Pollinators on the edge: The European Red List of Hoverflies

Pollinators on the edge: The European Red List of Hoverflies

The European Red List of Hoverflies, which provides conservation status for European hoverfly species, was published last week. Hoverflies, the family Syrphidae, are abundant, diverse, and surprisingly handsome flies. Many species are bee or wasp mimics. Hoverflies are also the second most important group of pollinators, right after bees. Being second to bees doesn’t mean we could live without them – hoverflies visit a different spectrum of flowers, fly longer distances, and thrive in different climates and habitats than bees, all of which make them irreplaceable.

In the published Red List, 55 scientists and experts estimate that as many as 314 hoverfly species (about 37%) are threatened with extinction in Europe, and an additional 61 species (about 7%) are near threatened. Only slightly above half of all species are considered of least concern (469 species, 52.7%). About 5% of species are data deficient (DD), meaning we lack the data for assessing them.

For hoverfly conservation, it is important to consider the diverse life strategies of hoverfly species, whose larvae live in a wide range of habitats and have varied diets. Adult hoverflies feed on nectar and pollen, but their larvae can be aphid predators, feed on dead organic matter in wet habitats, eat plants, be associated with old trees, or live in an ant nest. One of the reasons why hoverflies are endangered could be the loss of larvae habitats, especially of old trees and wet habitats.

This assessment also answers the “Now what?” question, what to do with this long list of endangered species? In the accompanying document, authors propose grouping endangered species by their natural history and planning specific population recovery activities for each group. The emphasis is on the conservation of old, veteran trees through changes in forest management, protection and restoration of wet habitats, and promotion of sustainable agriculture – activities that will help many other groups of organisms and the environment.

In addition, hoverflies also still need a good amount of PR, as they are not as well-known and popular as bees or butterflies. If you want to learn more about these beautiful and important flies, we recommend the IUCN Hoverfly Specialist Group. And tell one person today – Have you heard about hoverflies?


Vujić, A., Gilbert, F., Flinn, G., Englefield, E., Ferreira, C.C., Varga, Z., Eggert, F., Woolcock, S., Böhm, M., Mergy, R., Ssymank, A., van Steenis, W., Aracil, A., Földesi, R., Grković, A., Mazanek, L, Nedeljković, Z., Pennards, G.W.A., Pérez, C., Radenković, S., Ricarte, A., Rojo, S., Ståhls, G., van der Ent, L.-J., van Steenis, J., Barkalov, A., Campoy, A., Janković, M., Likov, L., Lillo, I., Mengual, X., Milić, D., Miličić, M., Nielsen, T., Popov, G., Romig, T., Šebić, A., Speight, M., Tot, T., van Eck, A., Veselić, S., Andric, A., Bowles, P., De Groot, M., Marcos-García, M.A., Hadrava, J., Lair, X. , Malidžan, S., Nève, G., Obreht Vidakovic, D., Popov, S., Smit, J.T., Van De Meutter, F., Veličković, N. and Vrba J. (2022). Pollinators on the edge: our European hoverflies. The European Red List of Hoverflies. Brussels, Belgium: European Commission.

Sculptured resin bee

Sculptured resin bee

A new study is published about alien bee species that is spreading across Europe

The sculptured resin bee, Megachile sculpturalis, is a potentially invasive alien pollinator in Europe. Native in East Asia. it was unintentionally introduced to North America in the nineties, and France in 2008, from where it rapidly spread across Europe. It has been present in Croatia since 2018.

The sculptured resin bee is a solitary species. Females nest in existing cavities and cracks in dead wood, similar to our native carpenter bees (genus Xylocopa). They collect plant resins to seal their nests, which is how they got their common name. They are active in the summer and collect pollen and nectar from various plant species. In Europe, they are mostly found on non-native ornamentals, such as the Japanese pagoda tree (Styphnolobium japonica) and Chinese wisteria (Wisteria sinensis). The sculptured resin bee is easy to recognize – large (larger than a honeybee), with a black head and abdomen, a light brown, hairy thorax, and opaque wings.

We still don’t have enough data to know if this species has a negative impact on our native pollinators. However, there is some evidence of competition for nesting resources and aggressive behavior, so we consider it potentially invasive. That is why it is important to continue research and monitoring.

The newly published research, in which we had a chance to participate, reports the spread of the sculptured resin bee across Southeast Europe and new data about the species’ ecology. In addition to field research by an international team of scientists, this work also involved citizen scientists. The sculptured resin bee is easy to recognize, favors populated places, and is not dangerous for humans. All of this makes it a good candidate for citizen science – a practice in which citizens collect data used for scientific research.

Interestingly, in this study, the data collected by citizen scientists covered a five times bigger geographical area than the targeted research of scientists, which highlights the advantages of this approach for monitoring. We emphasize the benefits of collaboration of citizens and formal scientists and the importance of international collaboration for monitoring. You can read the published work here.

Want to get involved? If you see the sculptured resin bee, let us know! Report your observation through the app Invasive Species in Croatia or through the contact form on this website. The report should include the location and date of observation, and a photo or video of the species. Your data will contribute to the monitoring of the sculptured resin bee in Europe and to our understanding of its impact on our native ecosystems.

Photos: J. Bila Dubaić

Pollinator city

Pollinator city

One of the ways we can help wild pollinators is by changing the mowing regime of urban green spaces

We like it when nature is tidy. Shortly cut, monotonous lawns, parks that look like football or golf courses instead of flowering meadows, became the standard in city parks. What we like to call an urban green oasis is, from a biodiversity standpoint, a green desert.

Cities are, in the first place, spaces where a majority of the human population lives, and their primary function is not to maintain biodiversity. City parks also have an important socio-cultural role. However, with increasing urbanization and numerous environmental pressures, such as pollution and climate change, it is becoming clear that the greening of cities is essential for a sustainable future and human health. Green cities are also becoming a clearly defined goal of global and European policies.

Wild pollinators are particularly interesting in this regard. Studies have shown that cities can support diverse wild pollinator populations. Pollinator diversity is sometimes, unexpectedly, higher in cities than in surrounding areas, especially if those areas are affected by agriculture. This is especially true for bees, but with careful management of urban parks, we can improve habitats for other groups of pollinating insects as well, such as hoverflies, butterflies, and moths. Cities can indeed become green oases, but they need minor changes in the way they manage their green spaces: primarily reducing the use of chemical pesticides and changes in the mowing regime.

The standard of a neat lawn is achieved by frequent, intensive mowing, which is scientifically proven awful for the environment. Frequent mowing warms and dries the soil, reduces the diversity and biomass of plants and animals, and prevents the flowering of plants that are an important source of pollen and nectar for pollinators. The moment the lawnmower passes through the park, pollinators, and many other animals are suddenly left without food and shelter. Research in European and American cities shows that a reduced mowing regime is environmentally and economically beneficial – leading to increased diversity of animal and plant species, reduced greenhouse gas emissions, and financial savings of as much as 36%.

For all of those reasons, we decided to test pollinator-friendly management practices in the city of Zagreb. Our collaborators for these activities are Public Institution Maksimir for the management of protected areas of the city of Zagreb, Zrinjevac Subsidiary, and Croatian Museum of Natural History, and we have the support from the City of Zagreb and the City institute for cultural and natural heritage conservation. We defined test plots in three city parks: Maksimir, Ribnjak, and Rokov perivoj. In those parks we will establish the so-called short-flowering meadow – an area mowed only 4 times a year, and a long-flowering meadow – a strip along the edge of the lawn or a larger area mowed only once a year. This is an example of a mosaic mowing regime – although all surfaces are cut, not all are cut at the same time, so at least part of the area is in bloom at all times.

This mowing regime is based on similar actions from All-Ireland Pollinator Plan, which we have adapted to our conditions. This Plan has been a huge success in Ireland, where its implementation started in 2015. For example, one of the unexpected results was an increase in the number of rare orchids, which began to flower on roadsides just a year after the reduction of the mowing regime. Ireland is a great example, but good stories can be found in other cities as well, such as the urban meadows in Berlin, the Olympic Park in London, and beyond.

In Zagreb, for a start, we expect to see more dandelions, clover, and daisies in bloom, all fantastic native plants and a good source of food for pollinators. Pilot plots are also our Cro Buzz Klima project areas, and we will continue to monitor the abundance and diversity of plants, bees, hoverflies, and butterflies, which we partially started last year. This will allow us to assess how these changes are affecting urban biodiversity and how to plan the management of the green spaces of our cities in the future.

tabla Maksimir

P.S. If you belong to the part of the population that is wary of any bugs (useful to humans or not) and you are a little scared of all this, keep in mind that the increase in insect diversity (= larger number of different species) prevents pest outbreaks (= sudden increase in abundance of one species). Greater diversity means more natural enemies and a shift towards ecological balance. It also positively impacts the populations of other, larger predators (such as swallows, blackbirds, and other birds that feed on insects).

Visiting Linz bee collection

Visiting Linz bee collection

Last week we visited the natural history museum in Linz, Austria (Biologiezentrum Linz), which holds the largest collection of bees in Europe. The collection contains about 690 thousand individual bees, properly prepared and labeled, and permanently stored in entomological¹ boxes. Insect collections are just a part of natural history collections, which also include pressed plants in the herbarium, bones or stuffed bodies of vertebrates, fossil specimens in rocks, and similar.

Why is it important to visit the collection for our project? Museum collections² are essential for correct species identifications. To identify wild bees collected during last year’s fieldwork, we first used taxonomic keys³. We then took the train to Linz – together with 6 boxes of bee samples. In Linz, we compared the bees one by one with the material from the Museum collection, which was determined and confirmed by experts, in order to validate (or correct) our identifications.

Correct species identifications are basic data for further analysis. For example, in order to compare different areas and different habitats by their species richness and composition, we need to know what species we collected. Accurately identified samples are also important for establishing our project collection.

Another reason why a visit to Linz was so useful was meeting the museum staff and their collaborators, experts with years of experience in wild bees. They steered us in the right direction for some species, corrected our mistakes in others, pointed out the literature we didn’t know about, and in general helped with their advice and encouragement.

Museum collections all over the world are important tools of scientific discovery and nature conservation, which are sometimes insufficiently recognized. Collections enable us to reconstruct historical species ranges, track population dynamics of endangered species, and analyze morphological changes of particular species over time. They enable the discovery of new species and reconstruction of the evolution of life on earth.

By comparing historical data from collections with more recent data, we can study the impact of different anthropogenic pressures, such as climate change or land-use change, on wild pollinators and other living organisms. A famous example is the use of museum collections of bird eggs to determine temporal changes in eggshell thickness due to exposure to pesticides. This research was key evidence in proving the harmfulness and banning of DDT in the 1960s. The recovery of bird populations after the ban is one of the success stories of nature conservation and an example of the importance of museum collections.

1 – Entomology is a study of insects (from the Greek word entomon – insect).

2 – Museum collection – when you visit a natural history or any other museum you see only the part that is open to visitors, which is only a very very small part of the museum collections. Specimens selected for display are usually less than 1% of the total museum collection. Keep this in mind on your next museum visit.

3 – Taxonomic keys – expert publications used to identify species of groups. They are mainly based on morphology.

Hotels for solitary bees

Hotels for solitary bees

The majority of wild bee species are solitary, which means they don’t live in colonies like honey bees or bumblebees, but alone. Although most solitary bees nest in soil, some species nest in cavities in trees, stems, and twigs. These cavity-nesting bee species will consider renting a room in a so-called bee hotel.

Bee hotels are not new. We have been using them in agriculture since the middle of the last century, to improve pollination in orchards and other crop systems. Recently, bee hotels have become more broadly popular, mostly due to media attention given to the worrisome decline of wild pollinators across Europe and North America.

Whether bee hotels can help declining pollinators will depend somewhat on the context. In complex, natural habitats wild pollinators do not lack nesting resources. Setting up a bee hotel in such places will not do any harm, but it probably won’t have much of a positive effect either. In natural habitats, bee hotels can have an educational or research role. But in anthropogenic habitats that lack complexity, such as urban or agricultural areas, nesting resources are limited, so setting up a bee hotel can have a positive impact.

If you are planning to build a hotel, you should keep in mind the other important factor for bees: the availability of food. Most small solitary bees do not forage far from the nest, up to several hundred meters. If you are setting up a bee hotel in your garden, you can improve the floral resources very easily. Dandelions, daisies, and clover are great sources of nectar and pollen, so mowing less frequently is often the best thing you can do to help the pollinators.

Bee hotels can vary in design, but most are built from narrow horizontal tunnels or tubes, closed at one end. Each of these tunnels will serve as a nest for one female solitary bee, which will build individual rooms, one after the other, along the tunnel. In each room, the bee will lay a single egg that will develop into a larva, and supply it with food – a ball of nectar and pollen. Walls between rooms are built from mud, resin, small pieces of leaves and petals, or pebbles, the building material depending on the bee species.

Making a bee hotel is simple, but you need to keep in mind a few rules. We explain these in a short leaflet, which you can find at the end of this post. We created the leaflet together with students from Section for Hymenoptera of “Biology Students Association – BIUS“. Their section studies all Hymenoptera (including bees, ants, and wasps), but their main focus are wild bees, and they have practical experience in building bee hotels. If you are a biology student interested in wild bees (or ants or wasps), get in touch with them – they plan exciting activities for when it warms up.

To keep in mind:

  • If you are ambitious, it is better to build several small hotels than one large. Big hotels attract more predators and parasites.
  • Maintenance matters. Remove the used tubes and replace them with new ones each year. Replace drilled wooden blocks every two years.
  • Meadow flowers are not the only food source for bees – many trees and shrubs are rich in pollen or nectar.

Download the Bee Hotel leaflet (in Croatian)