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There is one similar on your link heathfied, but I googled 'killer bees -images' and the one nearest to the one I saw was the africanized honey bee. When I try to send a link it never works for me so sorry can't post it. It may have been a hover fly but they seem to have stripes rather than smudgy patches which mine had. I hope I don't see another one anyway, thank you all for replying.