The muskrat (Ondatra zibethicus L.) after being introduced to Europe quickly colonized new areas. They occupied Northern, Eastern and Central Europe. One of the reasons for their successful invasion into new areas was the release of animals in numerous places and their subsequent successful self-spreading from these places. However, this semi-aquatic rodent negatively impacts the ecosystem (causes damages of watercourse embankment through burrowing, consumes crops). The species possesses a high potential for both environmental and economic impact. Nowadays, following the successful widespread of this species, abundance of its population is reduced in some countries, e. g. Lithuania and Poland. The reasons for that can be ecological factors: availability of food, diseases, parasites and carnivore predators. Moreover, humans cause significant mortality of muskrats. The rodents are extensively trapped for fur, which is of increasing economic value around the world. The paper presents a review of the muskrat introduction history into Europe and whole Eurasia, distribution of the species, the factors important for population abundance increase and reduction, on genetics as well as muskrat invasion impact on non-native ecosystems for this species.

The muskrat is hunted animal for hunting trophies, fur and financial reasons in many countries. Morphometric parameters can vary in different populations of muskrat. The aim of this work was to perform morphometric parameters analysis of skulls of muskrat in Lithuania (secondary introducents) and to compare with primary introducents (Poland and Finland) with respect to sex and weight. According to Pankakoski et al. (1987), a total of 22 measurements were taken on each skull of muskrat. The skull measurements of secondary introducents (Lithuania) females were mostly larger than those of males (p<0.05). But the muskrat skulls were longer and wider of males than of females of primary introducents (Finland and Poland). The mean values of measurements on condylobasal length (CL), braincase length (BL) and weight (BW) showed that were higher in Finnish and Polish than in Lithuanian populations of muskrat (p<0.05). These can depend on adaptive changes: habitat quality, diet and others. The strong relationship between muskrat body weight and skull length were determined in Lithuania (r=0.72, p<0.001).