The life cycles of hawthorn webber and porphyry knothorn moth are similar, with one generation a year:
- Adult moths emerge and lay eggs in July-August
- These hatch into dark brown caterpillars that cause some initial feeding damage and webbing before overwintering as young larvae
- They resume feeding in late spring, when the webbing and damage becomes more extensive and noticeable
- When fully fed in early summer, the caterpillars pupate within the silk webbing
Hawthorn webber moth caterpillars are 12-15mm long when fully grown and they produce extensive white silk webbing that covers their feeding area. Caterpillars of porphyry knothorn moth are a little larger and stouter than those of the hawthorn webber. They spin greyish-white silk tubes, which incorporate fragments of plant material, along the stems, so the webbing is less obvious that that produced by hawthorn webber caterpillars.