small ladybird on french bean, eating aphids.
No interactions present.
If you hadn't made the comment about size I think I would have suggested Harlequin. Some Harlequins can be smaller than usual (the UK Ladybird Survey gives measurements as 5-8mm, with two-spot at 4-5mm, so in theory they overlap). As far as I know melanic two-spots don't usually have the white spots on the pronotum that your photo shows.
If you can find it again could you see what colour the legs and underside of the body are? If black that would suggest two-spot, if brown then Harlequin.
Entomologist and biological recorder
I think this is a harlequin ladybird, though I agree with Martin it depends, to a great extent on how small it was. However, the spots are forward of center, on a two spot they are more central or nearer the rear of the ladybird. Also the shape, two spots are more rounded these have a notch out of them. The final feature are the two white spots near the front; though 2-spot ladybirds in the melanistic form can have 2, 4 or 6 spots they are, to my knowledge, always red.
If you refer to the Harlequin ladybird survey web site (link below) there is a photograph of a harlequin which looks very similar.
Again, I agree with Martin, the underside would be diagnostic.
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