A. sordida was described by Arthur Gardiner Butler in 1877 using specimens collected by Dr. Hector and J. D. Enys in either Dunedin, Christchurch or Castle Hill.

[2] Butler described this species as follows: Primaries pale shining brown; a small arched marking just beyond the end of the cell, the outer border, and fringe grey; secondaries silvery white; body testaceous: wings below silvery white, primaries slightly brownish; pectus (apparently) silvery white; legs and venter pale testaceous.

Fore-wings elongate, narrow, costa slightly arched, distinctly sinuate in middle, apex round-pointed, hindmargin extremely oblique, slightly rounded; light fuscous, sometimes slightly mixed with darker; a straight narrow tolerably well-defined blackish longitudinal streak somewhat above middle from base nearly to apex, tending to be very slightly interrupted at 1⁄3 and 2⁄3, rather suffused beneath towards apex and near base, sometimes entirely obsolete; when obsolete, there are sometimes visible an arched fuscous mark before 1⁄3 and another just beyond middle, which are usually obscured by the streak; a slender very obscure fuscous transverse line from 3⁄4 of costa to 3⁄4 of inner margin, twice angulated above middle, usually terminating the longitudinal streak, often obsolete : cilia light fuscous, with a cloudy blackish interrupted basal line.

However the brachypterous forewings of A. sordida have a blackish longitudinal streak and the hind wings are rudimentary.

[1] This species has been observed in the South Island, including in Castle Hill, Rakaia, Christchurch and Dunedin.