Re d is c o v e Ry a n d d is t Ribu t io n o f t h o R's f Rit il l a Ry
BOLORIA THORE (h ü bn e R, 1803) (l e pid o pt e Ra : n y mph a l id a e ) 
in s l o v e n ia
Rudi Ve Ro Vn ik
1
, Primož Gl o Go Vč a n
2
, Stanislav Go mb o c
3
1
Univerza v l jubljani, b iotehniška Fakulteta, o ddelek za biologijo, Jamnikarjeva
101, 1000 l jubljana; e-mail: rudi.verovnik@bf.uni-lj.si
2
č irče 63, 4000 k ranj; e-mail: primoz.glogo@gmail.com
3
Gančani 110, 9231 b eltinci, e-mail: stanislav.gomboc@siol.net
a bstract  Thor's Fritillary (Boloria thore) has been considered extremely rare and
localised at the south-eastern edge of its distribution in the a lps, especially in Slovenia.
Despite surveys focused on sites with historical records (Julian a lps, k aravanke
mts.), there is almost a century long gap with no observations. its discovery on the
south-eastern slopes of mt. k ošuta (k aravanke mts.) in 2004 was therefore unexpected,
however within the known historical range of the species in the region. Since its re-
discovery, the species has been observed at several new localities in the k aravanke
mts. and Julian a lps. These records are presented and habitat requirements as well as
potential threats for the species are discussed.
k e y w o RDS: Papilionoidea, montane species, habitat, endangerment
izvleček  Po n o Vn o o Dk RiTJe Te mn e Ga TRa Ta RJa BOLORIA THORE
(Hü b n e R, 1803) (l e PiDo PTe Ra : n y mPHa l iDa e ) in n Je Go Va Ra z š iR-
Je n o ST V Sl o Ve n iJi
Temni tratar (Boloria thore) velja na jugovzhodnem robu svoje razširjenosti v a l-
pah, zlasti v Sloveniji, za izredno redko in lokalno razširjeno vrsto. k ljub načrtnemu
pregledu znanih zgodovinskih lokacij (Julijske a lpe, k aravanke) ga pri nas skoraj
100 let nismo našli. n jegovo ponovno odkritje na jugovzhodnih pobočjih k ošute
(k aravanke) leta 2004 je bilo nepričakovano, pa čeprav znotraj znanega zgodovinskega
območja razširjenosti vrste v regiji. o d ponovnega odkritja je bila vrsta potrjena na
več novih lokacijah v k aravankah in Julijskih a lpah. Te najdbe predstavljamo v pri-
spevku, kjer razpravljamo še o habitatu in potencialni ogroženosti te vrste.
k l JUč n e b e Se De : Papilionoidea, montanske vrste, življenjski prostor, ogroženost
149
ACTA ENTOMOLOGICA SLOVENICA
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introduction
Thor’s fritillary is a boreo-alpine species distributed in the northern Palaearctic
region from Japan in the east (Tuzov & b ozano 2006), throughout northern a sia to
boreal northern e urope with a disjunct range in the a lps (Tolman & l ewington
2008). Here it is distributed mainly in the c entral and e astern a lps, reaching the
northern Piedmont region at the south-western edge of the distribution (mérit &
manil 2016). it is more widespread in the northern part of the a lps (e.g. b avaria -
n unner 2013), becoming much scarcer towards south (e.g. South Tyrol – Huemer
2004, Dolomites - b onato et al. 2014).
it is a predominantly woodland species favouring coniferous forest clearing or
open coniferous or mixed woods in the montane belt in the a lps (Pro n atura 1987,
w eidemann 1995). it is often found on shaded clearings, along dump forest edges,
ravines and mountain streams with abundance of nectar sources (Pro n atura 1987,
Tolman & l ewington 2008, n unner 2013). a dults have a slower and more gliding
flight compared to other species in the genus and are often visiting flowers, or
perching on low bushes and young firs (Gorbunov & k osterin 2007). Flight period in
the a lps is from mid-June to beginning of a ugust depending on altitude and season
(Tolman & l ewington 2008). Due to large fluctuations in numbers of adults a biannual
lifecycle has been anticipated (Pro n atura 1987), however not confirmed (Huemer
2004). The larvae feed on different Viola spp., in the a lps most commonly on Viola
biflora l . (Pro n atura 1987). The species in general is not considered threatened in
e urope (van Swaay et al. 2010), however local populations at the edge of the distri-
bution can be affected by afforestation of clearings, intensive forest management,
overgrowing of open forest areas or development of infrastructure (ski pists, etc.)
(n unner 2013).
o nly three historical records were published for Thor's Fritillary in Slovenia. it
was first reported by Hafner (1909) in his comprehensive overview of the fauna of
the k rain region based on specimens collected by Hans k autz in the northern Julian
a lps in Pišnica Valley (18.6.1908) and at e rjavčeva hut near Vršič Pass (9.7.1908)
(also mentioned in Rebel 1910). a dditionally, it was reported from mt. b aba in k ar-
avanke mts. (18.7.1906) (Galvagni 1910), however without precise information on
the locality. it is likely, that the species was found on the southern side of the mountain
(in Slovenia) as Galvagni mentions mojstrana town as a starting point of his explo-
rations (Galvagni 1910). There is also an additional record for mt. Stol in the same
range based on a specimen in Vienna n atural History museum (Verovnik et al. 2005),
however it is likely that the specimen was collected on the northern (a ustrian) side of
the mountain where the species is known to occur in nearby b ärental (Thurner 1948).
Thurner (1948) also mentions the species from Quadia a lm in close proximity of the
Slovenian border near mt. Golica, and several other mountain ranges in c arinthia
(k oralpe, Saualpe, Dobratsch, c arnic a lps). in k oralpe, just north of the Slovenian
border near Drava River, the species was reported from both the c arinthian and
Styrian part of the range (Höfner 1885, 1903, 1911, k ühnert 1966, 1978). n o published
Acta entomologica slovenica, 28 (2), 2020
150

records from Friuli region could be retrieved, but species was known to occur near
Fužine l akes close to Slovenian border (š tanta Radovan, pers. observ.).
Thor’s Fritillary was rediscovered in Slovenia in 2004 at Dolge n jive pastures be-
low mt. k ošutnik in the eastern part of k aravanke mts. (Gomboc, pers. observ.) and
at several nearby sites in the subsequent years (Verovnik et al. 2012). a more detailed
account of these records and additional records from western k aravanke mts. and Ju-
lian a lps are discussed in our overview.
methods
Focused species surveys for Thor’s fritillary were based on historical records and
presence of the potentially suitable habitat, mainly along streams and forest roads
since the year 2000. maps with orthophoto images, such as Geopedia (http://www.geo-
pedia.si/) and a tlas okolja (http://gis.arso.gov.si/atlasokolja/) were also used for de-
tection of the potential habitats. b utterflies were netted and released after examination,
Rudi Verovnik, Primoæ Glogovœan, Stanislav Gomboc: Rediscovery and distribution of thor's fritillary Boloria thore
151
f ig. 1: The distribution of the Thor’s fritillary (Boloria thore) in south eastern
a lps. n ew records (green dots) are added to the known locations (red squares) based
on literature data and database queries (see methods).
s l. 1: Razširjenost temnega tratarja (Boloria thore) v jugovzhodnih a lpah. n ovi
podatki (zelene točke) so dodani k znanim lokacijam (rdeči kvadratki) iz literature in
baz podatkov (glej metode).

or were observed without disturbance. a dults and habitats were documented by pho-
tographing. 
Distribution map (Fig. 1) was prepared in e SRi a rcGiS Pro software, based on
observation presented in this contribution, the literature data, and records from
databases z o b o Da T (https://www.zobodat.at/), Gb iF (https://www.gbif.org/), and
o bservation (https://observation.org/).
Results
Since the year 2000, which marks the large scale faunistic surveys for the butterfly
atlas of Slovenia (Verovnik et a. 2012), but also earlier, the first author visited all
three historical sites (Velika and mala Pišnica Valleys, Vršič pass, mt. b aba) with
the former presence of Thor’s fritillary on several occasions, however without any
success. a part from the open forest and small streams on the northern side of the
Vršič pass, no potentially suitable habitat was found. The known site at nearby l ago
di Fusine in italy was also visited with a single observation in 1999 (see Table 1). in
the last decade the open forests near the lake were greatly reduced and large intensive
pastures have been established, so no additional observations were made.
Acta entomologica slovenica, 28 (2), 2020
152
f ig. 2: Thor’s fritillary (Boloria thore) underside. Photographed at the quarry
below mt. k ošutnik. (photo: Rudi Verovnik)
s l. 2: Temni tratar (Boloria thore), spodnja stran. Fotografiran pri kamnolomu
pod k ošutnikom. (foto: Rudi Verovnik)

Rudi Verovnik, Primoæ Glogovœan, Stanislav Gomboc: Rediscovery and distribution of thor's fritillary Boloria thore
153
t able 1: l ist of localities and dates of the recent observations of Thor’s fritillary
(Boloria thore) in south-eastern a lps.
t abela 1: Seznam lokalitet in datumov novejših najdb temnega tratarja (Boloria
thore) v jugovzhodnih a lpah.
date locality l at (w GS84) l on (w GS84) a ltitude (m)
31.7.2004 Si, Tržič, mt. k ošuta, upper part of the
Dolge njive pastures along the dry
stream in the woods
46°26′18″ 14°25′10″ 1465
12.7.2006 Si, Tržič, mt. Veliki Javornik, along the
road 500 m Gaberčev rovt pastures
46º 22′ 38″ 14º 23′ 16″ 1440
12.7.2006 Si, Tržič, mt. Veliki Javornik, glades
and pastures at the saddle n of the
mountain
46º 22′ 47″ 14º 24′ 17″ 1470
12.7.2006,
4.7.2014,
19.6.2018,
7.7.2018
Si, Tržič, mt. Veliki Javornik, along a
small stream in the valley e of
k onjščica peak
46º 23′ 04″ 14º 23′ 29″ 1380
6.7.2006 Si, Tržič, mt. k ošuta, clearings along
the road south east of the č rna Peč peak
46º 25′ 21″ 14º 25′ 12″ 1210
19.6.2018 Si, Tržič, mt. k ošuta, along the stream
and road in the valley n of k ošutnik
hut
46º 25′ 51″ 14º 24′ 01″ 1140
6.7.2006,
2.7.2007,
15.6.2011,
11.7.2015,
19.6.2018
Si, Tržič, mt. k ošuta, along the road
near the small abandoned quarry
46º 26′ 05″ 14º 24′ 38″ 1290
6.7.2006 Si, Tržič, mt. k ošuta, lower part of the
Dolge njive pastures and along the dry
stream
46º 26′ 15″ 14º 24′ 56″ 1380
24.7.2018,
25.6.2019,
9.7.2020
Si, k ranjska Gora, mt. Trupejevo
Poldne, first part of the Železnica valley 46º 30′ 43″ 13º 50′ 37″ 1500
27.6.1999 iT, Fusine in Valromana, l ago di
Fusine, small glade south-west of the
upper lake
46° 28′ 29″ 13° 39′ 54″ 930
29.6.2019 iT, mt. Jerebica, clearing along the
track w of Jezerski pass
46° 23′ 39″ 13° 32′ 45″ 1610

The rediscovery of Thor's Fritillary in 2004 was completely coincidental, during an
inventory of grasshoppers and butterflies. o nly a single worn individual was observed
in open spruce forest near dry stream at Dolge njive pastures. a more detailed survey
of the wider region between mt. k ošuta and mt. Storžič followed in 2006 when the
species was recorded at six additional sites. main common characteristics of the localities
are the presence of open coniferous woods with open areas along roads and in most
cases also small streams. a bundance of flowering plants was noted along the streams
and on road verges providing the necessary nectar sources for the adults. w e noticed
different Cirsium sp., Knautia sp., and Thymus sp. as the main nectar source of the
adults. The males commonly perched on small spruces or bushes 2 to 3 meters above
the ground, sometimes returning to the same perch when disturbed. They were also ob-
served patrolling along streams or roads, while females were busier visiting the flowers.
mostly, they were present in low numbers from 1 to 5 specimens per site, however in
2006 they were common near the small abandoned quarry below mt. k ošuta (Fig. 2).
c losely related, montane woodland habitat specialist, Titania's fritillary (Boloria titania
(e sper, 1793)) has been found cohabiting at most of these sites.
in 2018 the species has finally been discovered also in the western k aravanke
mts., much closer to the historical mt. b aba locality, in Železnica Valley. The first
Acta entomologica slovenica, 28 (2), 2020
154
f ig.3: Habitat of Thor’s fritillary (Boloria thore) in the lower part of the Železnica
Valley, western k aravanke mts. (photo: Primož Glogovčan)
s l. 3: Življenjski prostor temnega tratarja ((Boloria thore) v spodnjem delu doline
Železnica, zahodne k aravanke. (foto: Primož Glogovčan)

author visited the valley on two previous occasions, but possibly too late in the
season, as only Titania's fritillary was recorded. The habitat is otherwise ideal for
both fritillaries with open fir and larch woods on both slopes and glades along the
stream and the narrow road meandering through the valley (Fig 3). The presence of
the species was confirmed also in both consecutive years, with largest abundance of
about a dozen of specimens seen in 2020.
The discovery of the species at the mt. Jerebica (Jezerski pass) in the western
Julian a lps just across the border in italy was a bigger surprise, as the habitat there is
steep grassy slope with dwarf pine and small fir trees near the ridge surrounded by
otherwise dense montane forest with no stream in vicinity. Such habitat combination
is widespread throughout Julian a lps in particularly on the eastern and northern edge
of the range. a pproximately ten adults were observed, some feeding on thistles
Adenostyles alliariae (Gouan) a .k ern. (Fig. 4).
d iscussion
Given the recent records, the Thor’s fritillary is obviously not that extremely rare
in south-eastern a lps as adjudging from the long gap between historical and recent
Rudi Verovnik, Primoæ Glogovœan, Stanislav Gomboc: Rediscovery and distribution of thor's fritillary Boloria thore
155
f ig.4: Thor’s fritillary (Boloria thore) feeding on Adenostyles alliariae near
Jezerski pass, mt. Jerebica in western Julian a lps. (photo: Primož Glogovčan)
s l. 4: Temni tratar ((Boloria thore) se hrani na Adenostyles alliariae v bližini Jez-
erskega prelaza pri Jerebici v zahodnih Julijskih a lpah. (foto: Primož Glogovčan)

observations (Verovnik et al. 2012). This could be explained by its low detectability
due to short flight period, low adult abundance (possibly due to biannual life cycle
(Pro n atura 1987)), and extremely localised distribution linked to availability of suit-
able open coniferous forest habitat. o ur records span form mid-June to end of July,
which is in line with observations elsewhere in the a lps (Pro n atura 1987, Tolman &
l ewington 2008), however locally the adults are on the wing not more than three
weeks with a peak of occurrence in Slovenia at the beginning of July.
The species is possibly more widespread in the south-eastern a lps and we expect its
wider distribution in the k aravanke mts., northern Julian a lps, and anticipate its possible
occurrence also in the Pohorje mts. further eastwards. n amely, the Thor’s fritillary has
been recorded from nearby k oralpe (Höfner 1885, 1903, 1911, k ühnert 1966, 1978)
and both ranges share at least one boreo-alpine butterfly species Argiades optilete
(k noch, 1781) (k ühnert 1978, Jež 1983). Potentially suitable habitats for Thor’s fritillary
are present on the northern side of the Pohorje mts. but so far no focused search has
been undertaken. The geographically even closer to k oralpe are k ozjak mts. at the
border with a ustria, but they are probably too low and with a predominantly southern
exposition, therefore not likely to have any suitable habitat for the species.
The Thor’s fritillary is listed as vulnerable in the a lpine region in the first published
Red list of butterflies of Slovenia (c arnelutti 1992) with a note, that it has not been
observed for a ‘while’. in the a tlas of threatened butterflies of Slovenia (č elik & Re-
beušek 1996) it is considered extinct and was therefore not evaluated for the official
red list of the l epidoptera of Slovenia (o fficial Gazette 2004). The status of a vul-
nerable species has been proposed also in the Slovenian butterfly atlas (Verovnik et
al. 2012) due to extreme localised distribution. Taking into consideration our recent
findings we are inclined to lower its extinction risk to near threatened, as we show
that the Thor’s fritillary has a wider distribution in Slovenia and is predominantly
distributed in areas with low human impact. Still majority of the populations are
highly localised and possibly isolated, thus vulnerable to local habitat change (e.g.
road construction, logging, afforestation) and over-collecting. a lthough climate
change could also be considered a long term threat for such montane butterflies
(Settele et al. 2008), a much more detailed survey and a longer time span would be
required to substantiate this.
The current forest management, particularly in the k aravanke mts., is suitable for
long term maintenance of the habitat for the Thor’s fritillary with large areas of open
spruce woods, clearings, and fellings. Pasturing, to a smaller extent, is also important
for maintenance of open habitat structures bellow the treeline, which are perquisite
for flower rich areas required by the species. w e hope our publication will trigger
further surveys and research of this interesting species at its southern edge of the dis-
tribution in e urope.
a cknowledgment
The field work of Rudi Verovnik was partially funded by the Slovenian Research
agency (program P1-0184).
Acta entomologica slovenica, 28 (2), 2020
156

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