Felipe Gil-T. is right, it is the caterpillar of Orgyia antiqua.

@Rudolf RItt and @Felipe Gil-T.

This caterpillar is similar to Orgyia thyellina and O. antiqua.

I am a little bit confused, about the correct identification of the larvae.

Thanks all of you for concernig this intriguing me question. Though O. antiqua seems to be most common in Europe, I'd met it first time and was astonished by its beauty. From Buszko, Nowacki 2010 distributional check list it results that it is a bit rarer in Silesian Voivodeship, than in the surrounding ones.

https://www.lepidoptera.eu/show.php?ID=252

Dear All,

Felipe is right. It is a common but not frequent European species. I used to find it on my pear tree. It is a bit similar to a centurio’s helmet decoration. 

I think it is Orgyia antiqua.

Please see the following link:

http://mothphotographersgroup.msstate.edu/species.php?hodges=8308

Its behaviour was also very interesting. She (in Polish a caterpillar is of feminine gender) was really fast when finally decided to run away.

It may be Orgyia.https://warehouse1.indicia.org.uk/upload/Vapourer%20Moth,%20(Orgyia%20antiqua)%20Caterpillar%20Near%20Granitethorpe%20Quarry%20Sapcote%20SP%204960%209360%20(taken%2028.6.2009),,_caterpillar.2009),,.JPG

And what species of butterfly or moth may be this caterpillar, I'd met last month in Bieszczady Mountains, Poland?

The caterpillar of the last photo is of Euthrix potatoria (Lasiocampidae).