gasters

Gaster is a term used in anatomy and entomology to refer to the posterior portion of the abdomen in certain arthropods, most notably in ants, bees, and wasps. The word derives from the Greek gastēr, meaning stomach, and in scientific descriptions it helps distinguish the rear abdominal region from the thorax and the anterior abdomen.

In eusocial hymenopterans, the gaster consists of the abdominal segments behind the propodeum and is connected to the thorax by a constricted waist formed by the petiole and, in some species, the post petiole. The gaster houses much of the digestive and reproductive system and often contains venom glands that contribute to the insect’s stinging apparatus. In many species, the sting is located at the distal end of the gaster, making this region a focal point in studies of behavior, ecology, and defense.

The gaster varies in size, shape, and coloration among species and can be an important feature for taxonomic identification. In ants, for example, the gaster’s segmentation, sculpturing, and surface texture are commonly used characteristics. In bees and wasps, variations in the gaster can relate to their roles, mating strategies, and social structure.

Gaster is sometimes used more broadly to describe the rear abdomen in other insects as well, but its precise boundaries and internal anatomy can differ among groups. See also metasoma, petiole, sting, and abdomen for related anatomical terminology.