Morphologically most Pergidae are typically sawfly-like, but they are more diverse in structure than any other sawfly family. In particular the form of the antenna varies considerably in number of segments and from simple to serrate and pectinate or even bipectinate (see image below) and many species resemble members of the sawfly families Cimbicidae, Diprionidae, Argidae, and Tenthredinidae.
Sexual dimorphism is common and reflected in differences in type of antennae, colour, and size. Included are some of the few known apterous sawflies, those of the genus Cladomacra occurring in Papua New Guinea and Indonesia, and a species with brachypterous females, Clarissa tasbates, in Tasmania.
The Pergidae are distinguished from other sawfly families by the reduced wing venation, in particular the following characters:
(a) Radial cell (R) without crossvein
(b) Medial and anal cell of hind wing missing.
(c) Anal cell of fore wing usually not present (exception below).
Pergidae can be diagnosed by the following set of characters:
Antenna with 4 to 25 antennomeres (rarely with 9 antennomeres as in most Tenthredinidae), shape serrate, filiform, capitate, pectinate, bipectinate, or furcate. Labium 1-3 lobed, palpus 1-4 segmented. Macillary palpus 2-6-segmented. Fortibia apically with 1-2 spurs, midtibia with 0-2 preapical spines, and hind tibia with 0-1 subapical spine. Tarsal claws simple. First abdominal tergite fused with metapleuron. Fore wing withoug radial crossvein (2r), anal cell present or absent. Hind wing with cell RS present, without medial (M) and anal cell (A).