NATURA SLOVENIAE 26(2): 41-44 Prejeto / Received: 29. 11. 2024 
FIELD NOTE Sprejeto / Accepted: 19. 12. 2024 
 
DOI: 10.14720/ns.26.2.41-44 
 
 Biotehniška fakulteta Univerze v Ljubljani in Nacionalni inštitut za biologijo, Ljubljana, 2024 
First record of the pill bug 
Armadillidium arcangelii 
Strouhal, 1929 (Crustacea: 
Isopoda) in Slovenia 
 
Miloš VITTORI, University of Ljubljana, Biotechnical 
Faculty, Department of Biology, Jamnikarjeva 
101, SI-1000 Ljubljana, Slovenia;  
E-mail: milos.vittori@bf.uni-lj.si  
 
Abstract. Numerous novel occurrences of 
Armadillidium arcangelii, a terrestrial isopod native to 
Italy, have been reported in recent years in 
synanthropic habitats across much of Europe. These 
records indicate that the species is rapidly spreading, 
likely via the transport of plants. On 21. 9. 2023, a male 
of this species was collected on turf near Seča on the 
Slovenian coast. This is the first record of A. arcangelii 
in Slovenia. The record is all the more relevant as  
A. arcangelii is a potential agricultural pest. 
 
Izvleček. Prva najdba pasavčka vrste 
Armadillidium arcangelii Strouhal, 1929 
(Crustacea: Isopoda) v Sloveniji – V zadnjih nekaj 
letih so v sinantropnih habitatih v različnih delih Evrope 
opazili kopenskega enakonožca, pasavčka vrste 
Armadillidium arcangelii, ki izvira iz Italije. To kaže na 
hitro širjenje te vrste, najverjetneje s transportom 
rastlin. Samca vrste A. arcangelii smo našli 21. 9. 2023 
na trati ob morju blizu Seče. To je prvo opažanje vrste 
A. arcangelii v Sloveniji. Najdba je pomembna tudi, ker 
je bila vrsta prepoznana kot potencialen škodljivec na 
poljščinah. 
 
Terrestrial isopod crustaceans (Oniscidea) are a 
substantial part of soil invertebrate fauna. Over the 
past decades, numerous species have been 
introduced to parts of the world where they had not 
been present previously (Sfenthourakis & Hornung 
2018). In certain regions of North America, the 
terrestrial isopod fauna may consist almost entirely 
of introduced species, predominantly of European 
origin (Szlavecz et al. 2018).  
Recently, an enigmatic Armadillidum species has 
been recorded from numerous locations in Europe 
and Britain, with most of these occurrences likely 
representing recent introductions. While some 
uncertainty remained regarding the identity of the 
species that is rapidly colonizing synanthropic 
habitats across Europe, its morphological features 
matched those of Armadillidium arcangelii Strouhal 
1929 (Noël et al. 2022), a species native to Italy 
(Schmalfuss 2003). In the past decade, these pill 
bugs have been collected and examined in the 
United Kingdom (Gregory 2014; Hughes et al. 
2024), Spain (Garcia & Cabanillas 2021), France, 
Greece, the Netherlands (Noël et al. 2022), and 
Belgium (De Smedt & Van Dijck 2023). Citizen 
science data on the iNaturalist platform 
(https://www.inaturalist.org/) suggest that it is 
likely present in several other European countries as 
well, including Austria, Croatia, Germany, Poland, 
and Portugal (Noël et al. 2022). Nevertheless, the 
identification of this species, now widespread in 
Europe, is provisional, as A. arcangelii is 
morphologically very similar to Armadillidium 
apenninorum and Armadillidium marmoratum, and 
some of these species names might be synonyms 
(Schmalfuss 2003; Noël et al. 2022; Hughes et al. 
2024). 
On 21. 9. 2023, a single adult male of a terrestrial 
isopod belonging to the genus Armadillidium was 
collected by the author of this field note on the 
Slovenian Adriatic coast (Fig. 1). The small, mottled 
pill bug was found under dead wood on a public turf 
along the shore near Seča (45.502944 N,  
13.589944 E; 5 m a.s.l.). Further examination of the 
habitus and male characters revealed that the 
isopod matches the descriptions of A. arcangelii. 
The isopod and its dissected appendages are kept 
in the author’s collection at the Department of 
Biology, Biotechnical Faculty, University of 
Ljubljana. 
Several features can be used to identify  
A. arcangelii. The species is relatively small, with 
females reaching 8–9 mm in length and males being 
smaller (Strouhal 1929; Noël et al. 2022). The 
colour, while variable, is usually mottled brown 
(Strouhal 1929; Noël et al. 2022; Fig. 1A). The 
antennal lobes are small, protruding, and rounded, 
and the dorsal margin of the frontal shield reaches 
slightly above the frontal edge of the cephalothorax 
(Fig. 1A, B). The proximal article of the flagellum of 
the second antenna is shorter than the distal article 
(Strouhal 1929; Fig. 1A). The lateral parts of the 
posterior margin of pereonite 1 are curved, not 
sharply bent (Fig. 1A). The pleotelson is triangular, 
with straight lateral edges and rounded tip (Strouhal 
1929; De Smedt & Van Dijck 2023; Fig. 1C). 
Diagnostic characters include the shape of the 
uropods (Strouhal 1929) and male characters, 
specifically the male pereopod 7 and pleopod 1 
(Garcia & Cabanillas 2021; Noël et al. 2022). The 
posterior edge of the uropod exopodite in both 
sexes is not rounded (Strouhal 1929; Fig. 1C). The 
exopodite of the male pleopod 1 ends in a triangular 
42 Miloš VITTORI: First record of the pill bug Armadillidium arcangelii in Slovenia / FIELD NOTE 
NATURA SLOVENIAE 26(2): 41-44 
distal lobe and the posterior edge of the exopodite 
bends near the distal end of the perispiracular area 
(Garcia & Cabanillas 2021; Noël et al. 2022;  
Fig. 1D). The tip of the male pleopod 1 endopodite 
curves outwards (Noël et al. 2022; Fig. 1E). The 
ventral edge of the ischium on the male pereopod 7 
is straight (Noël et al. 2022; Fig. 1F). 
 
Figure 1. Armadillidium arcangelii, male, collected near Seča, Slovenia. A – habitus; B – cephalothorax; C – pleotelson 
with uropods; D – pleopod 1 exopodite with a bent posterior edge (arrowhead); E – pleopod 1 endopodite with the tip 
curving outward (arrowhead); F – straight ventral edge of ischium (arrowhead) on pereopod 7. Scale bars: 1 mm (A); 
0.5 mm (B, C, F); 100 µm (D); 50 µm (E) (photo: M. Vittori). 
Slika 1. Armadillidium arcangelii, samec, nabran blizu Seče v Sloveniji. A – habitus; B – glavoprsje; C – pleotelzon z 
uropodi; D – eksopodit pleopoda 1 s pregibom na posteriornem robu (puščica); E – endopodit pleopoda 1 s konico, 
upognjeno navzven (puščica); F – raven ventralni rob ischiuma (puščica) na pereopodu 7. Merilca: 1 mm (A);  
0,5 mm (B, C, F); 100 µm (D); 50 µm (E) (foto: M. Vittori). 
Miloš VITTORI: First record of the pill bug Armadillidium arcangelii in Slovenia / FIELD NOTE 43 
NATURA SLOVENIAE 26(2): 41-44 
In Britain, initial reports came from greenhouses, 
but the species has since also been reported in 
garden centres (Hughes et al. 2024). In Spain, it 
was reported in habitats affected by human 
activities such as mining and industrial waste 
disposal near Madrid and Cádiz (Garcia & Cabanillas 
2021; Garcia & Rojas 2021). In France, the species 
occurs in synanthropic habitats outdoors, mainly 
close to the coast (Noël et al. 2022). In Belgium,  
A. arcangelii was recorded on the green roofs of the 
University of Hasselt, where it was collected on 
several occasions over the span of 4 years  
(De Smedt & Van Dijck 2023). 
The main route of the introduction of the species to 
several European locations was likely the transport 
of plants (Noël et al. 2022; De Smedt & Van Dijck 
2023; Hughes et al. 2024). While terrestrial isopods 
generally do not cause agricultural damage,  
A. arcangelii was recently identified as a potential 
agricultural pest in Italy, as it may feed on young 
melon plants (Fusaro et al. 2024). The species had 
not been known to affect crops before. 
As it had not been reported in Slovenia previously, 
despite extensive past research of the area 
(Potočnik 1984), and as it is known to have been 
introduced in other parts of Europe, A. arcangelii 
may have been introduced to Slovenia. 
Nevertheless, since Italian populations are relatively 
close, it is also possible that the species spread to 
Slovenia naturally, or that it was present in this area 
in the past, but never collected or recognized. Given 
its wide distribution and rapid spreading (Noël et al. 
2022), the finding of A. arcangelii in Slovenia had 
been expected. Considering previous checklists of 
the terrestrial isopod fauna of Slovenia (Vittori  
et al. 2023), recent records (Jakob et al. 2024), and 
the record of A. arcangelii reported here, there are 
currently 76 recorded species of Oniscidea in the 
country. 
 
Acknowledgments 
 
This work was supported by the University Infrastructural 
Centre »Microscopy of Biological Samples« at the 
Biotechnical Faculty, University of Ljubljana. 
 
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