March fly

...or Bibio pomonae (Red-thighed St Mark's fly or Heather fly)
http://en.wikipedia.org/wiki/Bibio_pomon...
http://www.gbif.org/species/1591037

Maybe it's Bibio Lanigerus.
http://galerija.foto-narava.com/displayi...
https://www.flickr.com/photos/63075200@N...

I don't believe that Bibio femoratus is found in Slovenia, or at least I can't find any sources that say it is. Bugguide is for North American arthropods, so you might want to check more local resources if they are available.

Thanks for your help! I think it is Bibio femoratus.

A march fly, Bibionidae, check Bibio species.