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A medium-sized (3.8 - 5.0 cm wingspan) narrow-bodied rather drab mottled dark and light grey moth. The dentate white subterminal line is the most prominent marking and is bordered inwardly by small black wedges. Claviform, reniform and orbicular spots white outlined and largely filled with grey scales and thus rather obscure. Hindwings light grey with a dark discal dot, faint postmedian line and narrow, dark terminal line. Antennae simple. Sexes similar. Speciosa looks blurry and lacks the crisp contrasting dark grey or black appearance of X. mixta, with which it was formerly lumped and is often confused. The male genitalia are distinct. The genitalia of both sexes are illustrated by Lafontaine (1998). In the northern end of the mountains of Alberta speciosa often has dark phenotypes, in extreme cases almost melanic.

Adults are nocturnal and come to light. In Alberta adults are on the wing from late June through mid-August. The larva is described by Lafontaine (1998). Speciosa is polyphagus, and reported larval hosts include blueberry (Vaccinium spp.) (Ericaceae), Dwarf birch (Betula nana) (Betulaceae) and goldenrod (Solidago spp.) (Asteraceae) (Lafontaine, 1998).

Holarctic. X. speciosa is widespread across the northern Palaearctic. In North America it is distributed across the arctic from AK west to Hudson Bay and south in the Rocky Mountains to CO. Two subspecies occur in North America; subspecies arctica Zett. occurs in northern Canada, south to the northern parts of the mountains in Alberta. In the southern Alberta mountains and southward (including Cypress Hills) and south to CO arctica is replaced by ssp. apropitia Benj., a slightly larger darker form that was described from Banff specimens. Speciosa is found in coniferous and mixedwood forest.

Recent work on this genus by Mikkola, Lafontaine and Kononenko (1996) has resulted in a better understanding of the subgenera as well as some major changes in the nomenclature. It is possible that with further research the North American forms may yet prove to be one or more species separate from Palaearctic speciosa. Hodges et al (1983) treated speciosa and apropitia as separate species, hence the dual MONA numbers. The illustrated specimen is subspecies arctica from YT. Most Alberta material examined tends to be broader-winged and frequently is darker.