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ISSN 0771-5277 Phegea 51(4) 01.xii.2023: 161
The invasion of Carcharodus alceae, Brenthis daphne and Pieris mannii
(Lepidoptera: Hesperiidae, Nymphalidae & Pieridae) into western
Belgium through opportunistic data collection
Sylvain Cuvelier & Jacques Vervaeke
Abstract. The northward and westward Belgian range expansions of Carcharodus alceae (Esper, 1780) (Hesperiidae),
Brenthis daphne (Denis & Schiffermüller, 1775) (Nymphalidae) and Pieris mannii (Mayer, 1851) (Pieridae) are studied, based
on a large number of opportunistically collected species occurrences. This information has been filtered to improve the quality
of the dataset, and an analysis of this screening is presented. An overview of the range expansion and voltinism for each species
is given. Ecological species-specific requirements that potentially influence such expansions are discussed, as well as the
westward expansion of all three species.
Samenvatting. De noord- en westwaartse uitbreiding van Carcharodus alceae (Esper, 1780) (Hesperiidae), Brenthis daphne
(Denis & Schiffermüller, 1775) (Nymphalidae) en Pieris mannii (Mayer, 1851) (Pieridae) in België worden onderzocht aan de
hand van een groot aantal, opportunistisch verzamelde, observaties. Deze data zijn gefilterd om de kwaliteit van de dataset te
verhogen en hiervan is een analyse gemaakt. Een overzicht van de soortenuitbreidingen en vliegtijden wordt gegeven. We
onderzoeken de soortspecifieke, ecologische verwachtingen die de uitbreidingen kunnen beïnvloeden, met bijzondere
aandacht voor de westwaartse expansie van de drie hogervermelde soorten.
Résumé. L'expansion vers le nord et l'ouest de la Belgique de Carcharodus alceae (Esper, 1780) (Hesperiidae), Brenthis
daphne Bergsträsser, 1780 (Nymphalidae) et Pieris mannii (Mayer, 1851) (Pieridae) est étudiée sur base d'un grand nombre
d'observations, recueillies de manière opportuniste. Les données ont été filtrées pour augmenter la qualité de l'ensemble et
une analyse du jeu de données est proposée. Un aperçu des expansions et des temps de vol des espèces est donné. Nous
examinons les attentes écologiques spécifiques de chaque espèce qui peuvent influencer ces extensions de l'aire de répartition
en portant une attention particulière à l'expansion vers l'ouest des trois espèces.
Key words: Papilionoidea — Range expansion — Phenology — Opportunistic data collection — Belgium.
Cuvelier S.: Diamantstraat 4, B-8900 Ieper, Belgium. sylvain.cuvelier@telenet.be
Vervaeke J.: Oscar Seynaevelaan 13, B-8560 Gullegem, Belgium. jacques.vervaeke1@telenet.be
DOI: 10.6084/m9.figshare.24417289
Introduction
The distribution range of most butterfly species in
Northwest Europe has long since been intensively studied,
providing an excellent historical background for studies
about distribution dynamics. In the 1900s, dramatic
contractions of many species have been well
documented. This has been linked to intensive habitat loss
and subtle changes in climate, but there were also winners
that have benefited from these changes, having expanded
their range in a rapidly changing European environment.
Range expansions depend on the ability of each species to
expand its range into new habitats in fragmented
landscapes. These expansions are driven by population
growth and the ability to disperse and thrive in new areas.
Species in expansion that establish permanent
populations should not be confused with seasonal
migrants (those usually dependent on northerly spring
migration and a southerly autumn migration), i.e. a
temporary residence of a species. Researchers often link
the recent expansions to anthropogenic climate changes.
The potential expansion of the European butterflies
was modelled against climate change by Settele et al.
(2008) using UTM grid cells of 50×50 km2. This resulted in
a northward shift of the European distribution ranges of
many species. Many butterfly species with specific
microclimatic requirements can inhabit patches in these
large grid areas, and these can affect the overall
values/assessments for each grid cell making predictions
difficult (Kudrna 2013). Like all modelling studies, the
results depend on well-chosen variables to help evaluate
a realistic output. More versatile and widespread species
that have the ability to survive in a variety of habitats and
utilize different larval hostplants make this modelling
more difficult, but hostplants are an essential condition in
regard to the survival of each species.
In the Balkan peninsula, an unintuitive southward
expansion of Araschnia levana (Linnaeus, 1758) into
Greece has even been documented (Pamperis 2009, 2022)
and that does not appear to be a climate-driven
expansion. Expansions can also be driven by changes in
behaviour and life history as shown (Neu et al. 2021) by
Pieris mannii (Mayer, 1851). Small changes in the gene
pool of a species might be the cause of such a changing
habitat preference and performance (Holt 2003). Range
expansions can be inhibited by interspecific competition
(Legault et al. 2020) which can influence the rapidity and
the geographical limitations of any expansion.
Documenting range expansion potentially confirms the
relevance of these modelling programs and can influence
future studies. Describing such expansions largely
depends on the number of observations, and on the
accuracy of the recorded data that is uploaded into the
database. Online observation platforms (e.g.
Waarnemingen.be/Observations.be) or large citizen
science projects allow the opportunity for a multitude of
participants to gather and upload a large number of
opportunistic observations even when it is not the ideal
research method with a standardized protocol. The
quality of such opportunistic data collection is sensitive to
Phegea 51(4) 01.xii.2023: 162 ISSN 0771-5277
the heterogeneity of the sampling effort, in time and
space, and a basic knowledge of species identification is
essential and critical.
The recent development of a number of identification
tools based on artificial intelligence recognition has added
a degree of uncertainty (Mølgaard & Cuvelier 2021) in
regard to collating accurate records; this is especially
pertinent to those taxa with similar external
characteristics. However, Van Eupen et al. (2021)
acknowledged that the filtering of such opportunistic data
can still make a valuable contribution to ecological
research. Over several decades, the authors (Cuvelier et
al. 2007) have studied butterflies in the westernmost
province of Belgium and during the course of their surveys
have noticed an unexpected expansion of Limenitis
camilla (Linnaeus, 1764) commencing in 2004.
Additionally, recent observations of P. mannii and
Carcharodus alceae (Esper, 1780) in West Flanders
initiated a study of the westward expansion of these two
species. Coincidentally, the less rapid westwards
expansion of Brenthis daphne ([Denis & Schiffermüller],
1775) started almost simultaneously with C. alceae but at
present has not reached the province of West Flanders.
The only record of B. daphne in western Belgium relates
to a single dead specimen that was found on July 20th,
2010, in the enclave of Hainaut in West Flanders (Cuvelier
& Spruytte 2011).
Methods
All observations relating to P. mannii, C. alceae and
B. daphne were kindly provided by the online nature
observation platform, Waarnemingen.be./Observations.
be. This data cannot be reproduced without permission.
Personal observations regarding the phenology of
P. mannii and C. alceae in the western part of Belgium
were recorded by the second author and analysed.
Subsequently, the Excel data from this platform was
filtered to exclude duplicates and doubtful or erroneous
identifications. Regarding the status column, five different
levels of validation are provided:
a) approved, based on evidence;
b) approved, based on expert judgement;
c) approved based on knowledge rules – proximity;
d) not evaluable;
e) untreated.
All observations from the two first validation levels were
accepted. Observations from the last three levels were
analysed and validated or, in some cases, rejected by the
authors. Subsequently, non-validated observations were
excluded from the study.
A global analysis (Table 1) of the discordance between
the provided data and filtered data was made for each
species, as well as the judgement regarding the validation
process as presented in the Excel spreadsheet from the
forum. In preparing the phenograms, all dates were
allocated to three-thirds (decades) per month. Filtered
data of all the development stages is used to map the
annual distribution and to analyse the northerly and
westerly expansion of each species. The annual
expansions have been analysed as well as the annual
spread in northerly and westerly occurrences. Only the
filtered data of the adult butterflies were used for the
phenological analysis. In some instances, the amount of
data was inadequate to provide a meaningful outcome.
The flight times of species from West Flanders were
compared with those from the provinces of Limburg (both
in the Atlantic biogeographical region), Liège, and
Luxemburg (situated in the continental biogeographical
region). DMAP distribution mapping software was used to
create the coverage maps.
Results
1. The database: from the initial
observations to the filtered Excel version
Depending on the species (Table 1) there are major
differences when comparing the information received
with the filtered data. Duplicates of similar observation
and identification issues are present at different degrees
for the three species.
A summary for the number of rows, the number of
specimens, and the ratios per species is given in S1 where
more details are available per species.
The filtered data for the three species provides
virtually complete geographical coverage for all of
Belgium (Table 1) and reveals those areas that are more
intensively studied. In Flanders, this is linked to the
number of local volunteers, which usually relates to the
population density. This creates a heterogeneous
observer effect that needs to be taken into account when
studying the data for each species. In southern Belgium,
the known butterfly hotspots with higher entomological
diversity attract twitchers and cause another type of
observer effect.
Table 1. Comparison of the filtering to the provided Excel database, according to the levels of validation from the forum. © Cuvelier & Vervaeke.
ISSN 0771-5277 Phegea 51(4) 01.xii.2023: 163
Fig. 1. Map of Belgium depicting the filtered observations of Carcharodus
alceae, Brenthis daphne and Pieris mannii. © Cuvelier & Vervaeke.
2. Carcharodus alceae (Esper, 1780) /
Mallow skipper
(Fig. 2d)
The data from the forum included a few observations
from 1928, 1933, 2004, and 2005. In regard to the
expansion of C. alceae in Belgium, continuous annual
observations are available from 2007. The distribution
map of C. alceae (Fig. 3a) shows a different pattern to that
of the global distribution map (Fig. 1). The virtual absence
of dots in the north-eastern part of Flanders is of note. In
the adjacent areas of the Netherlands (Fig. 3b) the
situation is identical, confirming that C. alceae is, more or
less, at the limit of its actual expansion in this part of
Flanders. In Wallonia the density of dots is notably lower.
Fewer observations resulting from a smaller number of
recorders is probably the main reason for this discrepancy
and, relating to the intensity of dots in the butterfly
hotspots, one can ascertain that the species is no more
widespread than in the north of the country. The
phenology (Fig. 3c) and chronology of the annual
expansion are detailed in S2. In Fig. 3d, the evolution of
the northerly and westerly spread is provided. In 2009,
C. alceae started expanding its range into the northern
part of Belgium, and during the following years, a gradual
westerly expansion was also witnessed. In 2018 C. alceae
reached its present distribution boundaries.
3. Brenthis daphne (Denis & Schiffer-
müller, 1775) / Marbled fritillary
(Fig. 2a)
The first observations, uploaded in 2008, and
subsequent annual observations have been continuous.
The map (Fig. 4a) gives the total coverage for all
development stages. The species occurs primarily in the
provinces of Namur, Liège, and Luxemburg. In western
Wallonia and Flanders the intensity of dots is visibly lower.
Despite the lower observation intensity in Wallonia, it is
clear that at present the strongholds of B. daphne are in
the more diverse, hilly habitats of Wallonia. The
phenology (Fig. 4b) and evolution of the annual expansion
are detailed in S3. The northerly and westerly spread of
the expansion in Belgium is given for each year (Fig. 4c). In
2009, B. daphne started to expand its range in a slow, but
continuous, northerly direction, while the western limit of
its range barely changed until 2017. In the following years,
a slow westerly expansion was documented but the
number of observations still remained low. In 2018,
B. daphne reached the northern Belgian limits. However,
the species has not as yet (end of 2022) expanded its
range to the western part of the province of Hainaut and
West Flanders.
Fig. 2a. Brenthis daphne, Börfink Hunsrück-Hochwald National Park (D), 23.vii.2019. © J. Vervaeke.
Fig. 2b. Pieris mannii ♂, Gullegem (B), 12.ix.2021. © J. Vervaeke.
Fig. 2c. Pieris mannii ♀, Gullegem (B), 12.ix.2021. © J. Vervaeke.
Fig. 2d. Carcharodus alceae ♀, Ieper (B) 21.viii.2022. © S. Cuvelier.
Phegea 51(4) 01.xii.2023: 164 ISSN 0771-5277
Fig. 3a. Distribution map of Carcharodus alceae in Belgium including all filtered observations. © Cuvelier & Vervaeke.
Fig. 3b. Map of the adjacent Dutch distribution of Carcharodus alceae. Source: Waarneming.nl.
Fig. 3c. Phenogram (2007–
2022) of Carcharodus alceae
imagos.
© Cuvelier & Vervaeke.
Fig. 3d. Evolution of the
annual northerly and
westerly spread of
Carcharodus alceae from
2008–2022.
© Cuvelier & Vervaeke.
ISSN 0771-5277 Phegea 51(4) 01.xii.2023: 165
Fig. 4a. Distribution of Brenthis daphne in Belgium including all filtered observations. © Cuvelier & Vervaeke.
Fig. 4b. Phenogram (2008–2022) of Brenthis daphne imagos. © Cuvelier & Vervaeke.
Fig. 4c. Evolution of the
annual northerly and
westerly spread of Brenthis
daphne from 2008–2022.
© Cuvelier & Vervaeke.
4. Pieris mannii (Mayer, 1851) /
Southern small white
(Fig. 2b, c)
The first Belgian observations to be uploaded into the
forum were made during the summer of 2016. The first
specimen was recorded in the province of Luxemburg, and
soon after several additional sightings were made in
Voeren, an exclave of Flanders. Logically, it appears that
P. mannii reached Belgium from the East. The Rhine valley
has been mentioned as the main route for this northern
expansion, and from there P. mannii appears to have
extended its range in a westerly and easterly direction
(Vantieghem 2018). Since 2016, the species has regularly
been recorded in Belgium, extending its range westwards,
with an extensive shift witnessed as from 2018 (see S4).
However, it is interesting to note that the total number of
observations made during 2022 fell back to the level
witnessed in 2020 (Fig. 5b). Surprisingly, the summer in
2022 was hotter and drier than in 2021, and as P. mannii
originates from the Mediterranean region (inhabiting
warm, dry rocky slopes with scattered bushes), one would
assume that this would favour further expansions in the
surrogate habitats in Belgium (rock gardens with Iberis
sempervirens and sites with a warm microclimate where
Brassicaceae are available). Fig. 5a shows a different
pattern to that of the global distribution map (Fig. 1). The
density of observations in Flanders is very evident. The
lower density in the western part of Flanders reflects the
later westward invasion. The earliest observations in West
Flanders were recorded during 2020; however, data
suggest that the sparsely populated Polders area is not
suitable for the expansion of the species. In Wallonia the
density is visibly low, this possibly relates to the lower
observer effect and hence observations. Even in the
butterfly hotspots in Wallonia the number of recorded
sightings is low, suggesting that the species is not common
in these areas. Compared to the current status of C. alceae
and B. daphne, it appears that the northern expansion of
P. mannii is not limited to Belgium. The phenology (Fig. 5c)
and evolution of the annual expansion are detailed in S4.
Phegea 51(4) 01.xii.2023: 166 ISSN 0771-5277
Fig. 5a. Distribution of Pieris mannii in Belgium including all filtered observations. © Cuvelier & Vervaeke.
Fig. 5b. Pieris mannii, annual number of observations in Belgium including all development stages. © Cuvelier & Vervaeke.
Fig. 5c. Phenogram (2016–
2022) of Pieris mannii
imagos.
© Cuvelier & Vervaeke.
Fig. 5d. Evolution of the
annual northerly and
westerly spread of Pieris
mannii from 2016–2022.
© Cuvelier & Vervaeke.
ISSN 0771-5277 Phegea 51(4) 01.xii.2023: 167
Pieris mannii is on the wing from the second decade of
March until the end of October in a succession of broods,
approximately one month longer than C. alceae, and
about five months longer than B. daphne. There are three
peaks in the phenogram suggesting three annual
generations with a large overlap between them. The
analysis of the phenograms from separate years (Fig. 9b)
confirms this impression. The northerly and westerly
spread of the expansion in Belgium is given annually (Fig.
5d). P. mannii has gradually increased its range in a
northerly and westerly direction, but its western
expansion has clearly been more rapid than that
witnessed by the other two species. By 2020, P. mannii
had already reached West-Flanders in Kortrijk, and the
first coastal observation, from the area of Knokke, was
uploaded onto the forum during the same year. By 2021,
the species has advanced its range along most of the
Belgian coastline. Discussion
Filtering data from the online observation forum, to
avoid duplicates and misidentifications, was work-
intensive, but in so doing provided a large number of
accurate observations for the three aforementioned
species. As expected, filtering did not influence the
heterogeneity of the spatial sampling effort. The intensity
of the dots in any given area is dependent on the observer
effect, which is obviously greater in the more densely
populated areas of Belgium and in the more frequently
visited butterfly hotspots. The intensity of the dots in the
distribution map of B. daphne (Fig. 5a) in the southeast of
Wallonia contradicts that of C. alceae (Fig. 3a) and
P. mannii (Fig. 5a) which have their highest number of
observations in Flanders. One can assume that this is due
to the slower expansion (S4) of B. daphne. The disparities
regarding the intensity of the dots on the map for
C. alceae (Fig. 3a), which appears to be virtually absent in
northeast Flanders, and for P. mannii (Fig. 5a), with lower
coverage of dots in the western part of Flanders, are
noteworthy.
Pieris mannii only started its westward expansion in
2018 (see S4) reaching West-Flanders, for the first time, in
2020. This disparity regarding the intense concentration
of dots might well reflect the timing of the occurrence of
the expansion. One should note that the distribution map
is an ongoing process, and observations for the western
part of Flanders will be added continually. The garden
experience by the second author (Fig. 10) supports the
hypothesis that predicts the numbers, and spread, of
observations in West Flanders will probably mimic the
expansion witnessed in other parts of Flanders, except
possibly the sparsely populated Polders area in West
Flanders. The northern and western limits of the
distribution of C. alceae (Fig. 3a, S2) have been more or
less stable since 2018. We can assume that the intensity
of this coverage map is no longer subject to a recent
expansion as it is for P. mannii. The absence of dots in the
north-eastern part of Flanders is not due to a lack in
observations. It shows the actual distribution limit of
C. alceae, and this is confirmed when we compare it to the
adjacent distribution area of the species in the
Netherlands (Fig. 3b). Additionally, the filtered data can be
used to plot the annual northerly (Fig. 6a) and westerly
(Fig. 6b) shift of all three species, thus giving a visual
representation of the speed of their expansions.
B. daphne and, to a lesser extent, C. alceae, have periods
of unpredictable up and down shifts. This is not the case
for P. mannii which shows a markedly westward shift.
Such a visualization is very sensitive but at the same time
it depends on a single specimen, a potential outlier.
Comparing the percentual evolution of the annual
northerly and westerly expansions of the three species
into Belgium (Fig. 3d, Fig. 4c, Fig. 5d) might be a stronger
marker for the northward (Fig. 7a) and westward (Fig. 7b)
expansion. Additionally, by analysing the annual data,
based on the initial observations of all three species, we
have a better indicator of the rapid northward and
westward expansion of the three species (Fig. 8). At the
start of the expansions into Belgium, the northerly shift of
all three species was more noticeable, compared to the
westerly shift.
Fig. 6a. Annual northerly shift for the most northern observation. © Cuvelier & Vervaeke.
Fig. 6b. Annual westerly shift for the most western observation. © Cuvelier & Vervaeke.
→ : Carcharodus alceae; → : Pieris mannii; → : Brenthis daphne.
Phegea 51(4) 01.xii.2023: 168 ISSN 0771-5277
Fig. 7a. Percentual evolution of the annual south-north range expansion of Carcharodus alceae, Brenthis daphne and Pieris mannii.
© Cuvelier & Vervaeke.
Fig. 7b. Percentual evolution of the annual east-west range expansion of Carcharodus alceae, Brenthis daphne and Pieris mannii.
© Cuvelier & Vervaeke.
Fig. 8. Percentual evolution
of the annual south-north
and east-west range
expansion of Carcharodus
alceae, Brenthis daphne and
Pieris mannii, modelled on
the year of their first
appearance. © Cuvelier &
Vervaeke.
Fig. 9a. Annual phenogram
of Pieris mannii. © Cuvelier
& Vervaeke.
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Fig. 9b. Phenogram (2016–
2022) of Pieris mannii in
four Belgian provinces.
Full lines: Atlantic biogeo-
graphical region, dashed
lines: continental biogeo-
graphical region.
© Cuvelier & Vervaeke.
Fig. 10. Phenogram of adult
Pieris mannii observations
(2021–2022) in the garden
of Jacques Vervaeke; m:
adult males; f: adult
females; black line: all
imagos. © Cuvelier &
Vervaeke)
Fig. 11. Phenogram (2007–
2022) of Carcharodus
alceae in four Belgian
provinces. Full lines:
Atlantic biogeographical
region, dashed lines:
continental biogeogra-
phical region. © Cuvelier &
Vervaeke.
Phegea 51(4) 01.xii.2023: 170 ISSN 0771-5277
Bearing in mind the heterogeneity of the data,
C. alceae, B. daphne and P. mannii show different patterns
of northerly and westerly expansion. This may be the
result of different species-specific variables:
a) hostplant specialization (monophagous-polypha-
gous);
b) habitat specialization and preferences (specialist to
generalist);
c) dispersion ability (low to high);
d) differences in voltinism (number of annual genera-
tions).
Referring to the provisional checklist of European
butterfly larval foodplants (Clarke 2022), none of the
three studied species is monophagous. In increasing order
of number of foodplants, B. daphne utilises nine food-
plants from two genera (Rubus and one Filipendula);
C. alceae accepts seventeen foodplants from four genera
and P. mannii is credited with using twenty-three food-
plants from fourteen different genera. The availability and
wider distribution of the main food plants have not been
studied in depth; they do not appear to be limiting factors
regarding the expansion of the three species in Belgium.
None of the studied species are habitat specialists, despite
having different habitat preferences. Estimating the
dispersion ability of each species is difficult without lab
work, but being involved in large expansions it appears
that all three species are quite capable of continued
dispersal. There is a major difference in the phenology of
the three species. B. daphne has a single generation
(Fig. 5b) from early June to early August (7 decades). By
contrast, C. alceae (Fig. 3c) and P. mannii (Fig. 5c) are
polyvoltine. The flight time of C. alceae stretches from the
second decade of April until the end of September (17
decades), compared to P. mannii which is on the wing
from the end of March till the end of October (22
decades). As voltinism may be an important factor, and
because global phenograms are difficult to interpret (Bink
& Moenen 2015), more detailed analyses are presented
for both P. mannii (Figs 9a–b, 10) and C. alceae (Fig. 11).
By comparing the annual phenograms (Fig. 9a), variations
that have occurred in extreme years can be clearly seen,
and not in the multiyear phenogram (Fig. 5c). Fig. 9a
illustrates the need to show a minimum number of
observations to visualize peaks and/or shifts in optimum
flight periods when comparing annual flight patterns. In
Belgium, the summer of 2021 was one of the wettest since
records began in 1833, with 2020 and 2022 being
extremely dry, hot, and sunny years. These extreme
conditions resulted in a one-decade shift of the July peak
emergence and a two-decade shift of the September peak
emergence for P. mannii.
As Belgium has two different biogeographical regions,
analyses of the flight times of P. mannii (Fig. 9b) and
C. alceae (Fig. 11) are presented for two provinces in the
Atlantic biogeographical region (West Flanders and
Limburg) and for two provinces in the continental
biogeographical region (Liège and Luxemburg). There are
no conclusive differences in the phenograms for C. alceae,
and no obvious disparities regarding the voltinism for the
two biogeographical regions where P. mannii is present.
Both graphs (Figs 9b, 11) confirm that below a quantity
threshold, the interpretation of phenograms is
insignificant.
Additionally, an analysis (Fig. 10) is presented for a
single locality in West Flanders, the garden of the second
author, from where daily observations of P. mannii were
recorded. The species was noted for the first time in
August 2021, and specimens of both sexes were observed
in the second half of September during peak emergence.
In April 2022, small numbers of the first generation were
recorded, followed by three peaks (further broods/
generations), in June, mid-August, and September, with a
discernible overlap between these peaks.
For the potentially important variable of voltinism, it
appears better to interpret the expansion using the
annual number of decades to avoid the pitfall of a number
of generations in what is probably an opportunistic
overlapping continuum in the summer months until the
weather conditions become too bad for a given species.
The speed of the expansions of P. mannii, C. alceae and
B. daphne correlates well with the annual number of
decades in the phenograms. Major factors limiting the
protraction, or advancement, of a further northward
expansion may depend on future climatic conditions and
the sustainability of existing habitats. Limiting factors
affecting the continued westward expansion of B. daphne
may depend on the availability of suitable habitats, and
the lack of corridors to expand its range to suitable areas
in western Belgium.
Acknowledgements
We thank Waarnemingen.be/Observations.be, the
website for nature information of Natuurpunt/Natagora
and Stichting Natuurinformatie for kindly providing their
data. We also express our special gratitude to Martin
Gascoigne-Pees for his suggestions and linguistic
corrections and thank Stef Spruytte for proofreading the
abstract.
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https://doi.org/10.3897/nl.45.72017
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Supplementary material
S1. Analysis of the database before and after filtering.
Zie — http://www.phegea.org/Phegea/Appendices/Phegea51-4_S1.pdf 761 KB
S2. Carcharodus alceae data.
Zie — http://www.phegea.org/Phegea/Appendices/Phegea51-4_S2.pdf 1.253 KB
S3. Brenthis daphne data.
Zie — http://www.phegea.org/Phegea/Appendices/Phegea51-4_S3.pdf 3.174 KB
S4. Pieris mannii data.
Zie — http://www.phegea.org/Phegea/Appendices/Phegea51-4_S4.pdf 2.518 KB
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Submitted: 21 January 2023
Accepted: 29 May 2023
