Thera firmata, the pine carpet, is a moth of the family Geometridae.

Apart from the pectinate male antenna (2 pairs of rather short, slender pectinations to each segment) the paler, more yellowish-tinged hindwing, pale abdomen with red-brown dorsal line, dark subbasal mark along the hindmargin, more deeply angulated antemedian line, more bluish white (or violet-white) subterminal line, usually accompanied by some slight violet-grey shading, and absence of black apical dash all distinguish it.

The typical form, which varies very little, inhabits Northern Central Europe, Switzerland and Austria-Hungary.

ulicata Rbr., from S. France, Castile and Lower Austria, has the ground-colour predominantly of the pale violet-grey or blue-grey tone and the median band darkened.

"[1] The larva is naked, long and thin, green with narrow, light longitudinal stripes.