STATUS OF ENDANGERED GRAPHODERUS BILINEATUS IN SLOVENIA
WITH PROPOSAL OF URGENT CONSERVATION MEASURES 
Špela Ambrožič ErgAvEr1, Andrej KAplA1, Al vrEzEc1,2, Urška rAtAjc1
1 National institute of biology, večna pot 111, Si-1000 ljubljana, Slovenia
2 prirodoslovni muzej Slovenije, prešernova 20, Si-1000 ljubljana, Slovenia
e-mail: spela.ambrozicergaver@nib.si, urska.ratajc@nib.si, 
andrej.kapla@nib.si, al.vrezec@nib.si
Abstract – After the only historical record for Graphoderus bilineatus (De geer,
1774) in Slovenia from rače, from 1936, the species was rediscovered in 2011 in a
gravel pit in Spodnje Krapje by the mura river. the systematic large-scale survey of
Graphoderus bilineatus in Slovenia took place between 2008 and 2020 and the
species was found only at two locations by the mura river. in 2017 and 2020, the
species was found in murska šuma near the border with croatia and Hungary, but its
occurrence was not confirmed any more in Spodnje Krapje. the current protection
measures are not sufficient for effective long-term conservation of the relict
Graphoderus bilineatus population in Slovenia, which is on the brink of extinction
and urgently needs a detailed action plan.
KEy worDS: endangered species, Natura 2000, diving beetles, Dytiscinae
Izvleček – StAtUS ogrožENEgA ovrAtNiŠKEgA plAvAčA
GRAPHODERUS BILINEATUS v SlovENiji S prEDlogom NUjNiH
vArStvENiH UKrEpov
v Sloveniji je bil za ovratniškega plavača Graphoderus bilineatus (De geer, 1774)
znan le en zgodovinski podatek iz rač iz leta 1936, vrsta pa je bila ponovno odkrita v
gramoznici Spodnje Krapje ob reki muri leta 2011. Sistematična vzorčenja med letoma
2008 in 2020 so vrsto potrdila le na dveh lokacijah v Sloveniji. v letih 2017 in 2020 je
bilo potrjeno še drugo najdišče, tokrat v murski šumi, blizu meje s Hrvaško in madžar-
sko, medtem ko prisotnost vrste v Spodnjem Krapju ni bila več potrjena. trenutni var-
stveni ukrepi za dolgoročno ohranjanje vrste v Sloveniji ne zadostujejo, saj je ovratniški
plavač v Sloveniji na robu izumrtja, zato je nujen podroben akcijski načrt.
KljUčNE bESEDE: ogrožene vrste, Natura 2000, kozaki, Dytiscinae
189
ACTA ENTOMOLOGICA SLOVENICA
LJUBLJANA, DECEMBER 2021     Vol. 29, øt. 2: 189–199
Introduction
Graphoderus bilineatus (De geer, 1774) is a palaearctic species (boukal et al.
2007), distributed from France to Siberia and from Scandinavia to italy and romania
(Foster 1996). the populations towards northeast (lundkvist et al. 2002, Kalninš
2006, przewoźny et al. 2014, Kolar & boukal 2020) and in Southern Europe (turić
et al. 2021) are quite stable, but in general the species is rare and with a patchy occur-
rence (Foster 1996, Hendrich & balke 2000, 2005, iversen et al. 2013). it is declining
in some countries in central Europe (cuppen et al. 2006, Hendrich & balke 2005)
and is considered extinct in some countries in western Europe, e.g. belgium (Scheers
2015) and the United Kingdom (Foster 1996). it is one of the two species of diving
beetles listed in the Annex ii of Habitat Directive (council Directive 92/43/EEc).
in general, it is an eurytopic and acidophilic species (Koch 1989) that lives in per-
manent, unshaded, stagnant waters with a sandy or peat bottom (cuppen et al. 2006).
Hendrich and balke (2000) reported the species from shaded standing waters with
clear water, in forest bogs, and even in gravel pits. in southern Europe, in croatia, the
species was found mostly on floodplains, in oxbow lakes and canals with standing
water and medium-dense vegetation (temunović et al. 2011). 
in Slovenia the species is considered rare and endangered (Ambrožič et al. 2015a).
before 1950, there was only one known record from Slovenia. A single specimen is
stored in the central collection of beetles of Slovenia in the Slovenian museum of
Natural History, was collected in 1936 by josef peyer in the area of rače near maribor
(Drovenik & pirnat 2003). After 75 years the species was rediscovered in Slovenia in
2011 at the location of Spodnje Krapje by the mura river (Ambrožič et al. 2015a).
Following the rediscovery a systematic species survey has taken place in order to
reveal species status, distribution and vulnerability in Slovenia.
Materials and methods
the systematic surveys of Graphoderus bilineatus in Slovenia took place between
2008 and 2020 (vrezec et al. 2008, 2011, 2012, 2017a, 2017b, 2020, Ambrožič et al.
2014, 2015a, 2015b). Altogether, 268 sites were sampled using two methodological
approaches, bottle trap and net sampling (vrezec et al. 2011). in the bottle traps (see
Ambrožič et al. 2015a for details), we used various baits (canned cat food, pieces of
trout) as attractants. the trap was sunk to the bottom of the water body among vege-
tation. we set 10 to 20 traps at each location. Sampling lasted from one to two nights.
with net sampling we sampled between aquatic vegetation or along the bottom by
counting two to five swings at ten to thirteen microlocations in the water body and
recording the catch for each microlocation (Koese & cuppen 2006, Kalman et al.
2008). we sampled mainly smaller water bodies that were overgrown with aquatic
and riparian vegetation. identification to species level was performed in the laboratory
(Freude et al. 1971, Friday 1988, Hájek 2009).
Acta entomologica slovenica, 29 (2), 2021
190
All sampling of protected species was performed with the licence of the Environ-
mental Agency of the republic of Slovenia No. 35601-150 / 2006-6, No. 35601-
75/2012-8 and No. 35601-40/2017-4) issued to the National institute of biology. 
Results and discussion
in the 12-year period we sampled 268 sites altogether, while Graphoderus bilineatus
was found in only two locations (0.7%) in Slovenia (Figure 1). At Spodnje Krapje lo-
cation the species was found at two sampling events in 2011 (Ambrožič et al. 2015a),
but afterwards the species was not found again although the site was regularly sampled
(13 surveys in seven different years in the period 2012-2020). However, a second lo-
cation for this species was confirmed, in the lower part of the mura region, near the
border with croatia and Hungary in 2017 (12. 5. 2017, leg. Špela Ambrožič Ergaver,
coll. vrezec) and 2020 (21. 5. 2020, leg. Špela Ambrožič Ergaver, Urška ratajc,
Øpela Ambroæiœ Ergaver, Andrej Kapla, Al Vrezec, Urøka Ratajc: Status of endangered Graphoderus bilineatus in Slovenia
191
Figure 1: map of the historical (before 1950, blue dot) and recent (after 2010, red
dots) records of Graphoderus bilineatus in Slovenia. the systematic surveys of the
species in Slovenia took place between 2008 and 2020 using two sampling methods
on 268 sampling sites (yellow dots). 
Slika 1: Karta zgodovinske (pred letom 1950, modra pika) in recentne razširjenosti
(po letu 2010, rdeči piki) ovratniškega plavača Graphoderus bilineatus v Sloveniji.
Sistematični popisi so potekali med letoma 2008 in 2020 z dvema metodama vzorčenja
na 268 vzorčnh mestih (rumene pike).
matic gabor, coll. vrezec). A total of two individuals were caught in the traps at črni
jarek in the area of murska šuma in the old riverbed of the ledava river (Figure 1).
our findings indicate great rarity and vulnerability of the Graphoderus bilineatus
population in Slovenia. the only known recent location for the species is in the mura
river basin, which is probably the last area where this species survived in Slovenia,
since analysis showed that it had disappeared from the Drava river basin with 90%
probability (ratajc 2017). main habitats for this species in Slovenia are oxbows,
abandoned gravel pits and old riverbeds. it is difficult to speculate about specific
habitat requirements of the species here, however, the two recent locations both have
clear water and a substantial shallow water area with rich riparian vegetation. we
have not detected any major changes to habitat quality at Spodnje Krapje (Figure 2)
in terms of water chemistry or aquatic vegetation. only certain anthropogenic distur-
bances were noticed (e.g. logging and an increase in non-native fish abundances) and
the species had apparently disappeared from this location. Graphoderus bilineatus
Acta entomologica slovenica, 29 (2), 2021
192
Figure 2: An abandoned gravel pit in the Siget gravel system, Spodnje Krapje by
the river mura, in which Graphoderus bilineatus was first rediscovered in Slovenia
in 2011, but its occurrence was not confirmed after 2011 (photo: ivan Ergaver). 
Slika 2: opuščena gramoznica v sistemu Siget, Spodnje Krapje ob reki muri, v
kateri smo leta 2011 v Sloveniji prvič odkrili ovratniškega plavača Graphoderus
bilineatus, pri kasnejših popisih pa vrsta ni bila več potrjena (Foto: ivan Ergaver). 
continued inhabiting the pond in črni jarek (Figure 3) even though the meadows
around the pond were turned into pastures and fields in the years after the first record
of the species. Since this water body is relatively small, the negative effects of in-
creasing nutrient loads are to be expected in the future years. Additionally, grazing of
the cattle presents a disturbance to the riparian vegetation, which could lead to lower
water beetle diversity (gioria et al. 2010, Ambrožič et al. 2018).
Graphoderus bilineatus is more widespread and abundant in some countries neigh-
bouring Slovenia. in Hungary there are strong populations in the floodplains of the
rivers bodrog, tisza and Drava (Kalman et al. 2007, 2008, 2011, Soós et al. 2008)
and in croatia in the lowland part of the Drava and Sava rivers (temunović et al.
2011, turić et al. 2021). in italy, the species is rare and declining, since it is still
Øpela Ambroæiœ Ergaver, Andrej Kapla, Al Vrezec, Urøka Ratajc: Status of endangered Graphoderus bilineatus in Slovenia
193
Figure 3: the second recent location for Graphoderus bilineatus is in the old
riverbed of ledava river in murska šuma. the species was found here in the years
2017 and 2020 and probably represents the relict remnants of the population in
Slovenia (photo: Špela Ambrožič Ergaver).
Slika 3: Stara struga reke ledave v murski šumi je druga recentna lokacija za
ovratniškega plavača Graphoderus bilineatus. vrsta je bila tu najdena v letih 2017 in
2020 in verjetno predstavlja reliktni ostanek populacije v Sloveniji (Foto: Špela Am-
brožič Ergaver).
present only at one out of 15 historical sites, in the lake of pratignano (Fanano,
modena) within the parco dell'Alto Appennino modenese in Emilia-romagna (boscari
et al. 2020). to our knowledge, there are no known recent populations in southern
parts of Austria, which could suggest that the population along the mura river is
only a small isolated remnant of the former population and a possible relict popula-
tion.
According to our results, Graphoderus bilineatus is extremely rare in Slovenia
and thus extremely vulnerable. A change of species’ status in the national red list of
endangered species has already been suggested (Ambrožič et al. 2015a), however,
recent studies suggest that the species is at the brink of extinction in Slovenia. it is
necessary to establish strict protection of the areas where the species still occurs in
order to conserve the population in Slovenia. given the current knowledge, it is nec-
essary to designate the areas of the old ledava riverbed and gravel pit in Krapje as
natural reserves excluding management for fishing, agricultural or other human ac-
tivities and to dedicate it exclusively to strict nature protection. the area is located in
the Natura 2000 area of mura (Si3000215), but the current protection measures in
the area are not sufficient for effective long-term conservation of the species, which
is one of the most endangered beetle species in Slovenia and needs strict conservation
management with the highest level of conservation concern. A detailed action plan
for Graphoderus bilineatus is needed, which should include, among other adminis-
trative and technical requirements, the following categories:
(1) genetic analysis of relict population. to our knowledge, there are no other
historical or recent data (from Austria or croatia) (temunović et al. 2011) in mura
river region, which might suggest that the remnant population in Slovenia is a
possible relict population.
(2) Exploration of species reintroduction possibilities (source population, captive
breeding, release techniques) at the areas of previous (i.e. rače ponds) and recent oc-
currences (mura river). the current population is extremely small and probably facing
extinction due to an extremely fragmented habitat with low metapopulation capacity
(Hanski & ovaskainen 2002). As observed at the location in Krapje, local extinction
events are still ongoing and their prevention should therefore be a priority.
(3) revitalization of water bodies. to promote recolonization and to enable a
successful reintroduction we need to establish a suitable habitat for Graphoderus
bilineatus. thus, we propose the construction of water bodies with the following
properties:
a. the total surface area of the water body should be medium-sized (e.g. at least
8,000 m2; cuppen et al. 2006), because medium-sized water bodies were found
to support the richest water beetle communities (lundkvist et al. 2001).
b. the greater part of the basin of the water body should be at least 1 m deep (and
the central part of the water basin at least 1.5 m) (cuppen et al. 2006, Hendrich
& balke 2000).
c. Shading of the water body was found to negatively correlate with the abundance
of Graphoderus bilineatus (turić et al. 2021), therefore the water body should
not be completely shaded (cuppen et al. 2006). only part of the bank should be
Acta entomologica slovenica, 29 (2), 2021
194
overgrown with deciduous trees or shrubs (depending on the existing situation
at the site of the intervention), and most of the bank should be overgrown with
herbaceous vegetation (wetland vegetation with species such as Carex, Schoeno-
plectus, Sphagnum) (Hendrich & balke 2000).
d. the bottom of the water basin, with the exception of the central deepest part,
should be overgrown with submerged macrophytes (Utricularia, Ceratophyllum,
Hottonia, Potamogeton) (Hendrich & balke 2000). in general, dense vegetation
can represent a good shelter and oviposition sites for the beetles (gioria et al.
2010). Even though different diving beetle species have specific habitat re-
quirements, many studies found that rich aquatic macrophyte and riparian veg-
etation is positively influencing water beetle diversity and abundance (gioria et
al. 2011, Ambrožič et al. 2018). the presence of Graphoderus bilineatus posi-
tively correlates with species richness of water beetle communities (turić et al.
2021).
e. it must be ensured that the water is present permanently, at least in a part of the
established water body, because permanent water can support richer and more
diverse assemblages (gioria et al. 2010, Kolar & boukal 2020, turić et al.
2021).
f. Anthropogenic disturbances were found to have significant negative effects on
the abundance of Graphoderus bilineatus (turić et al. 2021). Access to the
water body should therefore be limited. it is also very important to prevent the
release of non-native fish species (eg. Lepomis gibbosus, Amerius melas, Pseu-
dorasbora parva), which negatively affect water beetle populations (Åbjörnsson
et al. 1997, Hendrich & balke 2000, Dudgeon et al. 2006). 
g. moderate nutrient loaded water bodies were found to support richest macrophyte
communities, and consequently higher water beetle diversity (Ambrožič et al.
2018). Following the water body establishment, it is therefore necessary to
monitor water beetle populations and basic physical and chemical parameters
in the area of both the newly established water body and the selected already
existing water bodies in the reserve.
(4) National management plan for the network of water bodies in accordance with
the requirements of the species.
Acknowledgments
the paper presents data collected within the targeted research of water beetles for
the preparation of reports and monitoring of species within the Natura 2000 network
in Slovenia, which were financed by the ministry of the Environment and Spatial
planning between 2008 and 2020 (representatives mag. juliana lebez-lozej, dr. peter
Skoberne). other data were obtained in the framework of various projects led and co-
financed by various organizations: Assessment of the situation for the Natura 2000
site in the voglajna river basin (leading partner: centre for cartography of Fauna and
Flora, financer: ministry of Agriculture and Environment), inventory of fauna and
flora on mura river area (leading partner: centre for cartography of Fauna and Flora,
Øpela Ambroæiœ Ergaver, Andrej Kapla, Al Vrezec, Urøka Ratajc: Status of endangered Graphoderus bilineatus in Slovenia
195
financer: Dravske elektrarne maribor d.o.o.) and life + livEDrivA: restoration of
the river ecosystem of the lowland part of the Drava in Slovenia (leading partner:
DoppS - birdlife Slovenia). we are grateful to our co-workers in the field: ivan Er-
gaver, martin vernik, matic gabor, dr. Dejan bordjan and dr. Alja pirnat. we thank
martin vernik for useful guidance in preparing the article.
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Vrezec A., Ambrožič Š., Kapla A. 2011: Dodatne raziskave kvalifikacijskih vrst
Natura 2000 ter izvajanje spremljanja stanja populacij izbranih ciljnih vrst
hroščev v letih 2010 in 2011. Carabus variolosus, Lucanus cervus, Rosalia
Acta entomologica slovenica, 29 (2), 2021
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alpina, Morimus funereus, Cucujus cinnaberinus, Cerambyx cerdo, Graphoderus
bilineatus. Končno poročilo. Nacionalni inštitut za biologijo, ljubljana: 128 pp.
Vrezec A., Ambrožič Š., Kapla A. 2012: Dodatne raziskave kvalifikacijskih vrst
Natura 2000 ter izvajanje spremljanja stanja populacij izbranih ciljnih vrst
hroščev v letu 2012: Carabus variolosus, Lucanus cervus, Rosalia alpina,
Morimus funereus, Graphoderus bilineatus. Končno poročilo. Nacionalni
inštitut za biologijo, ljubljana: 86 pp.
Vrezec A., Ambrožič Š., Kapla A. 2017: vpliv projektnih akcij na hrošče (projekt
life+ livEDrAvA). Končno poročilo. Nacionalni inštitut za biologijo, lju-
bljana: 84 pp.
Vrezec A., Ambrožič Š., Kapla A. 2017: monitoring populacij izbranih ciljnih vrst
hroščev v letih 2016 in 2017. Carabus variolosus, Lucanus cervus, Rosalia
alpina, Morimus funereus, Osmoderma eremita, Cucujus cinnaberinus,
Graphoderus bilineatus. Končno poročilo. Nacionalni inštitut za biologijo,
ljubljana: 72 pp.
Vrezec A., Ambrožič Ergaver Š., Kapla A., Kocijančič S., Čandek K., Ratajc U.,
Žunič Kosi A. 2020: Dodatne raziskave kvalifikacijskih vrst Natura 2000 ter iz-
vajanje spremljanja stanja populacij izbranih ciljnih vrst hroščev v letih 2018,
2019 in 2020: Carabus variolusus, Lucanus cervus, Rosalia alpina, Morimus
funereus, Osmoderma eremita, Cucujus cinnaberinus, Leptodirus hochenwartii,
Graphoderus bilineatus. Končno poročilo. Nacionalni inštitut za biologijo, lju-
bljana: 156 pp.
Received / Prejeto: 21. 10. 2021
Øpela Ambroæiœ Ergaver, Andrej Kapla, Al Vrezec, Urøka Ratajc: Status of endangered Graphoderus bilineatus in Slovenia
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