Caltha palustris flowers are a favourite nectar source for many hoverflies, including Syrphus ribesii [1].

References
1 Nederlands SoortenregisterSyrphus ribesii♂︎
Caltha palustris (Marsh-marigold)OBSERVATION:
2023-IV-15
Caltha palustris flowers are a favourite nectar source for many hoverflies, including Syrphus ribesii [1].
References
1 Nederlands Soortenregister