The gaster is the bulbous posterior portion of the

metasoma The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circula ...

found in

hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...

ns of the suborder

Apocrita Apocrita is a suborder of insects in the order Hymenoptera. It includes wasps, bees, and ants, and consists of many families. It contains the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" ( petiole) formed ...

( bees,

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...

s and

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...

s). This begins with

abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

segment III on most ants, but some make a constricted postpetiole out of segment III, in which case the gaster begins with abdominal segment IV. Certain ants in the genus '' Cataglyphis'', specifically ''

Cataglyphis bicolor ''Cataglyphis'' is a genus of ant, desert ants, in the subfamily Formicinae. Its most famous species is ''C. bicolor'', the Sahara Desert ant, which runs on hot sand to find insects that died of heat exhaustion, and can, like other several ot ...

'' and ''

Cataglyphis fortis ''Cataglyphis fortis'' is a species of ant in the subfamily Formicinae. Found in Tunisia, the ants inhabit salt pans where they forage dead arthropods. Navigation skills and internal pedometer Measuring the sun's angle This ant ventures far f ...

'', have a cubiform petiole that allows them to decrease their

inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...

(and therefore increase their speed) by raising their gaster into an upright position.

References

Insect anatomy {{insect-anatomy-stub de:Gaster