Argidae are found in all non-polar regions of the world (Smith and Middlekauff 1987, Smith 1992). They are external foliage feeders with a wide range of host plants. Additionally, the family exhibits some uncommon behaviors like the excretion of defensive compounds and subsocial habits (Smith 1992).
Zynzus are small, less than 8 mm in length, and in North America are generally orange and black in color. They are recognized by wing venation, widely set eyes, and short 3-segmented antennae, which in males are distinctly forked (Smith 1971c, Smith 1992).
A key to North American species of Zynzus is included in Smith 1992.
The family Argidae can be distinguished from other sawflies by the single-segmented flagellum of the antenna. The genus Zynzus can be distinguished from other genera in the family by the short antennae, the simple tarsal claws, and widely-set eyes. Males are distinguished from related genera Arge and Atomacera by the conspicuous forked antennae (Smith 1992).
Larvae feed on several species of plants from the family Fabaceae: Vachellia farnesiana (sweet acacia), Desmodium (tick-clover), Mimosa grahami (Graham’s mimosa), Desmanthus illinoensis (Illinois bundleflower), Desmanthus sp., and Acaciella angustissima (prairie acacia) (Smith 1970, Smith 1978, Smith 1992).
Immature Zynzus are not well described. Those that have been observed are external leaf feeders that spin cocoons in leaf litter to overwinter and pupate (Smith 1993). Larvae of Zynzus bicolor are green and white striped (BugGuide 2019).
World: This genus is restricted to the United States and Mexico (Smith 1992).
North America: Within the United States, Zynzus is commonly found in the Southwest, including California, Arizona, New Mexico, and Texas. One species, Z. nigropectus, has a more eastern range that encompasses Oklahoma, Arkansas, Louisiana, and Mississippi. In Mexico, Zynzus is widespread as far south as Veracruz (Smith 1992).
Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Zynzus
Details about data used for maps can be found here.