First records of two new silverfish species (Ctenolepisma longicaudatum and Ctenolepisma calvum) in Slovakia, with checklist and identification key of Slovak Zygentoma

Abstract

In recent years, introduced synanthropic species of the order Zygentoma (especially Ctenolepisma longicaudatum and C. calvum ) have begun to spread in Central Europe. The two above-mentioned non-native species of silverfish have also recently been confirmed in Slovakia. This paper aims to comment on the occurrence of the two non-native species in Slovakia, to compile an identification key for all (i.e. also native) Slovak silverfish species and establish local species names.

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Vol.:(0123456789)
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Biologia
https://doi.org/10.1007/s11756-023-01526-z
ORIGINAL ARTICLE
First records oftwo new silverfish species (Ctenolepisma
longicaudatum andCtenolepisma calvum) inSlovakia, withchecklist
andidentification key ofSlovak Zygentoma
FrantišekBednár1 · VladimírHemala2 · TomášČejka3
Received: 24 April 2023 / Accepted: 9 September 2023
© The Author(s) 2023
Abstract
In recent years, introduced synanthropic species of the order Zygentoma (especially Ctenolepisma longicaudatum and C.
calvum) have begun to spread in Central Europe. The two above-mentioned non-native species of silverfish have also recently
been confirmed in Slovakia. This paper aims to comment on the occurrence of the two non-native species in Slovakia, to
compile an identification key for all (i.e. also native) Slovak silverfish species and establish local species names.
Keywords Alien species· Synanthropic pest· Lepismatidae· Nicoletiidae
Introduction
Zygentoma is an order of insects currently included in the
class Insecta, consisting of about 650 species and six fami-
lies (Robla etal. 2023), encompassing silverfish or fishmoths
and firebrats. Silverfish (Lepismatidae) are small arthropods
feeding on cellulose-based material. The last common ances-
tor with the remaining Dicondylia dates back more than
400million years (Misof etal. 2014).
Their last common ancestor dates over 400million years
ago (Misof etal. 2014). The order includes the so-called
silverfish or fishmoths and the firebrats belonging to the
family Lepismatidae, which are small arthropods feeding
on cellulose-based materials (e.g. Pothula etal. 2019).
Silverfish are indoor pests in homes, offices, museums,
and galleries, causing harm to objects such as paper, books,
photographs, and wallpaper (Trematerra and Pinniger 2018).
In particular, the grey silverfish (Ctenolepisma longicau-
datum) is receiving increasing attention as a pest of cultural
heritage in collections worldwide. In museums, archives
and libraries, C. longicaudatum is a recognised pest that has
damaged many objects in recent years. However, according
to some authors (e.g. Querner and Sterflinger 2021, 2022), it
requires high humidity (> 70% RH), so this species can only
damage paper-based materials in humid areas. Although
such risks are known for Lepisma saccharinum, the species
seldom causes damage to objects. In homes, most silverfish
(Lepismatidae) are not true pests but nuisance animals.
At the moment, eleven species are regularly recorded in
Central Europe. Only six of them are recorded in Slova-
kia: the common silverfish Lepisma saccharinum Linnaeus,
1758; the firebrat Thermobia domestica Packard, 1873; Ate-
lura formicaria Heyden, 1805 (species living in ant nests);
and three recently introduced species: the invasive grey or
long-tailed silverfish Ctenolepisma longicaudatum Escher-
ich, 1905, the four-lined silverfish Ctenolepisma lineatum
(Fabricius, 1775), and C. calvum (Ritter 1910). The exhaus-
tive distribution of L. saccharinum in Europe was reviewed
by Claus etal. (2022) with emphasis on its populations in
redwood ant nests (Formica rufa group), although it is more
common in buildings. Atelura formicaria is mainly restricted
to habitats outside buildings (Christian 1994), while all other
species are mostly related to human activity and found in
interiors. Ctenolepisma lineatum is also found outside build-
ings in some European countries, a facultative synanthropic
species. Further, five species were not recorded in Slovakia
* Tomáš Čejka
t.cejka@gmail.com
František Bednár
bednarfero@gmail.com
1 Lániky 271/26, SK-03491Švošov, Slovakia
2 Jalovec 32, SK-03221Bobrovec, Slovakia
3 Institute ofBotany, Plant Science andBiodiversity
Center, Slovak Academy ofSciences, Dúbravská cesta 9,
SK-84523Bratislava, Slovakia

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until now: Coletinia maggi (Grassi, 1887) recorded from
Austria (Christian 1993) and Hungary (Paclt and Christian
1996), Nicoletia phytophila Gervais, 1844 recorded from
Germany (Weidner 1983) and Switzerland (Gilgado etal.
2021), and three species recorded only from Germany (see
Weidner 1983): Stylifera impudica Escherich, 1905, Gas-
trotheus ceylonicus(Paclt, 1974) and Ctenolepisma roths-
childi Silvestri, 1907. Still, these five species are not known
as common insects in homes and buildings.
The spread ofnon‑native Lepismatidae inEurope
Recent years have witnessed an increase in synanthropic
Lepismatidae species in Central Europe, with new species
being introduced and spreading across the continent (e.g.
Christian 1993; Kulma etal. 2021):
Ctenolepisma longicaudatum, an invasive silverfish spe-
cies, has been passively introduced to most European terri-
tories (for details on its spread up to 2021, see Kulma etal.
2021).
Ctenolepisma calvum – its origin and native range are
unresolved. The first reports of C. calvum came from Ceylon
(Ritter 1910; Crusz 1957), followed by Guyana and Cuba,
where it was reported as a common house lepismatid by
Wygodzinsky (1972). The first European reports came from
Chemnitz, Germany (Landsberger and Querner 2018) and
Norway (Hage etal. 2020), although authors use no appro-
priate microscopic characters to identify this species con-
clusively. For details on the species spread up to 2021, see
Kulma etal. (2022).
Ctenolepisma lineatum is native to the warmer regions of
Central Europe and the North Mediterranean basin (Molero-
Baltanás etal. 2012). However, the species reached other
parts of the world through trade and transport (for details
on its spread in Europe up to 2020, see Hage etal. (2020).
History ofresearch onZygentoma inSlovakia
The first works on Zygentoma from the territory of today’s
Slovakia appear only at the end of the 19th century. In
this period, zoologists paid little attention to the faunistic
research of silverfish in Slovakia. The earliest faunistic data
from the territory of present-day Slovakia can be found in
the works of the Austro-Hungarian zoologist Tömösváry
(1884). At the end of the 19th century, Uzel (1891, 1897,
1898) contributed to the knowledge of the embryonic and
postembryonic development of Zygentoma. Petricskó (1892)
reports the occurrence of C. lineatum from the vicinity of
Banská Štiavnica. Vellay (1899) was the last to publish his
faunistic findings on Zygentoma in the iconic work Fauna
Regni Hungariae at the end of the 19th century.
Faunistic research afterWorld War II
Apart from a record of Kratochvíl (1945), who reported
C. lineatum from Slovakia, no one systematically studied
silverfish until the 1950s. Paclt (1951) reports a record of
A. formicaria from Bratislava. Paclt (1956) reports a single
locality and a single specimen of C. lineatum from south-
western Slovakia (regional name Žitný ostrov). Paclt (1959)
published a summary work on Slovak Zygentoma, listing
L. saccharinum, C. lineatum, and A. formicaria. Later,
he also published two important monographical works on
Zygentoma: the first one on the family Nicoletiidae (Paclt
1963) and the second one on the remaining families Lepi-
dotrichidae, Maindroniidae and Lepismatidae (Paclt 1967).
Ctenolepisma lineatum was also reported in Ivanka pri
Dunaji in 1966 (Paclt 1979), where it was recorded again
in 2021–2023 (V. Hemala, unpublished data). In 1975, a
faunistic survey of greenhouses in Bratislava was carried out
by Krumpál etal. (1997). Their paper only mentions the spe-
cies C. lineatum from the palm greenhouse of the Botanical
Garden in Bratislava. Some records of A. formicaria were
given in works focused primarily on other myrmecophilic
arthropods, e.g. in Pekár (2004) as the observation during
the study of ant-eating Zodariidae spiders or in Majzlan’s
(2009) study of the occurrence of the ant cricket Myrme-
cophilus acervorum (Panzer, 1799) in Slovakia. Majzlan’s
(2009) records of A. formicaria were also cited in the later
actualisation of the Slovak occurrence of M. acervorum in
Franc etal. (2015). Rusek (1977) provided the first check-
list of Czechoslovak Zygentoma, where Thermobia domes-
tica (Packard, 1837) was also listed for all parts of former
Czechoslovakia, including Slovakia. However, these records
were not found in any work published before 1977. It is pos-
sible that T. domestica was only collected and preserved but
not published due to considering it a common species. This
work aims to comment on the records of two new species for
Slovakia, compile an identification key and establish local
species names.
Materials andmethods
Morphological study
Preserved and living specimens were studied at differ-
ent magnifications without any treatment with the help
of a ZEISS Stemi 305 stereo microscope (Carl Zeiss AG,
Oberkochen, Germany) and Olympus BH2-BHT research
upright microscope (Olympus Corporation, Shinjuku,
Tokyo, Japan). Photographs were taken using a custom-
made microscope based on ZEISS AMPLIVAL research
upright microscope (VEB Carl Zeiss JENA, Jena, Deutsche
Demokratische Republik) body equipped with Mitutoyo

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M Plan APO objectives (Mitutoyo Corporation, Sakado,
Japan) and Canon EOS80D digital camera (Canon Inc.
Operations, Ohta-ku, Tokyo, Japan) and by Keyence VHX-
7000N equipped with VH-ZST objectives (Keyence Cor-
poration, Osaka, Japan). Photographs were focus-stacked
using Helicon Focus Software (HeliconSoft Helicon Soft
Ltd., Kharkiv, Ukraine). Individuals of both species were
identified using available identification keys (Theron 1963;
Wygodzinsky 1972; Molero-Baltanás etal. 2000, 2015; Aak
etal. 2019; Kulma etal. 2022).
Results
Considering the records of new species, six species of sil-
verfish currently occur in Slovakia, three of which are native
to the Slovak fauna (Table1).
Ctenolepisma longicaudatum Escherich, 1905
Ctenolepisma longicaudatum (Figs.1 and 2) was recorded in
the washrooms of the manufacturing building in Dolný Kubín-
Mokraď, Slovakia, on November 14, 2017 (iNat ID: https://
www. inatu ralist. org/ obser vatio ns/ 88046 78; accessed on 05
January 2023), and consequently at the same location and dif-
ferent places of the building on December 13, 2018 (iNat ID:
https:// www. inatu ralist. org/ obser vatio ns/ 19155 466; accessed
on 05 January 2023); October 19, 2021 (iNat ID: https:// www.
inatu ralist. org/ obser vatio ns/ 98730 948; accessed on 05 January
2023); September 7, 2022 (iNat ID: https:// www. inatu ralist.
org/ obser vatio ns/ 14549 7900; accessed on 05 January 2023);
December 26, 2022 (iNat ID: https:// www. inatu ralist. org/ obser
vatio ns/ 14518 2284; accessed on 05 January 2023); January
05, 2023 (iNat ID: https:// www. inatu ralist. org/ obser vatio ns/
14589 1809; accessed on 05 January 2023); these represent
the first documented records for Slovakia. The identification
of the first specimen, shown in Fig.1, was suggested by Nikola
Szucsich on iNaturalist (n.d.) (https:// www. inatu ralist. org) and
consequently confirmed by the authors based on morphologi-
cal characters presented in Figs.2, 3, and 4.
Ctenolepisma calvum (Ritter, 1910)
On June 11, 2021, C. calvum was spotted and caught in a
family house bathroom in Švošov, Ružomberok District,
Slovakia (iNat ID: https:// www. inatu ralist. or g/ obser vatio ns/
10675 1642; accessed on 05 January 2023) (Fig.5). Since
then, it has been spotted many times, for instance, on March
6, 2022 (iNat ID: https:// www. inatu ralist. org/ obser vatio ns/
10824 7596; accessed on 05 January 2023). This record rep-
resents the first documented record for Slovakia. The first
specimen was identified, and Nikola Szucsich confirmed
consequent findings on iNaturalist (n.d.) (https:// www. inatu
ralist. org). Figures6 and 7 present detailed images of speci-
mens caught at the same site, and Fig.8 illustrates a com-
parison of scales of both C. longicaudatum and C. calvum.
The identification of the first specimen, shown in
Fig.5, was suggested by Nikola Szucsich on iNatural-
ist(n.d.) (https:// www. inatu ralist. org) and consequently
confirmed by the authors based on morphological characters
presented in Figs.6 and 7.
Key tothespecies ofZygentoma withconfirmed occurrence
inSlovakia
This key is partly adapted from the key provided by Molero-
Baltanás etal. (2000) with the addition of C. calvum
Fig. 1 First record of Ctenolepisma longicaudatum, Nov 14, 2017,
Dolný Kubín-Mokraď, Slovakia, Photo by F. Bednár
Fig. 2 Dorsal and ventral view of Ctenolepisma longicaudatum,
December 26, 2022, Dolný Kubín-Mokraď, Slovakia, note truncated
antenna, cerci and median filament, Photo by F. Bednár

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according to the morphological diagnosis provided by
Kulma etal. (2022). The morphological terminology is
reviewed according to the morphological terms broadly used
in Molero-Baltanás etal. (2012) and the most recent works
on Zygentoma taxonomy and morphology (e.g. Molero
etal. 2018; Molero-Baltanás etal. 2022; Smith 2017; Smith
and Mitchell 2019) (Fig.9). Species with unconfirmed but
possible occurrences in Slovakia are mentioned in square
brackets. Zygentoma can be confused with members of
Microcoryphia by the lay public. Still, the main difference
Fig. 3 Size comparison of vari-
ous specimens of Ctenolepisma
longicaudatum, first three
from left Feb 26, 2023, right,
December 26, 2022, Dolný
Kubín-Mokraď, Slovakia, note
some truncated antenna, cerci
and median filament, Photo by
F. Bednár
Fig. 4 Ctenolepisma longi-
caudatum: a head dorsal view
where the cephalic tufts of
macrosetae (red arrow) and the
setal collar of the pronotum
(black arrow) are visible (upper
left), b head ventral view show-
ing labial palps (visible at the
bottom of the photo), c dorsal
view of abdomen showing
lateral bristle combs – infralat-
eral (blue arrows), lateral (green
arrows), sublateral (white
arrows), note all three types of
bristle combs on urotergites V
and VI (middle left), styli of
the abdominal sternites VIII
(yellow arrow) and IX (orange
arrow) are also visible, d ventral
side of the posterior part of the
female abdomen showing bases
of cerci, median filament and
two pairs of abdominal styli of
the abdominal sternites VIII
(yellow arrow) and IX (orange
arrow) (middle right), e detail
of a compound eye (lower left),
f micro photos of scales (lower
right), December 26, 2022,
Dolný Kubín-Mokraď, Slovakia,
Photo by F. Bednár

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is the absence of any jumping mechanism in Zygentoma (e.g.
Mendes 2002) and other characters: (a) eyes large, strongly
conspicuous and touching each other in Microcoryphia and
smaller, inconspicuous or absent in Zygentoma; (b) absence
of ocelli in Zygentoma (except the family Tricholepidiidae);
(c) maxillary palpus consists of 7 segments in Microcor-
yphia but of 5–6 segments in Zygentoma; (d) praetarsi with
two claws in Microcoryphia and three claws in most of
Zygentoma (some genera of Zygentoma have also two claws;
e.g. Hyperlepisma Silvestri, 1932, Mormisma Silvestri,
1938, and some other deserticolous genera); (e) metacoxae
with styli in Microcoryphia but without styli in Zygentoma;
(f) body more arched in Microcoryphia but more flattened in
Zygentoma and (g) middle caudal filament always strongly
longer than lateral two in Microcoryphia but inconspicu-
ously longer or of the same length as lateral two in Zygen-
toma (see Kratochvíl 1959).
Identification key ofSlovak species ofZygentoma
(For morphological structures, see Fig.9)
1. Eyes absent. Scales present or not (family Nicoletii-
dae)….…….……… ………... …...............………….……. 2
Eyes present. Scales always present (family Lepismati-
dae)……… …………….…..............................….….….… 4
2. Body short, spindle-shaped. Thorax broader than the
abdomen. Golden scales. Myrmecophilic……… ………
……… ……… ……… …......................…Atelura formicaria
Body elongated and cylindrical. Thorax as broad as the
abdomen. Scales absent. Often without pigmentation…. 3
3. Urosternites I–VII divided into two lateral coxites and one
median sternite................................…[Nicoletia phytophila].
Only urosternite I divided. Urosternites II–VII not divided
and composed by a single plate…….… ….[Coletinia maggi]
4. Macrosetae smooth, split into two or three ends apically.
Head without tufts of macrosetae; few frontal setae arranged
in irregular rows. Pronotum without a setal collar. Male
paramera present………........... .……Lepisma saccharinum
Macrosetae barbed. Head with tufts of abundant macrosetae
(Figs.4a and 7a). Pronotum with a setal collar (a row of
macrosetae inserted on the anterior margin; see Figs.4a and
7a). Male paramera absent……… ……… ……… ………. 5
5. Urotergites with at most 2 + 2 bristle combs of macro-
setae……… ……….......................…Thermobia domestica
At least urotergites II–V with 3 + 3 bristle combs of mac-
rosetae (genus Ctenolepisma)….…...........................…… 6
6. Urotergite X short, subtriangular with a convex posterior
border. Three pairs of abdominal styli in adults. Tibiae with
lanceolate scales. Femora with lanceolate or subtriangular
scales on their inner side. Anterior mesonotal trichobothria
inserted in the second last lateral combs….........................
..................................................…. Ctenolepisma lineatum
Urotergite X trapezoidal, with straight or nearly straight pos-
terior border. One or two pairs of abdominal styli. Tibiae
without scales. Femora with rounded scales on their inner
side. Anterior mesonotal trichobothria inserted in the third
last lateral combs. Anthropophilic……… ……… ………. 7
7. Both sexes with two pairs of styli when adults (Figs.2,
3 and 4d). Urotergite VI with 3 + 3 combs of macrosetae.
Without pigment or scarcely yellowish pigmented, but
dorsal scales usually dark greyish and with very dense
ribs. Antennae and caudal filaments, when intact, as long
Fig. 5 First-recorded individual of Ctenolepisma calvum, June 11,
2021, Švošov, Slovakia, Photo by F. Bednár
Fig. 6 Dorsal and ventral view of Ctenolepisma calvum, March 6,
2022, Švošov, Slovakia, note truncated antenna, cerci and median
filament, Photo by F. Bednár

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or longer than the body length……… ……… ……..…
…..…Ctenolepisma longicaudatum (Figs.1, 2, 3, 4 and 8)
Both sexes with only one pair of abdominal styli when
adults (Fig.6). Urotergite VI with 2 + 2 combs of macro-
setae. Uniformly whitish with a slightly yellowish-brown
or grey pigment in some appendages. Dorsal scales almost
hyaline and mostly with less dense ribs. The length of the
antennae is an intraspecific variable but usually not longer
than body length when intact. Two lateral caudal filaments
approximately 2/3 of the body length, the middle caudal
filament is approximately as long as the body when intact
…….........…….Ctenolepisma calvum (Figs.5, 6, 7 and 8)
Fig. 7 Ctenolepisma calvum:
a dorsal head view where the
cephalic tufts of macrosetae
(red arrow) and the setal collar
of the pronotum (black arrow)
are visible (upper left), b ventral
head view where the cephalic
tufts of macrosetae (red arrow)
are visible (upper right), c dor-
sal view of abdomen showing
lateral bristle combs – infralat-
eral (blue arrows), lateral (green
arrows), sublateral (white
arrows), note only two pairs
of macrosetae on urotergite VI
(blue and white arrow), one
of the diagnostic characters,
which separates C. calvum
from C. longicaudatum, styli
of the abdominal sternite IX
(yellow arrow) are also visible
(middle left), d ventral side of
the posterior part of the female
abdomen showing one pair of
abdominal styli (yellow arrow),
e detailed ventral view showing
lateral bristle combs, f micro
photo of scales (lower right),
December 26, 2022, Dolný
Kubín-Mokraď, Slovakia, Photo
by F. Bednár
Fig. 8 Comparison of scales,
left Ctenolepisma calvum, right
Ctenolepisma longicaudatum,
Photo by F. Bednár

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Discussion
In particular, two non-native silverfish species (C. longicauda-
tum and C. calvum) have spread across Europe recently (Kulma
etal. 2021, 2022; Querner etal. 2022) solely due to human activ-
ity. As these insects cannot survive the winter in most Central
and Northern European climates, suitable living conditions are
restricted to houses, museums, warehouses, archives and other
buildings (Brimblecombe and Querner 2021; Querner etal.
2022). The frequency of new introductions has increased in
recent years, so further spread should be expected. Both spe-
cies are strictly synanthropic; no outdoor occurrences have been
published, so climate does not limit their distribution. For this
reason, they have also recently become successfully established
in northern Europe (Aak etal. 2019; Sammet etal. 2021).
We agree with Kulma etal. (2021) that the current distribu-
tion of C. longicaudatum in Europe, in particular, is underesti-
mated, as supported by findings published on social platforms
(e.g. iNaturalist.org). Further collaboration between local
entomologists, citizens and pest control services is essential
to confirm the range of this non-native species.
The first record of C. longicaudatum in 2017 corresponds
with records in Czechia, where the first occurrence of a pop-
ulation of C. longicaudatum was recorded in warehouses and
around office buildings (Kulma etal. 2018). Subsequently,
C. longicaudatum was recorded throughout the country
over the next three years. As expected, dwellings emerged
as the main habitats of the species, as confirmed by recent
data from several countries. This phenomenon is known, for
example, in the Faroe Islands, the Netherlands and Norway,
where the species has become a notable household species
(Thomsen etal. 2019; Querner etal.2022; Hage etal. 2020).
Four years later (2021), the silverfish C. calvum was also
recorded in Slovakia, again in the same year as in the Czech
Republic (Kulma etal. 2021). Since we assume that C. cal-
vum spreads similarly to C. longicaudatum, it is possible
that C. calvum was overlooked because it may have been
mistaken for the juvenile stages of C. longicaudatum.
The extent of damage and current distribution in museums
and archives in Slovakia has yet to be discovered, so it would be
advisable to undertake more intensive mapping and monitoring
(e.g. using sticky traps) to ascertain populations’ current distri-
bution and status as quickly as possible. First, it is advisable to
Table 1 Checklist of Slovak Zygentoma
Explanations: Checklist of Slovak Zygentoma; column 1: scientific name, common names in SK, CZ, UK, and DE, new proposed Slovak names
are marked with *; column 2: references from Slovakia; column 3: status of inclusion in the previous Czechoslovak checklist
Taxa References Listed in Rusek (1977)
Lepismatidae
Ctenolepisma calvum(Wygodzinsky, 1910)
*švehla lysá (SK)
Ghost Silverfish (UK)
Geisterfischen (DE)
this paper no
Ctenolepisma lineatum (Fabricius, 1775)
*švehla pásikavá
rybenka jižní (CZ)
Four-lined Silverfish (UK)
Kammfischchen (DE)
Petricskó (1892); Kratochvíl (1945); Paclt (1956, 1959, 1979);
Krumpál etal. (1997)
yes
Ctenolepisma longicaudatumEscherich,
1905
*švehla dlhochvostá (SK)
Long-tailed Silverfish, Grey Silverfish,
Urban Silverfish (UK)
Papierfischchen (DE)
this paper no
Lepisma saccharinumLinnaeus, 1758
švehla striebristá (SK)
rybenka domácí (CZ)
Tömösváry (1884); Vellay (1899); Stach (1922, 1929); Štys (1977)yes
Thermobia domestica(Packard, 1837)
švehla skleníková (SK)
rybenka skleníková (CZ)
Firebrat (UK)
Ferianc (1975);Rusek (1977)yes
Nicoletiidae: Atelurinae
Atelura formicariaHeyden, 1855
švehla mravenisková (SK)
rybenka mravenčí (CZ)
Kleines Ameisenfischchen (DE)
Stach (1922, 1929); Paclt (1951, 1959); Pekár (2004); Majzlan
(2009); cited in Franc etal. (2015)
yes

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target archives, museums and libraries, for which these species
pose the greatest threat concerning the valuable items deposited
by these institutions (Querner etal. 2022).
Since Paclt’s work (Paclt 1959), no comprehensive work or
species list of Slovak silverfish (specifically of the family Lepis-
matidae) has been published, so we decided to fill this gap of
more than sixty years. Since Kratochvíl’s identification key for
identifying Zygentoma and Microcoryphia of former Czechoslo-
vakia (Kratochvíl 1959), keys were never actualised or provided
for Slovakian Zygentoma until now. Some useful but old keys
exist for British Delaney (1954) and Polish species (Stach 1955).
Notes ontheidentification ofthespecies
During microscopic studies of specimens, we noticed
that the rib density of scales varies between the species.
Therefore, we photographed various shapes and sizes of
Fig. 9 Morphological features
of the family Lepismatidae
exemplified in Ctenolepisma
longicaudatum

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scales under a brightfield microscope. Selected photos
of scales are presented in Fig.4. and Fig.7. Comparison
of C. calvum and C. longicaudatum scale rib densities
are shown in Fig.8. As can be seen, C. longicaudatum
has significantly higher rib density than C. calvum (14
vs. 43 ribs per 100μm for larger scales and 41 vs. 74
ribs for smaller scales). However, we would not like to
present exact numbers as the scales are from various
body parts and only from two specimens. Further study
is required; however, the rib density is so distinct that we
have included it in the key. In future studies, this could
be a helpful identification character for separating other
members of Lepismatidae.
Although C. calvum is distinctly smaller than C. longi-
caudatum in Slovakia, according to our studied specimens
(maximum length 8mm in C. calvum and 11mm in C. lon-
gicaudatum), the body length of C. calvum can vary, and it
can reach 12mm, as it was discovered in Japan by Shimada
etal. (2022).
The presence of two pairs of styli in males of C. lon-
gicaudatum (Fig.4d) is also an important character dis-
tinguishing the species from another visually similar
synanthropic species, C. targionii (Grassi and Rovelli,
1889), males of which have only one pair of styli (e.g.
Molero-Baltanás etal. 2015). Nevertheless, this Medi-
terranean species was introduced only in the USA and
India until now (Wygodzinsky 1972; Hazra and Mandal
2007), and its spreading within Europe northwards from
the Mediterranean area is still unknown.
Acknowledgements We would like to express our gratitude to the
reviewers for their dedication and efforts. We are especially thankful
to reviewer #2 for their insightful, beneficial, and thorough feedback
and suggestions, which extensively enhanced the manuscript’s origi-
nal content. We express our gratitude to Ľubomír Haluška and Matúš
Gonšor for collecting some specimens and Nikolaus Szucsich for iden-
tifying the specimens on the iNaturalist website. We would like to
acknowledge Ľubomír Vidlička from the Institute of Zoology, Slovak
Academy of Sciences, for his invaluable help in finding historical data
on the distribution of silverfish in Slovakia.
Funding Open access funding provided by The Ministry of Education,
Science, Research and Sport of the Slovak Republic in cooperation
with Centre for Scientific and Technical Information of the Slovak
Republic The research was financially supported by the project agen-
cies VEGA (Scientific Grant Agency of the Ministry of Education,
Science, Research and Sport of the Slovak Republic and the Slovak
Academy of Sciences): project VEGA no. 2/0108/21 and APVV (The
Slovak Research and Development Agency): project no. APVV-19-
0134 and APVV-21-0386.
Declarations
Ethics approval and consent to participate Not applicable.
Consent for publication Not applicable.
Conflict of interest The authors declare no conflict of interest.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
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permitted by statutory regulation or exceeds the permitted use, you will
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