When disturbed, these tiny ants exhibit a characteristic behavior of raising their abdomen up over the thorax, hence the name "acrobat" ant. There are several species in the genus Crematogaster with C. lineolata being the most common. They're found throughout the U.S.
Acrobat ants are only about 1/16 to 1/8-inch (1.6-3 mm) long and black, or red and black, in color. They have a pair of stout spines at the back of the thorax and two nodes separating abdomen and thorax. The easiest way to identify the acrobat ant is by its heart-shaped abdomen (when viewed from above) which ends in a point with a stinger. The antennae are 11 -segmented with a 3-segment club.
Acrobat ants tend aphids and other plant-feeding insects, protecting them in return for the sugary "honeydew" they exude. In addition to honeydew, the ants feed on other sweets and high protein foods, including live or dead insects. When threatened, they can be aggressive and quick to bite. Some species also emit a strong feces-like odor as a defense.
Outdoor nest sites are usually in dead wood --tree holes, rotting stumps and logs, under bark, in firewood, or under rocks or stones. Colonies are moderate to large in size with a single queen. Swarming is generally in summer, from mid-June to late September.
The Acrobat Ant as a Pest
Acrobat ants will trail more than 100 ft (30.5 m) along the ground, on utility lines, tree branches, or deck railings and will enter buildings under door thresholds, or through utility conduits or any small opening. Seal and spot-treat openings outside to keep ants from trailing inside.
Indoors, these ants usually nest in moist wood, often wood that has already been damaged by decay or wood-destroying insects. They can be found nesting in abandoned termite, carpenter ant, or wood borer galleries but they don't damage wood themselves. Typical nest sites are in wall voids, window and door frames, skylight voids, and in Styrofoam insulation panels behind siding or in wall voids. You may find piles of debris dumped out of the nest. Ants nesting in void spaces can be physically removed or controlled by injecting the wood or void with an aerosol or dust insecticide.
Key Points to Remember - When acrobat ants are simply foraging inside, look for foundation plants outside that are infested with aphid or other plant pests. Eliminating the aphids on the plants often eliminates the indoor ant problem. To find indoor nests, look for areas of damp wood or Styrofoam insulation.