I was specifically looking for larval feeding of either Endothenia marginana or Cochylis roseana, but fully expected instead to just find Endothenia gentianaeana. Gently pulling the heads apart, carefully looking for larval holes through the seeds, I found nothing until revealing the central pithy cavity where sure enough there was plenty of evidence of E. gentianaeana. I've tried this before with the same result.
Typical head with central pith cavity full of frass
A different head, with frass removed revealing silken chamber
Pupal cocoon within silken chamber
Another head full of frass and pithy particles
Same head, showing emergence hole pre-prepared by larva
Same head, frass moved to reveal full-fed larva
During this exercise I also discovered that the bag of teasel heads contained a lot of various small spiders, none of which looked remotely exciting (= easily identifiable) apart from this funky little beast .....
Diaea dorsata, immature male