This treatise involves the genus Lasiodera Gray. The species composition of Lasiodera involves Lasiodera kirbyi (Gray), Lasiodera ruficollis (Gorham), Lasiodera rufipes (Klug), and Lasiodera trifasciata (Laporte). Lectotypes are designated for L. ruficollis, L. rufipes, and L. trifasciata. Lasiodera mulleri Pic and Enoplium ornatum Klug are synonymized with L. ruficollis, and Pelonium zonatum Thomson is synonymized with L. rufipes. Morphological structures suggest that these beetles have a carnivorous life style. It is postulated that the ancestor of this monophyletic assemblage diversified in the highlands of southeastern Brazil. It is also postulated that L. kirbyi is a mimic of the velvet ant Haplomutilla spinosa (Swederus) (Mutillidae). Included in this work are an identification key to the adults of Lasiodera species, a discussion of natural history, hypotheses of evolution, two phylogenetic trees, 26 illustrations, eight SEM micrographs, four genitalic photographs, seven habitus photographs, and one distributional map.