Calopteryx virgoDamselfly on an invassive plant in France.
That looks suspiciously like what we commonly call Goldenrod here in the USA . . . how did that end up in France?? It's highly prolific here and considered a weed . . . I can only imagine how invasive it is in France! Fantastic shot of the Damselfly!
They came here as a garden plant and like you said they proliferate and they are considered as an undesirable "weed". They have invaded most of our wetlands and there is no turning back now. But the blue on yellow does make a nice contrast.