Members of the family Rhinonyssidae are tiny hematophagous endoparasitic mites that inhabit the nasal cavities of birds and can cause trauma to their hosts. Traditionally, identifying species in this group has relied on observing their morphometrical characteristics. Nevertheless, determining species within this particular group has become more challenging due to the rising number of newly discovered species. Moreover, the morphometrical traits vary depending on the specific genus or group of species being studied. In this study, the complete internal transcribed spacer ITS1, 5.8S rDNA, and ITS2 regions of the ribosomal DNA from eighteen species of rhinonyssid mites belonging to four genera were sequenced to assess the utility of this genomic region in resolving taxonomic questions in this group and to estimate the phylogenetic relationships among the species. Mites were collected by dissecting the nasal cavities of birds under a stereomicroscope. Specimens used for morphometrical analyses were cleared in 85% lactic acid for 1–48 h and mounted in Hoyer’s medium. Other specimens were preserved at −20 °C for molecular studies. From the data obtained in this study, it can be concluded that a thorough review and an accurate morphometrical identification and determination of the discriminatory traits are needed in this group of mites. Moreover, although the ITS1–5.8S–ITS2 fragment solves different taxonomic and phylogenetic problems at the species level, it would be necessary to test new molecular markers, or even a combination of nuclear and mitochondrial markers or different domains of the nuclear 28S rDNA, to discover a reliable taxonomic situation for rhinonyssids.

Different morphotypes of Demodex from humans have been described. Among them, molecular studies have made it possible to discern between the Demodex folliculorum and Demodex brevis. Further studies showed two morphotypes of D. folliculorum harboured two different habits (human skin and human eyelashes), both of them with finger-shaped terminal opisthosoma difficult to differentiate and that can be assigned to D. folliculorum, Thus, a complete morphometric study of the species, which in this study are referred to as Demodex folliculorum species complex, was carried out. From this morphometric and meristic study two distinct morphological forms (short and long) could be identified within the Demodex folliculorum species complex. These forms differ significantly in four out of the six biometric parameters we analysed: gnathosomal length and width, podosomal width, and opisthosomal length. Moreover, a comprehensive survey of the two morphotypes from different habitats (skin and eyelashes), was carried out in young people of Southern Spain. Therefore, an analysis of 104 asymptomatic students, which were contact lens wearers, and the presence of D. folliculorum was carried out. A statistical analysis based on Bayesian zero inflated Poisson GLM has been applied to our sample data. For the age group considered (18-24 years old), the overall D. folliculorum prevalence for skin face or eye infections (at least one of them) was 19.31 % (51 people), with a statistically significant higher prevalence in males men. Furthermore, there is a slight statistical correlation between the presence of Demodex in silicone hydrogel soft contact lens wearers. This study confirms: i) the existence of two morphotypes of D. folliculorum that appear segregated due to the parasitization microhabitats,ii) a higher prevalence of mites in men than in women, iii) the existence of a high number of statistically supported double infections (skin-eyelashes). It also provides epidemiological data on the prevalence of long and short forms of D. folliculorum in a healthy young population.

Ticks are obligate hematophagous arthropods and major vectors of diverse bacterial, parasitic, and viral pathogens. They host complex microbial communities that critically influence their biology, fitness, and interactions with pathogens. Using 16 S rRNA gene amplicon sequencing at the amplicon sequence variant (ASV) resolution combined with co-occurrence network analysis, we characterized the bacterial communities of questing adult ticks collected in the Cazorla, Segura y Las Villas Natural Park (Jaén, Spain). A total of 83 adult ticks (27 males and 56 females) representing six sympatric species, Dermacentor marginatus ( n = 39), Haemaphysalis punctata ( n = 9), H. sulcata ( n = 15), Hyalomma lusitanicum ( n = 7), Ixodes ricinus s. l. ( n = 2), and Rhipicephalus bursa ( n = 11), were analyzed. After stringent quality filtering, 3.77 million high-quality reads were recovered and resolved into 407 ASVs. Due to the inherent resolution limits of the V3–V4 region for species-level discrimination, taxonomic assignments were conservatively consolidated at the genus level (101 bacterial genera). Across all tick species, the bacteriome was heavily dominated by Pseudomonadota (98.6%), with species-specific differences primarily driven by variation in obligate symbionts. Coxiella -associated ASVs predominated in multiple tick species, whereas H. lusitanicum exhibited strong dominance by Francisella and secondary representation of Candidatus Midichloria . Alpha and beta diversity analyses revealed distinct compositional patterns shaped by host identity, with lower dispersion observed in D. marginatus and R. bursa , and greater variability among Hyalomma and Haemaphysalis individuals. Spearman-based co-occurrence network analysis indicated a highly cooperative and modular structure (> 98% positive correlations) across tick species. Notably, dominant endosymbionts ( Coxiella , Rickettsia , and Francisella ) occupied peripheral or weakly connected positions within the networks. In contrast, ecological connectivity was governed by a distinct set of low-abundance taxa, including Roseomonas , Friedmanniella , Methylobacterium , Sphingomonas , Aureimonas , Conexibacter , Marmoricola , Mycobacterium , and Nocardioides , which acted as central hubs bridging network modules, a topology robustly validated by an independent, composition-aware (SparCC) reanalysis within the D. marginatus cohort. These comparative findings demonstrate a functional decoupling between abundance and connectivity in tick microbiomes, highlighting how the “rare microbiome” can drive the topological organization and potential stability of microbial communities across sympatric host species.