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A 40 year study in the same habitat. Minus 80 percent individuals, minus 40 procent species....

The site were I found it: https://www.naturetoday.com/intl/nl/nat ... ?msg=29040
The study (text, pdf and supplement.): https://resjournals.onlinelibrary.wiley ... icad.12577

Must be Syrphidae!