Hypoponera opacior is a wide ranging and highly variable species that may actually be a species complex. It nests in rotten stumps in partial shade, grass sod, or beneath stones Workers and queens have a high petiole that is strongly narrowed above in lateral view. Small, reddish brown individuals can be confused with Hypoponera punctatissima, but the latter species has a smooth, shining mesopleuron, and a less elevated petiole than H. opacior.
This last character state is very useful for sorting specimens, but is not easily quantified and requires a little practice in its use. Workers of H. opacior also have conspicuous punctures on the central portion of the mandible, while this area in H. punctatissima is smooth and shining. Male H. opacior have light brown wing veins (unlike H. opaciceps), and are most similar to males of Hypoponera inexorata. The latter species is considerably larger (3 mm or more in length). We have occasionally found ergatoid queens (or workers with large eyes).