Synanthropic silverfish are the best-known and most widely distributed insects of the order Zygentoma. However, there is a great gap in the knowledge and confusion about the geographic distribution and the diagnostic characteristics that allow their identification. In this work, we provide an exhaustive and deep analysis of the most common 9 synanthropic silverfish of the world, combining previously published and newly derived morphological and molecular data. Updated descriptions of Ctenolepisma calvum ( Ritter, 1910) and Ctenolepisma (Sceletolepisma) villosum (Fabricius, 1775) are included, and morphological remarks, illustrations, and photographs of the remaining synanthropic species are provided to clarify their diagnosis and differentiation among them and from other free-living species. In addition, Ctenolepisma targionii (Grassi and Rovelli, 1889) is synonymized with C. villosum. A molecular phylogeny is presented based on the COI sequences of all the synanthropic species deposited in BOLD and GenBank, with 15 new sequences provided by this study. This has allowed us to detect and correct a series of identification errors based on the lack of morphological knowledge of several species. Moreover, 2 different lineages of Ctenolepisma longicaudatum Escherich, 1905 have also been detected. To help future studies, we also provide a taxonomic interpretation guide for the most important diagnostic characters of the order Zygentoma, as well as an identification key for all the Synanthropic studied species. Finally, an approximation of the global distribution of synanthropic silverfish is discussed. Several new records indicate that the expansion of these species, generally associated with the transport of goods and people, is still far from over.

Background: Various animal taxa have specialized to living with social hosts. Depending on their level of specialization, these symbiotic animals are characterized by distinct behavioural, chemical, and morphological traits that enable close heterospecific interactions. Despite its functional importance, our understanding of the feeding ecology of animals living with social hosts remains limited. We examined how host specialization of silverfish co-habiting with ants affects several components of their feeding ecology. We combined stable isotope profiling, feeding assays, phylogenetic reconstruction, and microbial community characterization of the Neoasterolepisma silverfish genus and a wider nicoletiid and lepismatid silverfish panel where divergent myrmecophilous lifestyles are observed. Results: Stable isotope profiling (δ¹³C and δ¹⁵N) showed that the isotopic niches of granivorous Messor ants and Messor-specialized Neoasterolepisma exhibit a remarkable overlap within an ant nest. Trophic experiments and gut dissections further supported that these specialized Neoasterolepisma silverfish transitioned to a diet that includes plant seeds. In contrast, the isotopic niches of generalist Neoasterolepisma silverfish and generalist nicoletiid silverfish were clearly different from their ant hosts within the shared nest environment. The impact of the myrmecophilous lifestyle on feeding ecology was also evident in the internal silverfish microbiome. Compared to generalists, Messor-specialists exhibited a higher bacterial density and a higher proportion of heterofermentative lactic acid bacteria. Moreover, the nest environment explained the infection profile (or the 16S rRNA genotypes) of Weissella bacteria in Messor-specialized silverfish and the ant hosts. Conclusions: Together, we show that social hosts are important determinants for the feeding ecology of symbiotic animals and can induce diet convergence.

The Mediterranean Basin is considered one of the most important hotspots of biodiversity in the European region. Many taxa exhibit high levels of speciation and endemicity in this area. This is the case of the myrmecophilous insects of the families Lepismatidae and Nicoletiidae (Insecta: Zygentoma) that are further assessed in this study using unpublished and bibliographic data. A complete checklist of all ant-associated silverfish occurring in the Mediterranean Basin is presented, together with an updated identification key and interesting new records for several countries. Considering all described Zygentoma species, the myrmecophilous silverfish of the Mediterranean area represent 28% of all ant-associated species of the world and about 35% of the studied area. Even with the scarce knowledge of Zygentoma in other biogeographic areas and with insufficient sampling in other continents, we conclude that the Mediterranean region, and neighbouring areas of the Western Palaearctic, represent the most important biodiversity hotspot of ant-associated Lepismatidae (about 30% of the myrmecophilous species of this family described in the world so far), while the highest diversity of myrmecophilous Atelurinae is linked to tropical regions.

Two new species of the genus Ctenolepisma Escherich, 1905 are described from Andhra Pradesh and Tamil Nadu, India: Ctenolepisma (Ctenolepisma) venkataramani sp. n. and Ctenolepisma (Ctenolepisma) udumalpetense sp. n. Their affinities with related species are discussed and a key to the Indian species of the genus is provided.

As a starting point for the revision of the genus Ctenolepisma Escherich 1905, the status of its type-species, Ctenolepisma lineata (Fabricius 1775), is clarified. In the present study, this species (originally described from Switzerland) is redescribed by means of many samples from several European countries and a neotype is designated. The constant presence of a third pair of abdominal styli in adult C. lineata s. str. leads to abandon the obsolete name C. lineata var. pilifera (Lucas 1840) for referring to a presumed non-typical variety of this species. The status of Lepisma pilifera Lucas 1840 is discussed, concluding that this name must be treated as a new synonym of Thermobia aegyptiaca (Lucas 1840). After our redefinition of the characters of C. lineata, an examination of many specimens of Ctenolepisma that were previously identified as C. lineata reveals that some of them are actually members of different taxa. This is the case for a species occurring in the Canary Islands, Northwest Africa, the Iberian Peninsula and the Balearic Islands. In this work this species is ascribed to Lepisma nicoletii Lucas 1846, which was described from Algeria and regarded as a synonym of Ctenolepisma lineata by Escherich; this species is now redescribed as Ctenolepisma nicoletii stat. res. This species differs from C. lineata in that it bears only two pairs of abdominal styli, and it also differs in the shape of the prosternum and femoral scales. Lepisma eatoni Ridley 1881, which was described from Morocco and the Canary Islands and subsequently regarded as synonym of C. lineata, is now synonymised with C. nicoletii.