New Red List of hoverflies in Flanders: extremely useful but often threatened

New Red List of hoverflies in Flanders: extremely useful but often threatened

INBO Researchers have looked at the status and trends of hoverflies in Flanders in order to draw up a new Red List. A little less than half of the species are extinct or threatened in one way or another. And the situation is probably even less positive than these figures tell us...

Hoverflies are colourful flies disguised as bees, bumblebees or wasps, but which do not sting. We can see them in large numbers on flowers all over Flanders. You can recognise them by their aerial acrobatics and typical hovering behaviour. Together with bees and bumblebees, they are among the most important plant pollinators, with an estimated annual global contribution to agricultural production of 300 billion US dollars. They also have great ecological importance as pollinators of wild flowers. About half of our hoverflies are also important natural pest controllers of aphids. So they are very useful insects!

Of the 309 hoverfly species in Flanders, 22 are regionally extinct (7%) and 114 are threatened in one way or another (together 44%).

The observed trend in hoverflies is strongly linked to the condition of their habitat. We notice:

  • a decrease in the species of marshes and other wetlands due to loss of habitat in area and quality, among others due to more and longer droughts
  • a strong increase of forest species, especially those living in dead wood, sap streams and decay cavities, due to less intensive forest use, leaving dead, decaying wood lying around, more old trees in our forests and more ecological forest management

The Red List status of hoverflies in Flanders is relative and probably represents the situation too positively, as we have no data on absolute numbers of individuals per species. In Germany, it was found that the absolute numbers of flying insects, and in particular hoverflies, have declined very strongly over the last decades. This is important because large numbers of hoverflies are needed to fully fulfil their role as pollinators. We therefore urgently need better data to monitor the status of this group of beneficial insects in Flanders.

At the same time, we should not wait to take action. Although we do not yet fully know the causes of the decline, it is clear that the restoration of wetlands and the rewetting of dried-out nature are beneficial, as is the further deployment of ecological forest management with attention to the preservation of old trees and dead wood.

It is not yet clear how important other environmental pressures such as pesticide use and nitrogen deposition are to the decline of hoverflies, but given their precarious status, any additional threat is one too many, especially if we are to maximise the benefits of hoverflies in agricultural and natural areas.

Frank Van de Meutter

Read the report (in Dutch): IUCN Rode Lijst van de zweefvliegen in VLaanderen 2021


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