These thrips were found under sections of acacia phyllode that had been partially chewed through and folded back as seen in the last image. I opened several of these, expecting to see moth larvae or something similar, but they mostly contained these thrips, with or without eggs and larvae. It seems unlikely they could have produced these constructions, so I imagine they belong to the group that opportunistically take over the abandoned homes of other insects. See https://www.ento.csiro.au/thysanoptera/Acacia/AcaciaThrips3.html