EN
Instances of presumed plesiobiosis (compound nests) of Lasius umbratus (Nyl.) with Formica sanguinea Latr. and of L. umbratus with Polyergus rufescens (Latr.) are presented. At the time of nuptial flights, on the surface of nests of the dulotic species (both with enslaved Formica cinerea Mayr workers) appeared young queens of a given slave-keeper and queens of L. umbratus; local workers of F. sanguinea and (or) of F. cinerea treated them in the same way. The phenomenon was observed from 1992 to 1995 near Puławy (S-E Poland).