What distinguishes Symphyta from the Apocrita suborder?

Symphyta generally lacks the characteristic narrow waist of its relatives.

The suborders Symphyta and Apocrita represent a major phylogenetic split within Hymenoptera, primarily distinguished by abdominal segmentation. The Apocrita suborder is specifically characterized by the presence of a pronounced constriction, often called the 'wasp waist' or petiole, located between the thorax and the first abdominal segments. In contrast, the Symphyta suborder, which primarily houses the sawflies and is considered the more ancestral group, retains a more direct, broad connection between the thorax and abdomen, lacking this distinctive narrow waist. This anatomical difference is a primary marker scientists use to place an insect into one of these two major suborders.