It prefers mountainous habitat but can be found down to sea level in the southern parts of the South Island.

Larvae likely exist on a variety of herbaceous plants but have been recorded as feeding on species within the genus Plantago.

[3] Hudson used the two female specimens of the moth collected by Averil Lysaght in December 1920 on Mount Taranaki.

[2] In 1924 Alfred Philpott, thinking this was a new species, described this moth under the name Melanchra furtiva from specimens collected around Mount Arthur as well as in the mountainous areas near Lake Wakatipu.

Body rather dark purplish-grey on back, pale green below lateral line, with a very irregular paler intermediate area of dull orange-ochreous; a very broken pale subdorsal line, its components slightly convergent on each segment; eight very conspicuous black bars on the lateral portions of segments 5-13 [A1–A8], with a distinct paler patch behind each bar; these bars terminate on the spiracle and are charachteristic; legs and prolegs green, tipped with brown.

The fore wings have the costa nearly straight and the termen rather obliquely rounded with slight sinuations; pinkish-brown much suffused with grey, especially towards the base and termen; the principal markings are very finely indicated in black; there is a conspicuous curved longitudinal streak from the base to about 1⁄8; the first line is indistinct, very wavy, faintly outlined in brown; the claviform is small, cone-shaped; the orbicular is large, irregularly oval, almost wholly outlined in black; the reniform is large, rather indistinct, outlined in brown towards the base, but otherwise faintly indicated by grey shading; the second line is very faint, grey, sharply bent inwards before the dorsum; there is a series of dark-edged whitish subterminal dots and a V-shaped dark spot near the tornus; the tornal area is clouded with brownish-ochreous and the cilia are also brownish-ochreous.

The head, thorax, and fore legs are greyish-white, very finely speckled with pinkish-brown; the basal third of the antennae is whitish, the remaining portion blackish.[3]I.

[2] Also the antemedian forewing line is normally distinct in I. mutans where as in I. averilla it is absent or just a hint of pale scaling is present.