There are still 707 wild bee species in Austria. Wild bee expert Heinz Wiesbauer warns in the new edition of his book “Wild Bees” that the diversity of these insects, which are extremely important for pollination of plants, is “strongly endangered”. In addition to the massive loss of habitats, intensive land management and the use of pesticides, climate change is “extremely difficult” for wild bees.
In the past decades, 37 wild bee species have become extinct in Austria. If the criteria of the Red List were used, around half of all species would be endangered in some way, emphasized the landscape ecologist and planner, who published the first edition of his more than 500-page, richly illustrated work on this Hymenoptera order in 2017. While the new spread of species is quite easy to understand, due to the lack of systematic surveys, “the disappearance of species is hardly noticed. Populations are getting smaller and smaller and then suddenly disappear,” said Wiesbauer to the APA.
Climate change is partly responsible for this. With higher biodiversity in southern countries, one might think that most species could benefit from a warmer climate. However, the opposite is true – for different reasons for alpine and lowland species.
The mountain species are facing a projected temperature increase by the end of the century, equivalent to a 300 meter difference in altitude. But the bee species that are widespread above the tree line can hardly move upwards, since the areas towards the summit are getting smaller and smaller. This affects the alpine bumblebee (Bombus alpinus), for example, which, according to Wiesbauer, currently only occurs at altitudes over 2,200 meters. “If the lower limit of the habitat shifts from 2,200 to 2,500 meters above sea level, the area of alpine and high alpine biotopes in the Alps will decrease by 50 percent,” Wiesbauer calculated using GIS grid cell evaluations for the entire Alpine region.
In the lowlands, due to rising temperatures, certain plants are increasingly flowering at a different time than the wild bee species that are specialized in them hatch and are active. Due to the heat stress, flowers often do not develop properly, which limits the pollen and nectar supply for the bees. Because the scabious flowers usually dry up in early summer, the stocks of the specialized trouser bee (Dasypoda argentata) have plummeted and are probably already extinct in Austria, says Wiesbauer.
Extreme heat also forces the bees to take longer breaks over midday, which reduces the time for nest building and food storage. The increasing distance between the nesting site and forage plants due to the constantly decreasing supply of flowers also poses problems for the wild bees, which are usually site-loyal. This is exacerbated by the increasing competition from honey bees due to the boom in beekeeping in recent years.
Of course, there are also beneficiaries of the higher temperatures and certain species can expand their range or increase their numbers. “However, we are getting common species with it, while at the same time we are losing highly specialized species,” Wiesbauer cannot resist a dig at the insect study commissioned by the Ministry of Agriculture presented at the beginning of the year. This had highlighted the “overall predominantly beneficial effects on species richness and stocks of the examined insect groups” due to the climatic changes in Austria in recent years, which not only caused Wiesbauer to shake his head.
In his book, which also contains 510 portraits of species, the expert also gives numerous tips on how to promote wild bees through a diverse and continuous supply of flowers and suitable nesting sites – “you can achieve a lot with simple measures”. For example, he doesn’t understand “that every year at the beginning of May every embankment in Austria from Lake Constance to Lake Neusiedl is mowed”. Smaller and more differentiated pruning could improve the supply of flowers and thus the food supply for the wild bees. Steep walls, unpaved dirt roads, even gaps in the lawn would offer nesting opportunities. And even in a well-groomed garden you can offer breeding places with a few old pith stems stuck in the lawn.
(SERVICE – Heinz Wiesbauer: “Wild Bees – Biology, Habitat Dynamics and Endangerment”, Verlag Ulmer, 528 pages, 56.50 euros. Book presentation and lecture: March 15, 6:30 p.m., Natural History Museum Vienna)