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Ants’ geniculate (elbowed) antennae, metapleural glands, and strong constriction of their second abdominal segment into a node-like petiole set them apart from other insects in terms of their morphology. The three distinct body parts, or tagmata, are the head, mesosoma, and metasoma.

Between their mesosoma (thorax plus the first abdominal segment that is fused to it) and gaster (abdomen minus the abdominal segments in the petiole), the petiole forms a narrow waist. One or two nodes (the second node alone, or the second and third abdominal segments) can form the petiole.

Tergosternal fusion is the process of fusing a segment’s tergite and sternite together on the second, third, or fourth abdominal segment. It is used for identification. The poneromorph subfamilies Ponerinae and their relatives within their clade were once defined by the fourth abdominal tergosternal fusion, but this is no longer considered a synapomorphic trait.