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eISSN: 2284-4880 (online version)
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Introduction
From the perspective of biological conservation, spiders
(Araneae, Arachnida) are among the less explored taxa, al-
though they are one of most important groups in terms of
adaptive radiation and its ecological role as top-predators.
Among the 1,632 known species in Italy (Pantini & Isaia
2017) - one of the most species-rich countries in Europe
- only few species are considered by international and na-
tional conservation policies (Milano et al. 2018).
Among them, the great raft spider, Dolomedes plantar-
ius (Clerck, 1757) (Araneae, Pisauridae) is a large-sized
spider (male body-length: 10-16 mm; female body-length:
13-20 mm; Nentwig et al. 2018) closely associated with
lowland wet habitats. Together with the congeneric D.
mbriatus (Clerck, 1757), it is the only representative of
the genus in Europe. Despite the two species share similar
ecological requirements and may be found in syntopy, D.
plantarius is considered rarer and more stenoecious than
D. mbriatus, the former being strictly associated with
standing waters such as rushlands, sedgelands and fens,
and the latter associated with a variety of swampy areas,
including owing waters, alluvial forests and bog forests.
Due to the high variability of the body coloration and
size, the correct identication of the two European spe-
cies is possible only by means of the examination of sex-
ual characters under the stereomicroscope (van Helsdin-
gen 1993).
As the vernacular name suggests, the great raft spider
is closely associated with standing meso-oligotrophic wa-
ters, from which many aspects of its life-history depend,
from feeding to courtship and reproduction (Duffey 1995;
van Helsdingen 1993). Individuals can be found along the
edges of marshlands, bogs, canals, turf ponds and swamps,
hunting on the water surface or among emergent and mar-
ginal vegetation, where females build their typical nurs-
ery webs.
Although Bonnet (1930) considered D. plantarius
widespread all over the Palearctic region, the species is lo-
cally rare, suggesting a high vulnerability and a declining
trend over much of the range (Duffey 1995; van Helsdin-
gen 1993). In particular, the decline is related to the loss
and the degradation of wetland habitats, namely of low-
land fens, to the fragmentation of the populations, that are
genetically isolated, and to the progressive eutrophication
of the water throughout much of its range (Smith 2000).
As the result of its extreme vulnerability, the species is
listed in the Regional Red Lists of several European coun-
tries (see Milano et al. 2018). In the United Kingdom, the
species is classied as Vulnerable (Harvey et al. 2017), is
Fragmenta entomologica, 50 (1): 69-74 (2018)
Research article
Submitted: May 18th, 2018 - Accepted: June 10th, 2018 - Published: June 29th, 2018
Notes on the Italian distribution of Dolomedes plantarius (Clerck, 1757),
species assessed for the IUCN Red List
(Araneae: Pisauridae)
Filippo MILANO 1, Paolo PANTINI 2, Riccardo CAVALCANTE 3, Marco ISAIA 1,*
1 Laboratory of Terrestrial Ecosystems, Department of Life Sciences and Systems Biology, University of Torino - Via Accademia
Albertina 13, 10123 Torino (TO), Italy - lippo.milano@unito.it; marco.isaia@unito.it
2 Museo Civico di Scienze Naturali “E. Caf”, Bergamo - Piazza Cittadella 10, 24129, Bergamo (BG), Italy
ppantini@comune.bergamo.it
3 Cultural Association Docet Natura, Section Biodiversity, Centro Emys Piemonte - Via del Molino 12, 13046 Livorno Ferraris (VC),
Italy - scaval@hotmail.it
* Corresponding author
Abstract
The great raft spider, Dolomedes plantarius, is a semi-aquatic spider species with an Eurosiberian distribution. As a result of habitat loss
and degradation, in 1996 the species was classied as Vulnerable in the IUCN Red List of Threatened Species, but since then the status
has never been updated. We present the frame of the existing knowledge on the distribution of this rare spider species in Italy, based on
literature data and on original records gathered in recent years. Finally, we discuss the conservation value of the Italian populations, in
light of their peripheral position within the species range and in light of the future reduction of the bioclimatic range of the species due
to climate and land cover changes associated with anthropic disturbance.
Key words: Great raft spider, wetlands, habitat loss, conservation.
70
Milano et al.
fully protected under Schedule 5 of the Wildlife and Coun-
tryside Act 1981 and is the subject of a Species Action
Plan (UK Biodiversity Steering Group 1999). In the light
of this, a translocation program was initiated in 2010, with
the establishment of three new populations at new sites in
the Norfolk and Suffolk Broads (Harvey et al. 2017; Smith
& Baillie 2011).
The species entered the IUCN Red List of Threatened
Species in 1996, being included in the Vulnerable catego-
ry (World Conservation Monitoring Centre 1996). Since
then, the assessment has never been updated. New infor-
mation on the species distribution available at the Euro-
pean level and recent studies demonstrating the dramatic
consequences of climate and land cover changes on the
range of the species, rmly underline the need of a revision
of its conservation status.
In this paper, we present the frame of the existing
knowledge on Dolomedes plantarius in Italy, based on
literature data and on original records gathered in recent
years. In light of our results and considering the role of
Italian populations in the conservation of the species, we
underline the need for long term monitoring programs,
aiming to assess the status of the Italian populations and
the need of further studies, aiming at deepening the knowl-
edge about the distribution and the ecology of the Italian
populations.
Material and Methods
We examined all available literature data referring to the
presence of Dolomedes spiders in Italy. For the biblio-
graphic survey, we referred to the reference list of the up-
dated version of the Italian checklist of the Italian spiders
(Pantini & Isaia 2017).
Moreover, we checked for the presence of Dolomedes
spiders in private and Museum collections in Italy, and
we conducted a number of eld activities in northern Ita-
ly (2014-2018) with the help of different contributors (see
acknowledgments), with a special focus on the region of
Piemonte. The individuals collected were examined and
identied using a Leica M80 stereoscopic microscope (up
to 60x magnication). Specimens are preserved in 75° eth-
anol and are stored in Marco Isaia’s collection at the De-
partment of Life Sciences and Systems Biology of the Uni-
versity of Torino.
Results
The distribution of Dolomedes plantarius in Italy is pre-
sented in Fig. 1 and detailed in Tab. 1. The bibliograph-
ic survey led us to record the occurrence of this species
in Piemonte, Lombardia, Veneto, Emilia-Romagna, Tos-
cana and Sardegna. A number of outdated references doc-
umenting the occurrence of this species in Lombardia
(Pavesi 1873, 1879), Veneto (Contarini 1843) and Campa-
nia (Trani 1902) were considered doubtful due to the high
degree of uncertainty of the identications [the same crite-
ria was adopted by Brignoli (1977) in a rst outline of the
Italian distribution of this species].
Our eld activities led to the discovery of several new
records in the rice-growing area of Piemonte (16 locali-
ties) and in the wetland of Punta Alberete (Emilia-Romag-
na). Most of the records fall within natural protected areas.
Material
Piemonte: Province of Torino: Candia, shores of Lago
di Candia (Reed bed), Parco Naturale del Lago di Can-
dia, 21.VII.2010, Paschetta leg. 1 ♂. Province of Ales-
sandria: Valenza, Lanca di San Bernardo (oxbow lake),
“Parco uviale del Po tratto vercellese/alessandrino e Ris-
erva Naturale del torrente Orba”, 10.VIII.2011, Paschetta
leg. 1 ♀; Camino, Lanca di Brusaschetto (oxbow lake),
“Parco uviale del Po tratto vercellese/alessandrino e Ris-
erva Naturale del torrente Orba”, 07.V.2018, Cavalcante
leg. 1 ♀; Frassineto Po, Lanca Terranova, “Parco uvi-
ale del Po tratto vercellese/alessandrino e Riserva Natu-
rale del torrente Orba”, 24.V.2018, Cavalcante, Isaia &
Milano leg. 1 ♀; Lanca Sesia Morto, “Parco uviale del
Po tratto vercellese/alessandrino e Riserva Naturale del
torrente Orba”, 24.V.2018, Cavalcante leg. 1 ♂. Province
of Vercelli: Livorno Ferraris, Fontana Leira, 10.VII.2014,
Cavalcante & Evangelista leg. 1 ♂; Castell’apertole, Cen-
tro Emys Piemonte, 27.V.2018, Cavalcante & Fiore leg.
1 ♂; Tricerro, Fontana Gigante, “Riserva Naturale Spe-
ciale di Fontana Gigante”, 27.VIII.2015, Cavalcante leg.
1 ♀; VII.2015, Cavalcante leg. 1 ♀; Crescentino, “Palude
di San Genuario, Riserva Naturale Speciale e Zona di Sal-
vaguardia della Palude di San Genuario”, 10.VI.2015,
Cavalcante leg. 1 ♂; 23.V.2018, Cavalcante leg. 1 ♂; Al-
bano Vercellese, “Parco uviale delle lame del Sesia” (ox-
bow lake), 25.V.2017, Cavalcante & Fiore leg. 1 ♂; Trino,
Madonna delle Vigne (fen), 06.VI.2017, Cavalcante leg.
1 ♂; Ronsecco, Lachelle, Prato Lungo (fen), 21.VII.2017,
Fasano leg. 1 ♀; Palazzolo Vercellese, in an irrigation ca-
nal, 14.IV.2018, Cavalcante & Fiore leg. 1 ♂; wetland in
the nearby of the village, “Parco uviale del Po tratto ver-
cellese/alessandrino e Riserva Naturale del torrente Orba”,
05.V.2018, Cavalcante leg. 1 ♂. Emilia-Romagna: Prov-
ince of Ravenna, Punta Alberete, “Parco del Delta del Po”,
VII.2015, Cavalcante leg. 1 ♀.
Discussion
Dolomedes plantarius is closely associated with lowland
wetlands, a delicate habitat increasingly subjected to al-
teration mostly due to changes in the water regime, phys-
ical modication, eutrophication and pollution. Just like
other wetland species, as a result of habitat degradation
and loss (Davidson 2014), populations of D. plantarius are
71
On the Italian distribution of Dolomedes plantarius
facing a remarkable decline. This has prompted a number
of conservation authorities and several European countries
to consider D. plantarius threatened with extinction (see
Milano et al. 2018).
In relation to the progressive loss of its natural habitat,
in 1983, D. plantarius was rstly reported in the IUCN In-
vertebrate Red Data Book as a species in need of conser-
vation (Wells et al. 1983). Some years later, based on sim-
ilar arguments, Collins & Wells (1987) reported D. plan-
tarius among the threatened invertebrates in Europe, and
proposed the species as a suitable candidate for inclusion
in the Appendix II of the Bern Convention. The rst of-
cial assessment of the conservation status of the species
dates back to 1986, with the inclusion of D. plantarius in
the Vulnerable category (IUCN Conservation Monitoring
Center 1986). This status was maintained in the following
updates of the Red List (Groombridge 1993; IUCN 1990;
Wilcox 1988). After the publication of the 1994 IUCN
Red List Categories and Criteria (version 2.3), D. plan-
tarius was re-assessed and again placed in the Vulnerable
category against criterion A (i.e. population size reduction;
World Conservation Monitoring Centre 1996). However,
being assessed before the publication of the new IUCN
standards (version 3.1, 2001), the evaluation of D. plan-
tarius remains outdated and hardly comparable with the
recent ones.
Regardless of the outdated IUCN assessment, many
European countries recognized the importance of the con-
servation of this spider and listed it on their Regional Red
Lists. Currently, D. plantarius is cited in the Red List of
the following European countries: Finland (Rassi et al.
2010), Norway (Henriksen & Hilmo 2015), Great Brit-
ain (Harvey et al. 2017), Flanders (Belgium, Maelfait et
al. 1998), Germany (Blick et al. 2016), Austria (Carinthia;
Komposch & Steinberger 1999), Czech Republic (Řezáč
et al. 2015), Slovenia (Gajdoš & Svatoň 2001), and the
region of the Carpathian Mountains (Gajdoš et al. 2014).
Concerning Italy, D. plantarius is mentioned as Vul-
nerable on the List of the Threatened Invertebrates of the
Italian Fauna (Groppali & Priano 1992) and in the region-
al legislation of Lombardia, where it is listed in the D.g.r.
8/773 24.07.2008 among invertebrates of regional interest
(see Milano et al. 2018).
In Italy, D. plantarius seems mostly distributed in the
Northern district (Fig. 1), namely in Piemonte (Leroy et
al. 2013; this work), Lombardia (Vugdelić, 2006 in Leroy
et al. 2013), Veneto (Hansen 2002, 2007) and Emilia-Ro-
magna (this work). However, the species has been for-
merly reported in central and southern Italy (see Tab. 1
and Fig. 1). Data from Toscana (di Caporiacco 1936) and
Sardegna (Kraus 1955) refer to plausible records dating
back to the rst half of XX century. These isolated locali-
ties represent the southernmost records for the species in
Italy and gure among the southernmost in Europe.
In accordance with Brignoli (1977) and van Helsdin-
gen (1993), old citations dating back to XIX century are
in need of verication, due to the confusion of D. plan-
tarius with D. mbriatus. Accordingly, before Bonnet
(1930), D. plantarius was called D. mbriatus, while D.
mbriatus was referred to as D. limbatus (Hahn, 1831),
making many published records not reliable (van Helsdin-
gen 1993). More specically, the presence of D. planta rius
in the province of Naples (Campania) reported by Trani
(1902), is uncertain, being more likely based on specimens
of D. mbriatus. Similarly, records from the provinces of
Pavia (Pavesi 1873) and Varese (Pavesi 1879) in Lombar-
dia also need verication. However, the presence of the
species in this region is validated by the records of Bonnet
(1930) for Brianza and Vugdelić (2006) for the province of
Varese. Similarly, data on the occurrence of D. plantarius
in Veneto by Contarini (1843), were conrmed by the re-
cent records of Hansen (2002, 2007).
The Italian situation is particularly critical, due to the
geographical isolation of the populations at the periphery
of the range. Peripheral populations are often genetically
and morphologically divergent from central populations,
and are particularly important for the evolutionary future
of the species (Lesica & Allendorf 1995). In the case of
D. plantarius, this frame is particularly dramatic in view
of the predicted north shift of the species caused by cli-
matic changes (Leroy et al. 2013). Accordingly, species
distribution models predict a sharp decrease of the current
suitable range, with a remarkable loss in the South and the
appearance of newly-suitable areas in the North. In con-
sequence of that, the condition of the Italian populations
appears particularly critical: the Alpine barriers blocking
the species dispersion northward, will preclude the species
from reaching future more suitable areas located North of
the Alps. Therefore, the only available option for these pe-
ripheral populations will be the unlikely local adaptation
to the new environmental conditions.
Moreover, it seems likely that in the Italian northern
districts, the progressive loss of wetlands resulting from
agricultural exploitation have fragmented and jeopardized
natural populations, which are now restricted to natural
protected areas. This seems particularly remarkable in the
provinces of Vercelli and Alessandria (Piemonte), where
natural lowland wetlands are widely replaced by rice
elds. Intensive agricultural use in these renowned rice-
growing areas, associated with changes in the hydrological
regime and water pollution due to agricultural products,
resulted in a severe alteration of the natural ecosystems,
with dramatic consequences on the survival of populations
of D. plantarius. Accordingly, it seems likely that most of
the populations currently survive in unexploited protected
wetlands, i.e. "Parco uviale del Po tratto vercellese/ales-
sandrino e Riserva Naturale del torrente Orba", S.I.C. Fon-
tana Gigante and S.I.C. Palude di San Genuario. Despite
additional studies which may further support this hypoth-
esis, we argue that the preservation of the wetland habi-
tat is crucial for the conservation of the species. It seems
clear that, in lack of specic conservation measures and
72
Milano et al.
Table 1 – List of the Italian records of Dolomedes plantarius (Clerck, 1757).
Emilia-
Romagna
Lombardia
Lombardia
Lombardia
Lombardia
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Piemonte
Sardegna
Toscana
Toscana
Veneto
Veneto
Veneto
Ravenna (RA)
Pavia (PV)
Varese (VA)
–
Corgeno (VA)
Verbania (VB)
Verbania (VB)
Candia (TO)
Candia (TO)
Candia (TO)
Candia (TO)
Candia (TO)
Valenza (AL)
Livorno Ferraris (VC)
Tricerro (VC)
Crescentino (VC)
Palazzolo Vercellese (VC)
Trino (VC)
Albano Vercellese (VC)
Crescentino (VC)
Camino (AL)
Frassineto Po (AL)
Palazzolo Vercellese (VC)
Frassineto Po (AL)
Livorno Ferraris (VC)
Tricerro (VC)
Ronsecco (VC)
Sassari (SS)
Monterchi (AR)
Arezzo (AR)
Padova (PD) and Venezia
(VE)
Quarto d'Altino (VE)
Venezia (VE)
Punta Alberete
Unspecied locality
Isolino di Varese
Unspecied locality in Brianza (MB)
Lago di Comabbio
Lake margin near Camping Isolino
(Reed bed)
Lake margin near Camping Isolino
(Reed bed)
Shores of Lago di Candia (Reed bed)
Shores of Lago di Candia (Reed bed)
Shores of Lago di Candia (Reed bed)
Shores of Lago di Candia (Reed bed)
Shores of Lago di Candia (Reed bed)
Lanca di San Bernardo (oxbow lake)
Fontana Leira
Fontana Gigante
Palude San Genuario
Nearby of Palazzolo Vercellese
(irrigation canal)
Madonna delle Vigne (fen)
Parco uviale delle lame del Sesia
(oxbow lake)
Palude San Genuario
Lanca di Brusaschetto (oxbow lake)
Lanca Terranova
Wetland in the nearby of the village
Lanca Sesia Morto
Castell'apertole. Centro Emys Piemonte
Fontana Gigante
Lachelle, Prato Lungo
Unspecied locality
Unspecied locality
Alluvial deposits of Tevere
Padova and Venezia
(unspecied locality)
San Michele Vecchio
(oxbow lake of Sile)
Laguna di Venezia, Valle Averto
This work
Pavesi, 1873
Pavesi 1879
Bonnet 1930
Vugdelić 2006 in
Leroy et al. 2013
Leroy et al. 2013
Leroy et al. 2013
Leroy et al. 2013
Leroy et al. 2013
Leroy et al. 2013
Leroy et al. 2013
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
Kraus 1955
Di Caporiacco 1936
Di Caporiacco 1936
Contarini 1843
Hansen 2002
Hansen 2007
2018
1873
1878
1930
2002
2009
2009
2010
2010
2010
2010
2010
2011
2014
2015
2015
2018
2017
2017
2018
2018
2018
2018
2018
2018
2015
2017
1952
1925
1926
1843
1992
1992
Parco del Delta del Po
–
Riserva Naturale Palude Brabbia
–
–
Riserva Naturale Speciale del Fondo Toce
Riserva Naturale Speciale del Fondo Toce
Parco Naturale del Lago di Candia
Parco Naturale del Lago di Candia
Parco Naturale del Lago di Candia
Parco Naturale del Lago di Candia
Parco Naturale del Lago di Candia
Parco uviale del Po tratto vercellese/
alessandrino e Riserva Naturale del torrente Orba
–
Riserva Naturale Speciale di Fontana Gigante
Riserva Naturale Speciale e Zona di
Salvaguardia della Palude di San Genuario
–
–
Parco uviale delle lame del Sesia
Riserva Naturale Speciale e Zona di Salvaguardia
della Palude di San Genuario
Parco uviale del Po tratto vercellese/
alessandrino e Riserva Naturale del torrente Orba
Parco uviale del Po tratto vercellese/
alessandrino e Riserva Naturale del torrente Orba
Parco uviale del Po tratto vercellese/
alessandrino e Riserva Naturale del torrente Orba
Parco uviale del Po tratto vercellese/
alessandrino e Riserva Naturale del torrente Orba
–
Riserva Naturale Speciale di Fontana Gigante
–
–
–
–
–
–
–
Region Municipality Locality Author Year of
collection
Reserve
73
On the Italian distribution of Dolomedes plantarius
national legislation, the preservation of natural population
of D. plantarius highly depends from the protection of oth-
er wetland species targets of conservation (i.e. amphibians
and birds), with similar ecological requirements.
Therefore, if from one side we emphasize the impor-
tance of umbrella species in the preservation of D. planta-
rius in Italy, from the other we underline the need of a de-
tailed understanding of the ecological requirements of this
species in order to optimize conservation efforts. Moreo-
ver, we advocate specic monitoring of the Italian popu-
lations, aiming to assess their conservation status and to
deepen the knowledge on the distribution in Italy of this
species of elevated conservation concern.
Acknowledgments – We are very thankful to Giovanni Soldato,
Daniele Seglie, Mauro Paschetta, Stefano Mammola, Sergio Fa-
sano, Massimo Evangelista, Nestor Vinals, who were involved
in the sampling activities. We are grateful to Fulvio Gasparo
and Alessio Trotta for checking their private collections. Spe-
cial thanks are due to Parco uviale del Po tratto vercellese/ales-
sandrino e Riserva Naturale del torrente Orba, for the logistic
support.
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Original data
Literature data
Uncertain records
(before 1930)
100 1000 200 km
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