Mimicry is ubiquitous in nature, yet understanding its origin and evolution is complicated by the scarcity of exceptional fossils that enable behavioral inferences about extinct animals. Here we report bizarre true bugs (Hemiptera) that closely resemble beetles (Coleoptera) from mid-Cretaceous amber. The unusual fossil bugs are described as Bersta vampirica gen. et sp. nov. and Bersta coleopteromorpha gen. et sp. nov. and are placed into a new family, Berstidae fam. nov. The specialized mouthparts of berstids indicate that they were predaceous on small arthropods. Their striking beetle-like appearance implies that they were either involved in defensive mimicry or mimicked beetles to attack unsuspecting prey. The latter would represent the first case of aggressive mimicry in the invertebrate fossil record. These findings enrich our understanding of the paleoecological associations and extinct behavioral strategies of Mesozoic insects.