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These are all Volucella inanis (Syrphidae), a predator of wasp larvae. As this species becomes more common in Britain, there are more and more frequent reports of these larvae from houses (all of which have wasp nests) - one was brought to me at the museum this morning! They are associated with Vespula vulgaris, V. germanica and Vespa crabro. Unlike other Volucella larvae, which scavenge in nests, these actually attack and eat the wasp larvae. (Nothing to do with oak leaves or acorns, Mike!)