Last modified: Feb. 25, 2021, 3:32 p.m.
A common species throughout Belgium.
Parthenogenetic species, adult females are apterous. They can be distinguished from females of Dahlica lichenella by the foreleg which in D. triquetrella always has 5 tarsal segments, whereas in D. lichenella there are only 4 tarsal segments which are sometimes fused.
The occurrence in Belgium of Dahlica inconspicuella (Stainton, 1849) should not be ruled out, but needs a detailed study (see Arnscheid & Weidlich 2017: 55–56).
A cross-section of the case is triangular, this character distinguishes this species from Dahlica lichenella in which the cross-section of the case has a round shape. It is made from silk, and covered with fine sand, soil and even particles of dead insects. Other Dahlica species do not include insect particles in their case.
One generation a year: the males fly from March till May.
Preferably in xerothermic habitats in forests with a lot of Fagus, but also in meadows with a lot of undisturbed lower vegetation.