The wetland species of aculeate Hymenoptera are poorly known, even though many of them possess a potential to be used as diagnostic or flagship species in nature conservation. Here we examined 6,018 ≥1 year old galls induced by the chloropid flies Lipara spp. collected on 34 sites in the Czech Republic and Slovakia, Central Europe. We examined 1 389 nests (4 513 individuals) of nine species parasitized by one dipteran and two chrysidid parasitoids. We describe the nests of the seven most dominant species, and provide the description of larvae of four species (Pemphredon fabricii, Trypoxylon deceptorium, Hoplitis leucomelana and Hylaeus pectoralis) and two parasitoids (Trichrysis cyanea and Thyridanthrax fenestratus, both in nests of Pemphredon fabricii and Trypoxylon deceptorium), all of them but H. pectoralis preferring robust galls at very thin stalks (induced typically by Lipara lucens) over the narrow galls on thick stalks. The larvae of P. fabricii and T. deceptorium resembled strongly their sibling species (P. lethifer and T. attenuatum sensu lato, respectively). Importantly, the larvae of T. fenestratus showed different features than those suggested by its previously published descriptions. We also collected another 10,583 galls induced by Lipara spp. ≥1 year prior their collection, and allowed them to hatch. From this set of galls, we obtained 4,469 individuals of 14 nesting hymenopteran species, two cleptoparasites, three chrysidid parasitoids and one hymenopteran parasitoid. Of these species, four new nesting species have been recorded for the first time in galls induced by Lipara spp.: Chelostoma campanularum, Heriades rubicola, Pseudoanthidium lituratum and Hylaeus incongruus. We also provide first records of their nest cleptoparasites Stelis breviuscula and Stelis ornatula, and the parasitoid Holopyga fastuosa generosa. Thyridanthrax fenestratus formed strong populations in nests of Pemphredon fabricii and Trypoxylon deceptorium, which are both newly recorded hosts for T. fenestratus . The descriptions provided here allow for the first time to identify the larvae of the most widespread central European aculeate hymenopteran reed gall specialists.