Thief Ant, Solenopsis molesta

Characteristics:

  • Coloration: yellowish to light brown
  • Body length 1/32 inch (monomorphic)
  • Antennae club unusually large and elongate, 2-segmented

Thief ants belong to a complex group of very small, related species that have not been studied in detail. The most studied species in this group is Solenopsis molesta.

Colonies of these ants are small, containing several hundred to a few thousand individuals with numerous queens. New colonies are started following nuptial flights that take place from late July to early fall. The winged sexuals mate in flight. A single inseminated female can establish a nest independently and start a new colony on her own. However, during nuptial flights, some females have been observed with one or more workers attached to their body; these workers apparently help the new queen establish a nest. In the laboratory, queens laid between 27 and 387 eggs per day. Workers developed from egg to adult in 52 days. Thief ants are extremely small, less than 1/32 inch in length, and golden yellow to light brown in color. Queens are similar to workers but are much larger (0.16-0.2 in or 4-5 mm) in length. Antennae are 10-segmented with a 2-segmented club that is long and unusually large. They possess a stinger that is visible at the end of the abdomen. Solenopsis molesta are called ‘thief ants’ because they live in the nests of larger ant species and feed their own colony members with food stolen from the host species. They devour host larvae and pupae.

Distribution

The thief ant, Solenopsis molesta (Say) is a native species that ranges throughout the United States. Thief ant colonies are small, containing several hundred to a thousand individuals with many queens. They are highly adaptive in their nesting habits and can nest in exposed soil; under objects on the ground such as stones, logs, bricks, and inside decaying wood in stumps and in woodwork and masonry of homes. They invade homes from outdoors, generally during hot weather. They nest in cracks and crevices and wall voids, forage readily on set trails and are persistent in their forays. They can easily enter packaged food because their small size allows them to enter containers inaccessible to larger ants. They eat a variety of household foods such as meats, breads, sweets, nuts, animal fats, vegetable oil and dairy products. They may prefer high protein foods.

Management

Thief ants can be very difficult to eliminate because the ants are extremely small and nest in remote and inaccessible areas where workers may be seen only periodically. Detection of colonies may take considerable time and effort. Inspections should be made to determine whether the ant is a thief ant or pharaoh ant, because control procedures for each vary greatly. The thief ant is often confused with the pharaoh ant because they are similar is size and color. There are, however, easily recognizable differences. Treatment is relatively simple once nesting sites are located. Drenching each colony with an approved residual insecticide with a compressed air sprayer can treat colonies living in exposed soil or under objects on the ground. Indoors, colonies living in wall voids can be treated by injecting an aerosol or dust insecticide into cracks and crevices around baseboards or in small holes drilled into the wall. But insecticides have not been as effective for control of thief ants as for other species. When baits are used, regular follow-up inspections are necessary so that fresh baits can be in place until the colonies are eliminated.