Hello Sweden, Poland, the Alps, etc., are you reading this? In Finland, the species comes down to the South coast, and it is totally absent in Lappland. The species was named after the late Thorwald Gränblom (Tampere, Finland), who had a decisive role in investigating, which Pug moths do really occur in the country. Some 20 larvae were found only on the border of the Spruce forest (on the RHS in the picture shown). Not a single larva was seen on plants growing among higher grasses, like Calamagrostis arundinacea. Another typical habitat are paths and other somewhat open places in the forest (always Picea abies), with often only singly growing golden-rod (Solidago virga-aurea). It is the only host; you never find larvae on the fresh yellow flowers, but rather on quite dry ones.
The species can be easily identified based on its invariable lateral pattern. The 'inventor' of the species Erkki Peltonen described the pattern as Xmas tree (Norway Spruce). The larvae appear a week or two later than E. expallidata, the pattern of which is composed of strictly parallel lines. The latter species seems to have a little wider habitat spectrum, although they may share the same biotope as well. The life-cycle coincides well with (the bit more southern) Perizoma bifaciatum. Should you find a groenblomi larva, be sure to arrange it photographed. You can pretty well assume that the pupa will never hatch. Because of the long pupal time the losses are often considerable and only a fraction of the pupae produce moths. The yearly differences in its abundancy are large, don't give up! Come on guys, go out and find it!
Finland, EH: Pälkäne (locus classicus), ex larva 11. Sept. 1985, Leg: E. Peltonen,
Finland, U: Hyvinkää, ex larva 21. Sept. 1985, Leg: E. Peltonen,
Finland, EH: Kuhmoinen, ex larva 16. Sept. 1995, 7. Sept. 1996, Leg: K. Silvonen,
Photo © Kimmo Silvonen