Wikipedia
Argidae
Argidae is a large family of sawflies, containing some 800 species worldwide, primarily in tropical regions. The larvae are phytophagous, and commonly can be found feeding (and often pupating) in groups, though very few attain pest status. Notable infestation of this family are recent outbreaks of Shizocera sp. feeding on the leaves of the Mo tree Manglietia conifera (Magnolaceae) which have occurred in pure stands of the tree in the northern temperate region of Vietnam.
The family is distinguished from all other Symphyta by the reduction of the antenna to a single elongated flagellomere, which is often shaped like a tuning fork in males.