Heteronympha cordace has a wingspan ranging from 38–42 mm (1.5–1.7 in), with females generally larger than males and with stouter abdomens.

It is not common in any areas and colonies tend to be static, and many populations have become extinct as a result of habitat loss.

It is fond of sedgeland and low shrubland in swamps and along creeks, often with dense stands of the larval food plant.

[3] The female butterfly lays a single egg or very few on the underside of the lower leaves of Carex appressa.

The eggs are .8 mm (0.031 in) in diameter, green, nearly spherical, and have thin longitudinal ribs.