This is a video about hoverflies.
From Natuurmonumenten in the Netherlands:
Natuurmonumenten works for hoverflies, a group of insects with 328 species in the Netherlands. In the Nieuwkoopse Plassen (Zuid-Holland province), for example. …
Recently, species #328 was discovered, the “verborgen sapzwever”. The book ‘De Nederlandse zweefvliegen’ [The Dutch hoverflies] will be published in the summer of 2008 by Naturalis and Stichting EIS-Nederland.