion

• Seal and caulk all cracks, crevices, holes and any ant's potential entry points to a structure.

Avoid any tree and shrubs parts to touch wall and roof structure.

Useful References

Radchenko, A; Czechowski, W; Czechowska, W. 1998: The genus Tetramorium Mayer (Hymenoptera, Formicidae) in Poland – a survey of species and a key for their identification.  Annales Zoologici 481: 107–118.

Bruder, K.W. & Gupta, A.P. 1972. Biology of the pavement ant, Tetramorium caespitum (Hymenoptera: Formicidae). Annals of the Entomological Society of America, 65, 358 –367.