Plant & Pest Diagnostics

Thief Ants (Solenopsis molesta)

The following information was modified from the University of Arizona.

The thief ant takes its name from their habit of nesting close to, and in some cases inside the nests of other ants, from which they steal food.

The length of the thief ant varies from 1/32 inch to 1/8 inch (0.5 to 3 mm), though most are around 1/16 inch. Their color also varies from yellow to bronze to dark brown with a smooth shiny appearance. The petiole consists of two segments. The antennae contain 10 segments terminating in a 2-segmented club. Characteristics also include small eyes and a stinger at the rear of the abdomen.

Due to their variability in size and color the thief ant is sometimes wrongly identified. The pharaoh ant can be similar in size and color. The pharaoh ant is 1/16 inch long and light yellow to red. The pharaoh ant abdomen however has black markings and the hind portion is usually somewhat darker. Further more the antennae of the pharaoh ant have 12 segments with a 3-segmented club.

Colonies of thief ants are generally small varying from a few hundred to several thousand workers and a multitude of queens. Swarmers take flight and mate from June until late fall. The developmental time from egg to adult takes around 50 days to several months.

Habitat

Thief ant colonies are found both indoor and outdoors. Nests are large and often have tiny tunnels connecting to the nearby nests of larger ants from which they habitually steal food and brood. On occasions they have been known to takeover the associated ant nest. Outside they can be located under rocks, around walkways and house foundations, in rotting wood and exposed soil. Indoor nests are found in any small crevices, particularly woodwork and masonry, under floors and behind baseboards.

Foraging and feeding

These ants are prevalent in households, in which they forage for foods with a high protein content such as grease, cheese, meat and hollow out seeds for the oil content. It is important to note that due to their small size, they can easily enter packaged foods. They also feed on immature forms of other ants and scavenge on dead insects and rodents. Unlike most other ants they do not appear to feed on sweets. They travel great distances in search of food, and once a source is located they form a trail from the food to the nest moving in columns of ants. The thief ant, however, is most renown for stealing from other nearby ant colonies.

Distribution

The thief ant is native to the United States and is found throughout the country, though primarily in the eastern and central states.

Management

The thief ant is persistent and may be difficult to control. Pest proof your home and don’t leave food around to attract ants.

Indoor nests are best treated by baiting. To avoid the use of chemical insecticides, a small amount of greasy bait may be placed on wax paper and positioned in the areas of ant activity. More success, however, is found with chemical ant baits, such as Terro, or Drax Ant Bait, though they must be mixed with a grease or oil to make them attractive to thief ants. Any grease or oil that can be mixed with the bait should be effective. For example vegetable oil and peanut butter, though some exterminators recommend a specific recipe of bacon, baking powder, yeast and corn meal. Care must be taken in the mixing of the bait. If too little grease is added the bait will not be attractive to the ants, however if too much is added it will dilute the active ingredient below the level of effectiveness. Unfortunately exact proportions of the most effective mixture are not documented and so this technique requires a little trial and error. One drop of grease or oil should be added at a time until the bait appears to be working.

In the case of outdoor colonies, the most prompt strategy involves direct treatment of the nest site. Colonies may be located by inspection of foraging trails.