Larva collected from Erica peltata 14 April 2020
https://www.inaturalist.org/observations/42233511

Very uncomplicated, good eater :-)

Stopped eating 21 April and started to spin a light web, which became sturdy cocoon.

When there were still no signs of an adult by 9 Sept, I opened the cocoon to find a bunch of empty wasp eggs. The weave of the netting covering of the jar was obviously large enough that the wasps could escape :-(

CORRECTION: see Marion's coments below - these are the eggs of the moth.
https://www.inaturalist.org/observations/59557891