Nests ofLindenius pygmaeus armatuswere examined in northern Poland in Kowalewo Pomorskie and Sierakowo. Adults were encountered from late May to late July. The nests were built in sandy areas and wasteland. Seven nests were observed, of which two were dug up and their structure was examined. The channel was approximately 2.5 mm in diameter and 8–10 cm in the length. The material removed during digging was placed near the nest entrance. The main burrow led to 3–5 cells. The cocoons were approximately 5–7 mm long and 2.5–3.5 mm wide. Females ofL. p. armatusprovided their nest cells with chalcid wasps averaging 14 prey items per cell. ParasitoidsMyrmosa atraand kleptoparasitesSenotainia conicawere observed entering the burrows. Both females and males ofL. p. armatuswere detected on the flowers ofAchillea millefolium,Peucedanum oreoselinum,Daucus carota, andTanacetum vulgare. The article also includes phylogenetic relationships of Western PalearcticLindeniusspecies.