Q I found this under my cherry tree – what is it?
A BOB SAYS It’s a wasps’ nest, made by any of several species, and clearly unfinished. Wasps enlarge their nest by adding papery layers to the outside, and they can reach melon, football or even beach-ball size, especially those of larger continental or German wasps. Our native wood wasps make smaller nests, although usually larger than this.
I wonder why your nest has an unfinished outer layer. It may just have been started rather late in the season, or the queen may have been killed before the colony reached a larger size. There is a very remote chance that the ash colour and sparse shell might indicate the wood source that the wasps scraped to make this paper-like material was tarred, creosoted or treated with paint or preservative. This could have poisoned them, although then, as with parasites or disease, I would expect some dead wasps to be left inside.