Hi Helen. I had been puzzled by these structures for some time until I just happened to see the picture on p. 38 of Roger F's book where they are identified as cryptocephaline leaf beetle cocoons made from faecal pellets. I have since collected a number of them and beetles have hatched out. The most recent one has been identified as Cadmus ferruginea (sighting 4415802) and the others have all looked similar (eg 4411148). I think the other sighting you mention is the same thing (see 4408331).