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Stylostomes of the trombiculid mite larvae Neotrombicula pomeranzevi (Schluger), Hirsutiella zachvatkini (Schluger), Miyatrombicula esoensis (Sasa and Ogata) and Euschoengastia rotundata (Schluger) (Acariformes: Trombiculidae), formed in the host skin during feeding of the parasites on their natural hosts (voles) were studied histologically and histochemically. A stylostome is a variously shaped tube formed of solidified mite saliva that extends from the mouthparts of the parasite through the epidermis into the dermis of the host, and allows the mite to obtain its liquid food. The first step of stylostome formation is deposition of an eosinophilic cone, to which the larva's chelicerae are glued. Organization of the stylostome depends on the mite species, and its walls may show weakly expressed longitudinal or transverse stratification. Histochemically, the stylostome is composed of complex glycoprotein with varying tinctorial properties through the width or the length of the stylostome's walls. Beneath the distal end of the stylostome, irrespectively of its localization either in the epidermis or in the dermis of the host, a feeding cavity is formed as a result of the action of the hydrolytic components of the mite's saliva forced through the stylostome into the wound. An inflammatory dermal reaction of moderate intensity is evolved during larval feeding and stylostome formation. It is manifested by the infiltration of the foci with neutrophiles, lymphocytes and macrophages and by dilation of capillaries of the terminal vessel bed and filling them by erythrocytes and other blood elements. Around the stylostome, necrosis of the epidermal cells occurs, leucocytes come to the damaged area and fuse with the necrotic epidermal cells, leading to the formation of the large scabs on the surface of the host's skin. In the case of E. rotundata, single capsules having a terminal opening and containing feeding larva are formed on the abdomen of the hosts. The walls of the capsules are composed of the mite's saliva flowing upon the surface of the host's skin. At the bottom of the capsule, a stylostome perforating the epidermis is also present.

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The characters of the life cycle and demographic processes of Ixodes ricinus (L., 1758), (Acari: Ixodidae) populations in the North-West of Russia were studied using methods of the long-term observations of ticks in insets in the natural biotopes (2013–2018). It was found that in the North-West of Russia, I. ricinus had a long period of seasonal activity (from April until October) and a long calendar age. Larvae, nymphs, as well as adults of both sexes can remain active for up to 12–15 months when they meet with appropriate host and feed successfully. Up to 9±0.8% of adults can overwinter twice and remain active until the end of June of the third year of their life (23 months). The I. ricinus tick at every developmental stage forms a certain sub-group of population in August–September. Due to the highly prolonged life the larvae, nymphs and females of I. ricinus are able to feed, and the females can lay eggs during their entire active period from April till October. At the same time, larvae and nymphs that feed from April to June molt in the year of feeding, and their development proceeds according to a three-year scenario. The females feeding from April to June can produce offspring during the same season, thus forming a 3-year developmental cycle. By contrast, all individuals (larvae, nymphs and females) feeding from July to October molt to the next stage in August–September of the following year. Females feeding in July–September can lay eggs both in the year of feeding and after winter diapause. This leads to an increase in the duration of the basic 3-year developmental cycle and its complexity. If the ticks molted the next year after feeding only once in the life cycle, the whole life cycle would increase by a year. If they did it in every developmental stage, then the life cycle would increase by three years. Thus, the total duration of development of ticks of one generation may last from 3 to 6 years. Some adult ticks (not more than 9±0.8% in the population) can remain active until the end of June of the seventh season.

The stylostome of larvae of the trombiculids Leptotrombidium scutellare (Nagayo et al.), Leptotrombidium fletcheri (Womersley et Heaslip) and Leptotrombidium deliense (Walch) was studied experimentally at different time intervals after larval attachment using the histological method. The stylostome of these species has the same organization and belongs to the epidermal combined with the mixed type, developing more in width than in length. Neither transverse nor conspicuous longitudinal layers are present within the stylostome walls, which stain predominantly in red with Azan, also showing longitudinal portions with blue staining. Larvae tend to attach closely to each other and scabs, consisting of the hyperkeratotic epidermal layers fusing with migrating inflammatory cells, develop around the attachment sites. The dermis shows inflammatory foci with dilated capillaries and inflammatory cells inserting in the connective tissue layer underneath the stylostome. The feeding cavity, which is moderately expressed, may be found either in the epidermis or in the dermis. It contains inflammatory cells and their debris in the liquefied host tissues. The stylostome length depends on the character of the attachment site (the thicker epidermis or scab the longer the stylostome), and does not directly correspond to the stages of larval feeding. Nevertheless, at the 48-h time interval, nearly all attached larvae are found to be fully fed and their midgut cells are filled with nutritional globules.