# The Biology of Demodecid Mites (Trombidiformes: Demodecidae) and Their Parasitism in the Eurasian Beaver Castor fiber Linnaeus, 1758, with a Description of a New Species

## TL;DR

This study discovers two types of mites in beavers, one new species, and reveals unique biological traits in how these mites live and reproduce.

## Contribution

Describes a new mite species and confirms a universal pattern of demodecid mite parasitism in mammals.

## Key findings

- A new mite species, Demodex ovaportans, was found on hairless skin around the beaver's mouth.
- Demodex castoris was detected across the entire hairy skin of the beaver, confirming a universal parasitism pattern.
- Females of the new species carry eggs on their bodies, a previously unknown reproductive strategy in Demodecidae.

## Abstract

Two species of parasitic mites from the family Demodecidae were identified in the skin of the Eurasian beaver Castor fiber, each occupying distinct microhabitats. Also, representatives of a new species, Demodex ovaportans sp. nov., associated with hairless skin, mainly around the mouth, were found. In contrast, Demodex castoris, previously known only from a single record in the nasal area, was detected across the entire hairy skin of the body. These findings confirm a widely observed universal pattern of parasitism in demodecid mites, where the mammal host is inhabited by a host-specific species associated with the hairy skin region, which are accompanied by additional mite species occupying separate microhabitats. The current study also underscores the uniqueness of the beaver acarofauna and reveals previously unknown biological features within the Demodecidae, including the transfer of eggs and probably larvae.

The largest Eurasian rodent, the Eurasian beaver Castor fiber, is known for its amphibious lifestyle that allows it to adapt its environment to its needs. Due to its lifestyle and evolutionary history, the beaver is characterized by a distinct, unique parasitofauna. In this context, the occurrence of mites from the Demodecidae family in the Eurasian beaver was investigated. The topography of the Demodex castoris was analyzed: it was previously known from a single record from a single skin location of this host. The mite was found in large numbers in various locations in the hairy skin, including the head, trunk, and limbs. In addition, a new species associated with hairless skin, mainly around the mouth, was discovered and described: Demodex ovaportans sp. nov. The females of this species carry the egg on the dorsal side of the podosoma, which may be a form of care and a previously unknown reproductive strategy in Demodecidae. Our findings confirm that a host-specific demodecid mite species associated with the hairy skin of the entire body is a universal model in mammals. They also emphasize the uniqueness of the beaver parasitofauna, as evidenced by the host specificity and the different biology of the demodecids described in it.