A quarter fewer butterflies, half as many bumblebees and hoverflies seem to be almost completely absent in some nature reserves. Tellers are very concerned about a remarkably bad year for pollinating insects. And now it even seems to have reached a point where many plants are not pollinated.
Biologist Kars Veling of the Butterfly Foundation is the number one butterfly expert in the Netherlands. So when he was on Twitter in May expressed concerns about the small numbers he found in Dutch nature, that was the first alarm bell.
But, as Veling knows better than anyone: anecdotal evidence is paper thin. Anyone can shout something. That is why a national measuring network has existed since 1992 for monitoring butterflies. Year after year, during the spring and summer, counters run the same routes every week; seven hundred in all.
The spring census was completed on May 30. The results presented on Monday confirm Veling’s fears: the number of butterflies observed in March, April and May was about 20 to 30 percent below the average of recent years.
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Butterflies have been declining for decades, as have bees
This means that 2023 threatens to be an extra bad year. Because the trend in itself is a downward trend: the number of butterflies has almost halved in the past thirty years. Since 1890, the butterfly population has actually decreased by “at least 84 percent”.
What about other flying pollinators? There is one other species group that is also structurally measured with a fixed measurement system: bumblebees.
And bumblebees also seem to be off to a bad start this year, says Johan van ‘t Bosch of the knowledge center for insects EIS. “At the end of May, only half as many bumblebees were observed as in recent years.”
Extreme drought leaves traces
Pollination researcher Constant Swinkels of Radboud University still has hope that disappointing observations in early spring were caused by insects hiding during rain and cold.
A wet March and April may indeed have played a role, says bumblebee expert Martijn Kos of EIS. But he thinks mainly of a delayed effect of last year’s extremely dry summer. The supply of nectar and pollen then decreased. “So fewer bumblebee queens were probably produced,” says Kos. They have to start a new colony in the following spring.
Veling also thinks that the extra hit was the very dry summer. “The very early species, such as orange tip and lemon butterfly, did well this year. But they had already completed their life cycle in June last year.” So before the drought got serious.
Spring butterflies that had to survive in the summer as caterpillars declined sharply. “We see much less small cabbage white and small veined white. And also small fox, small fire butterfly and the map are having a very bad year.”
‘Shockingly quiet’: almost nothing flies in some places
Other observers fear that in addition to butterflies and bumblebees, even more insect groups are having a bad year. Gliding seems to be in a sad state, says Eduard Peter de Boer, of ecological bureau Fauna X.
He recently did a count in the Natura 2000 area the Drents-Friese Wold. “The end of May is normally the peak time for hoverflies. We had sun and no lack of nectar-rich flowers. But the harvest was five in total!” That is exceptionally little, De Boer told NU.nl. “It’s been shockingly quiet this year.”
That image is confirmed by Cyril Liebrand of ecological agency Eureco. He participates in plant research on flowery river dikes. “I ask people there: look around you, do you see anything? Zero comma nada. That really scares me.”
He early on LinkedIn to the experiences of other observers. Reactions poured in from all over the Netherlands, and 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.
Typical June butterflies are now extinct
How will this year go for the flying pollinators? “Most spring butterflies have now fledged,” says Veling. “One or two species can stretch it a bit and maybe increase a bit, such as the common blue and the haybird.”
After that, what butterfly observers today follow the ‘junidip‘ to call. This does not exist in countries around us, and specific butterfly species used to fly in June in the Netherlands as well. For example, the red fire butterfly and the swamp fritillary. “But those are species that depend on flowering grasslands, and they have declined so much in the Netherlands that they are already extinct here,” says Veling.
Van ‘t Bosch is not yet very concerned about the bumblebees. Because bumblebees are colony-forming bees, they can still recover in the summer months. But then they will need an ample supply of food – not another weeks-long drought. Looking at the climate expectations for the future and also the start of June this year, there are few guarantees in that area.
Liebrand says he is very concerned: “A lot of plants depend on pollination. But I don’t see any pollination taking place. I hope there are parties that look at the causes and take this seriously.”
Wat valt er te doen aan de insectensterfte?
2023-06-05 03:11:04
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