Lethocerus is a genus of the hemipteran family Belostomatidae, known colloquially as giant water bugs, distributed in tropical, subtropical and temperate areas of the world. The greatest diversity of species occurs in the Americas, with only a single species in Europe, two in Africa, two in Australia and three in Asia. It includes the largest true bugs with species capable of reaching a length of over . The South American L. grandis and L. maximus are the only to commonly exceed , with more typical lengths for the remaining species being between . Lethocerus sp. are distinguished from other genera in the Lethocerinae ( Benacus and Kirkaldyia) by two symmetrical furrows in the inner pad of setae on the fore femur, the external borders of parasternites II and III narrowed and nearly straight, and with the setae of the tarsomeres following the line of the tibial setae.