Found dead whilst sweep netting a clump of Knapweed
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They are not dissimilar, but the clue is in the name. Dasysyrphus tri-cinctus has three yellow bands, Chrysotoxum bi-cinctum has two. Then, the Chrysotoxum has longer antennae and much more black on leading edge of the wing.
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Lat/Lng: 51.6171, -0.0046
OS grid ref: TQ382928