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A quarter fewer butterflies, half as many bumblebees and hoverflies seem to be almost totally absent in some nature reserves. Tellers are very concerned about a remarkably bad year for pollinators. And now it even seems to have reached a point where many plants are unpollinated.
Butterfly Foundation biologist Kars Veling is the number one butterfly specialist in the Netherlands. So when he was on Twitter in May expressed concerns about the small numbers he found in Dutch nature, this was the first alarm bell.
But, as Veling knows better than anyone: anecdotal evidence is paper thin. Anyone can shout something. This is why a national measurement network has existed since 1992 for monitoring butterflies. Year after year, in spring and summer, the meters make the same trips every week; more than seven hundred in all.
The spring census ended on May 30. The results presented on Monday confirm Veling’s fears: the number of butterflies seen in March, April and May was about 20 to 30 percent lower than the average for recent years.
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Butterflies have been in decline for decades, just like bees
This means that 2023 threatens to be another bad year. Because the trend itself is downward: the number of butterflies has almost halved over the past thirty years. Since 1890, the butterfly population has even decreased “by at least 84%”.
What about other flying pollinators? There is another group of species that is also measured structurally with a fixed measurement system: bumblebees.
And bumblebees also seem to have gotten off to a bad start this year, says Johan van ‘t Bosch of the EIS Insect Knowledge Center. “At the end of May, only half the number of bumblebees were observed as in recent years.”
Extreme drought leaves scars
Radboud University pollination researcher Constant Swinkels still holds hope that the disappointing early spring sightings were caused by insects hiding during the rain and cold.
A wet March and April may indeed have played a role, according to bumblebee expert Martijn Kos from EIS. But he thinks above all of a delayed effect from the extremely dry summer of last year. The supply of nectar and pollen then decreased. “So fewer bumblebee queens were probably produced,” Kos says. They must found a new colony the following spring.
Veling also thinks the extra hit was the very dry summer. “Very early species, such as the orange tip and lemon moth, did well this year. But they had already completed their life cycle by June last year.” So before the drought gets serious.
The spring butterflies that were to survive in the summer while the caterpillars have declined sharply. “We see the little white cabbages and the little veined whites much less. And also the little foxes, the little fire butterflies and the card are having a very bad year.”
“Amazingly quiet”: almost nothing flies in some places
Other observers fear that in addition to butterflies and bumblebees, even more groups of insects are having a bad year. Gliding seems to be in a sorry state, says Eduard Peter de Boer, of eco-office Fauna X.
He recently carried out a count in the Natura 2000 area of the Drents-Friese Wold. “The end of May is normally the peak time for hoverflies. We had sunshine and no shortage of nectar-rich flowers. But the harvest was five in total!” That’s exceptionally little, De Boer told NU.nl. “It’s been surprisingly quiet this year.”
This image is confirmed by Cyril Liebrand of the environmental agency Eureco. He participates in plant research on flowered river dykes. “I ask people there: look around, do you see anything? Zero comma nada. It really scares me.”
He early on LinkedIn to the experiences of other observers. Reactions poured in from all over the Netherlands, but also from Belgium and Germany. “I estimate two hundred to three hundred people, always with the same confirmation: almost nothing will fly this year.”
Wat zijn bestuivende insecten en waarom zijn ze belangrijk?
- Bestuivende insecten vliegen van bloem naar bloem. Ze drinken daar nectar en verzamelen stuifmeel.
- Het gaat om dagvlinders, nachtvlinders, wilde bijen (waaronder hommels), zweefvliegen en ook specifieke kevers. In totaal komen in Nederland een paar duizend soorten bestuivende insecten voor.
- Deze insecten zijn een onmisbare schakel in de voortplanting van planten. Die kunnen vaak pas zaden en vruchten vormen als bloemen bevrucht zijn met het stuifmeel uit een andere bloem. Ook de menselijke voedselvoorziening is hiervan afhankelijk.
- Vanwege het zeer grote aantal planten is ten eerste een zeer groot aantal bestuivende insecten nodig. Daarnaast is variatie belangrijk. Veel planten en bestuivers zijn van specifieke soorten afhankelijk.
The typical June butterflies are now gone
How will this year be for flying pollinators? “Most of the spring butterflies have now taken flight,” says Veling. “One or two species can stretch it a bit and maybe increase it a bit, like the common blue and the haybird.”
After that, what butterfly watchers today follow the ‘June Dip‘ to call. This does not exist in the countries around us, and specific butterfly species were also flying in June in the Netherlands. For example, the red fire butterfly and the swamp fritillary. “But these are species that depend on flower meadows, and they have declined so much in the Netherlands that they are already extinct here,” says Veling.
Van ‘t Bosch isn’t very concerned about bumblebees yet. Because bumblebees are colony-forming bees, they can still recover during the summer months. But then they will need a sufficient supply of food – not another week of drought. If we look at the climate expectations for the future and also the beginning of June this year, there are few guarantees in this area.
Liebrand says he is very concerned: “A lot of plants depend on pollination. But I don’t see any pollination going on. I hope there are parties that are looking into the causes and taking this seriously.”
Wat valt er te doen aan de insectensterfte?
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