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A medium-small moth (approx. 2.6-3.2 cm wingspan), females larger than males. Adults are quite variable, ranging from mostly brown-black specimens to light rusty-tan ones, the later most common. Typical specimens have light rusty-tan forewings, shading to sooty brown along the leading edge, in the median area and in an irregular terminal band. A few dark scales indicate the normal lines and spots where they cross the veins, giving the moth a lightly speckled appearance. The reniform is white, with a few dark scales in the center and stands out against the darker ground. Hindwings are light sooty brown with a faint lighter median line. Antennae simple and sexes similar. Specimens largely suffused with darker brown or blackish scales can usually still be identified by the contrasting light reniform. Condica videns occurs in similar habitat, but has pale hindwings and lacks the speckled appearance of fractilinea.

Oligia fractilinea is single-brooded with adults flying in mid to late summer. Adults come to both light and sugar bait. The larvae, from whence comes the common name, are borers in the stems of grasses, in particular Timothy (Phleum pratensis), and in the east are sometimes a serious pest in young corn (Zea).

Widespread in southeastern and southern North America, from New Brunswick west to Alberta, south to Florida and Arizona. In Alberta fractilinea is restricted to the grasslands region, and in particular dunes areas. It has been collected north to Edgerton and west to Lethbridge.