A survey was conducted on the myrmecofauna of this protected zone near Barcelona (NE Spain). A total of 50 species was found. Lasius lasiodes (Emery) and Lasius cinereus Seifert are added to the fauna of Catalonia. The males of this latter species are described for the first time; their smaller size separates them from the otherwise similar males of L. grandis Forel. The head and scape are proportionately longer in L. cinereus. One sample of Lasius (Chthonolasius) was unusual since it contained two sharply distinct phenotypes differentiated by the pubescence, biometry and dregree of flattening of appendages. One form is provisionally identified as L. umbratus (Nylander); the other form is tentatively associated with Lasius rabaudy Bondroit. The presence of the invasive Argentine ant (Linepithema humile Mayr) at one of the borders of the park calls for monitoring of its eventual spread and we suggest a rehabilitation of the area presently occupied by this ant.