By: Gerry Wegner Ph.D.
Acrobat ants (Crematogaster spp.), are interesting to pest management professionals (PMPs) for a number of reasons. There are about 28 acrobat ant species in North America, with 10 species occurring in Florida alone. Of these, several species have been observed entering structures (including C. ashmeadi and C. cerasi).
Acrobat ant workers (see Figure 1) and male alates (winged reproductives) measure about 1/8 in. (3 to 4 mm) in length, while female alates range from about 1/4 to 5/16 in. (6 to 7 mm) long (see Figure 2).
Some acrobat ant species are primarily brown or black, while others are bi-colored or tri-colored with combinations of black, brown, red and yellow. Like other two-node ants, acrobat ants have a sting. Fortunately, U.S. and Canadian species rarely use their sting, and when they do, the pain is fairly minor and short-lived.
Beginning with anatomy and behavior, acrobat ants differ from most other structure-invading ants in North America in the way the second segment (post-petiole) of the waist (pedicel) attaches to the upper front surface of the heart-shaped gaster instead of lower down on the gaster. There are two prominent spines projecting backward from the rear of the mesosoma (thorax plus abdominal attachment) that are much longer than those on the pavement ant, for example.
Acrobat ants engage in a behavior called gasterflagging, which is flexing the gaster upward over the mesosoma. The result gives the impression that Crematogaster ants are performing handstands – hence the common name acrobat ant. Gasterflagging by the worker ants is accompanied by an upwardly aimed release, from the tip of the gaster, of a volatile allelochemical that serves to repel other species of ants and certain other arthropods.
This behavior may be observed by PMPs while disturbing trailing and foraging acrobat ants.
Also, upon closer inspection, an aggregation of acrobat ants around a food source may be seen to establish a perimeter of workers that gasterflag in an attempt to keep away competing ants of other species.
Another interesting behavior of acrobat ants is their tendency to occupy and nest in the abandoned galleries of carpenter ants and termites in tree trunks, logs and structural wood. Although acrobat ants are considered to be primarily arborial (tree-dwelling), they have adapted to living in damp and rotting wood associated with human structures, including roofing, siding, windowsills and doors.
The foraging trails of acrobat ants are easy to spot during the day, as well as at night. PMPs can readily follow these trails to the location of the colony and to the favored nutritional sources. Honeydew and other sweet liquids rank high on the list of preferred foods. In fact, acrobat ants are among the species that “milk” aphids, scale insects and mealy bugs for honeydew.
Insecticide baits based on sweet liquids and gels have demonstrated usefulness in helping to control acrobat ants in structures. However, the relative ease with which the worker ants can be tracked to their nests make an SOS (seek out the source) approach to control more practical for PMPs to achieve fast and favorable results. Therefore, a strategic injection of the nest with an appropriate residual aerosol, liquid or dust insecticide formulation seems to be the preferred method for controlling acrobat ant infestations.