Lethocerinae water bugs are vertebrate predators that include in their diet large prey such as fish, turtles, snakes and frogs. Although frog consumption is common among the members of the genus Lethocerus, similar reports are unknown from Europe. Here we report a predation event by an adult Lethocerus patruelis (Stål, 1854) on a subadult Balkan water frog Pelophylax kurtmuelleri (Gayda, 1940), the first description of its kind in Europe.