The present paper focuses on three species belonging to the family Hippoboscidae: Hippobosca equina, Lipoptena cervi and L. fortisetosa – haematophagus ectoparasites typical of cervids. In Europe, the forest flies (H. equina) are observed mainly in horses and cattle, but the primary host of this parasite is the red deer (Cervus elaphus). The host group of deer keds Lipoptena sp. include different ruminant species belonging to Cervidae (moose, red deer, sika deer, fallow deer, roe deer and maral) and Bovidae family (mouflon, european bison, cattle, sheep and goat). Furthermore, some species of carnivores (European badger, dog and red fox) can be accidental hosts. The presence of adult hippoboscid flies in the environment shows strong seasonality. One or two generations of H. equina occurs from May to October. The alate forms of univoltine Lipoptena cervi and probably multivoltine L. fortisetosa appear from August to September, and from June to September, respectively. During warm autumns, both species can be observed in late October, or even November. Hippobosca equina and Lipoptena cervi are native species, unlike the foreign L. fortisetosa. This Asian species was noted in Europe for the first time in the 1960s, and has rapidly spread in numerous countries. The most probable way of L. fortisetosa introduction to Europe was translocation via host (probably sika deer), or natural dispersion throughout Eurasia. Therefore L. fortisetosa should be treated as an alien invasive species in Poland and Europe. Interest in these three neglected dipteran species has increased after reports of their veterinary and medical importance. All these parasite species are able to attack humans. Bites of these insects are considered painful, cause skin lesions with the presence of characteristic persistent pruritic papules, and, in extreme cases, may result in an anaphylactic reaction. Hippoboscids can play a role in the transmission of bacterial pathogens, including Anaplasma and Bartonella genera, dangerous for humans and animals. Permanent and intensive attacks on humans, during the seasonal mass occurrence of these parasites, can hinder forestry work, as well as harvesting, recreation, and hunting activities in forested areas.