Last modified: Feb. 17, 2020, 2:01 p.m.
A very rare species in Belgium. Nowadays exclusively known from the southern provinces, where in some places it can be locally very common, especially the limestone area.
Males have wings, females are micropterous. Wingspan 27–28 mm.
Forewing male light russet brown with two tranverse lines, dentate and not strongly distinct, come markedly closer together at inner margin, discal spot elongated. Hindwing a whitish hue, scarcely marked. The general color has a more contrasted appearance than T. primaria.
Females have forewing stumps (just over half of the abdomen) with a greyish background color, dotted with a dark brown blackish transverse band that slightly gets smaller towards inner margin.
Usually found in May and June.
Caterpillars are greenish white, dark green or dark brown in color. The green-white caterpillars have an unsigned form with only a number of white lines, of which the subdorsal are the most striking. The other two color forms have square dark spots on their backs but these are infrequently.
Cannot be distinguished from Theria primaria with certainty.
Pupates as a pupa in litter on the ground or underground. The males fly from dusk onwards. During the night they can be found on bare branches of the host plant, sometimes mating with a female. The flight period is slightly later than that of T. primaria. They come to light.
The adults fly from mid January onwards till late March and because of the early flight period they might be overlooked in some areas.
Hedges, forest edges where the food plant grows.