The Eurasian Eriogaster species are small Lappets. There are fourteen species listed in the LepIndex. These are tent caterpillars, building nests of sometimes more then hundred caterpillars. 

Because of their social behavior,  some precautions need to be taken to avoid diseases. If one gets sick the entire colony might die, so keep extra clean and dry. Also refresh the leaves more often then you're used to so that there is no food stress. Caterpillars of most species grow fast.