Pupal cocoons created or ‘spun’ from self-produced silk material are uncommon in beetles, and none are reliably known in the family Cerambycidae. The common lepturine species Pseudovadonia livida has larvae that are exceptional among known cerambycids in developing in soil infested with the fungus Marasmius oreades and pupating in a ‘parchment-like’ cocoon. It has been proposed previously that the cocoon is created by the mature larva, but no gland or other larval organ is known which could produce such a cocoon. Both microscopic inspection of the cocoon material and DNA sequencing indicate that the cocoon is composed of the hyphae of the associated fungus. The fungus is thought to create the cocoon while actively growing but further research is required to determine whether there may be some cerambycid larval stimulus (e.g., chemical). This is currently the only reported example of a beetle pupal cocoon created by active growth of fungal hyphae.