During 2 years (1992 and 1993) the nesting biology of Auplopus militaris (Lynch-Arribalzaga 1873) was studied using trap-nests placed in a preserved natural area in the Campus of the Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, M.G., Brazil. One to 10 jug-shaped mud cells were built in each trap-nest (mode = 6). No vestibular cells were found. Cells were provisioned with one de-legged spider of the genus Corinna C.L. Koch 1841 (Corinnidae). Overall, 172 (out of 2400) trap-nests were occupied by A. militaris. Eighty-two males and 72 females emerged from 68 trap-nests. Females were significantly larger (mean thorax width = 1.558, SD = 0.169) than males (mean = 1.155, SD = 0.129) and the wasps that emerged in 1992 were significantly larger than those that emerged in 1993. Sex ratios varied between years. The estimated development time (egg to adult) ranged from 7 to 160 days, 67% of the values being between 10 and 40 days (mode = 33, mean = 39.31). Delayed emergence was observed in both years. Two species of Ichneumonidae, Photocryptus sp. (Phygadenontinae Cryptinae) (n = 29) and Colpotrichia (Colpotrichia) sp. (Metopiinae) (n = 1), and one species of Mutillidae, Ephuta pocinga (Casal 1970) (n = 9), emerged from trap-nests occupied by A. militaris. Colpotrochia (Ichneumonidae) : Parasite Photocryptus (Ichneumonidae) : Parasite Ephuta pocinga (Mutillidae) : Parasite Auplopus militaris (Pompilidae) : Host Reproduction; Life cycle and development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Population structure; Animal constructions; Land zones; Neotropical region; South America Auplopus militaris; Reproduction; Nesting biology; Life cycle; Hymenopteran parasites; Records & prevalence; Population sex ratio; Nests; Brazil; Minas Gerais, Belo Horizonte Colpotrochia; Ephuta pocinga; Photocryptus; Hymenopteran hosts; Prevalence; host life cycle; nesting biology & population sex ratio; Auplopus militaris; Brazil; Minas Gerais, Belo Horizonte none