A medium-small size (wingspan 2-2.5 cm) broad-winged dull charcoal and white moth. Forewings dull black or dark grey, crossed by a doubled white antemedian and prominent white postmedian band, the later with a faint grey line splitting it in two. Terminal areas grey, with upper half broader and darker, divided by a scalloped white line. Forewing discal spot a small black oval. Hindwings lighter grey, crossed by a series of obscure pale wavy lines, the white postmedian band wider and more prominent. Sexes similar; antennae in both sexes densely and finely ciliate. The smaller black and white E. sperryi is more crisply marked. Most similar to Euphyia intermedia, but greyer and with blurrier markings, not as crisp as in intermedia. The subterminal dark patch of E. intermedia is usually broken by a white streak just below the apex, but is not so divided in alternata. E. alternata also have patches of cinnamon hairs in the outer part of the dark patch on the upper forewing submargin, visible under magnification; these are lacking in E. intermedia.