The butterfly: interview with Wout Geudens
Photo: Karel De Blick
As its name suggests, the heath butterfly is a species that likes to linger in the relatively open heath and dune landscapes of Grenspark Kalmthoutse Heide. Yet this heat-loving butterfly has been struggling for several years. The heath butterfly, along with other vulnerable species, suffers from all kinds of changes, such as extreme weather conditions and changes in habitat. Monitoring this vulnerable butterfly is not only important to continue protecting the species. After all, the population also indicates the state of the habitat in which the butterfly lives.
Wout Geudens is a Master's student in Biology at the University of Antwerp. Last summer, he completed his habitat butterfly internship under the supervision of Rudi Delvaux. This resulted in an interesting internship report. We asked Wout some questions about the moorhen butterfly and his findings in the Grenspark.
How do you recognise the heath butterfly?
The heath butterfly is a butterfly of about 5-6 cm and can be recognised by the brown top of the wing, with 2 eye-spots on the forewing, and 1 on the hindwing. The underside of the forewing is light orange and has 2 eye spots, and on the underside of the hindwing you can see a kind of marble pattern. These patterns make it blend well into its surroundings, and sometimes make it difficult to spot.
What are the ideal living conditions for this butterfly?
As its name suggests, the heath butterfly is mainly found in heathland areas, but also near drifting dunes and coastal dunes. A good habitat for a heath butterfly has a number of characteristics. First of all, they naturally need nectar plants (e.g. heather), but open sandy plains are also important for the butterfly. These sandy plains are mainly used by the males who display territorial behaviour there. The presence of some trees is also important, as they can use these to find some coolness, or as protection from the wind. A final feature is the presence of patches of dry grassland. In these areas, eggs are often laid, and caterpillars develop. So, as you can see, the Kalmthoutse heath is the ideal place for this butterfly to thrive.
How is the heath butterfly monitored in Grenspark Kalmthoutse Heide?
The grenspark mainly uses volunteers who make observations in the field. Over the past two summers, there has also been a master's student from the University of Antwerp who has carried out extra counts during the month of August, helping to process the observations made by the volunteers and looking at how the moorhen butterfly is doing.
Why is it important to monitor this butterfly?
First of all, the heath butterfly is classified as 'endangered' on the IUCN Red List. Of course, this is not the only reason for protection. Indeed, the heath butterfly is also an important indicator species. Its presence in certain habitat types such as dunes or heathlands, for example, gives a good indication of the habitat quality of these areas. The heath butterfly is also very important in the pollination of nectar plants such as scrub heath and heath. Moreover, its larvae have an important role as a food source for insect-eating insects such as the parasitic wasp. So by monitoring the heath butterfly, we can not only see how this important species is doing, but also get an indication of how the habitat it lives in is doing.
What are your findings after your research?
During my research, one of the things I looked at was the population trend of the heath butterfly since 2016. A real trend cannot yet be observed, we do see that the population is fairly constant. The constant is already a good sign that the heath butterfly is not declining enormously. Compared to the previous year, there was already an increase, from an average of 1.62 sightings per day, to 5.58 sightings per day! What I have noticed is that climate has a big impact on the population. Years when there was a big heatwave in the summer, like the summer of 2020, there were a lot fewer moorland butterflies than years when we had a relatively milder summer with more rainfall, like the summer of 2021. This shows that the butterfly is sensitive to these kinds of changes and should certainly keep us alert for the future. With the changes in climate, these extreme weather events will become more frequent, and the population size may fluctuate even more. Therefore, it is important that we continue to monitor the heath butterfly to see how they respond, and we can take appropriate measures to protect our butterfly.
Want to read more about the heivlinder? You can find Wout's internship report here.