Sources : Stag-beetle

Pliny the Elder [1st century CE] (Natural History, Book 11, 34): [Beetles] are not provided with a sting, but in one large variety of them there are very long horns, with two prongs and toothed claws at the point which close together at pleasure for a bite; they are actually hung round children's necks as amulets; Nigidius calls these lucanos [Lucanos vocat hos Nigidius]. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.11; 9.19): [Worms 9.19] A stag-beetle [cervus volans, literally "flying stag"] is a worm about the size of a human thumb. It is black, has wings and flies, and its forehead is rough, with the horns of a stag. Its head, having been cut off, is said to have lived for some time, having lost its body. It bites viciously at whatever it seizes with its horns. [Worms 9.19] [Thomas mistakenly included Pliny the Elder's account of the stag-beetle in the account of the cicada.] It is also said that there is a certain kind of them that we call "flying deer" [cervus volans], which the Experimentator calls scabrones [actually the hornet, crabrones]. Under the wings, as he says, they have fine and thin wings (like a caterpillar). They fly mostly before the evening. They make a noise when flying. They have medicinal horns, long and reflexed legs. They have long, bifurcated, toothed (and shiny) horns, like forceps at the top, which, when they please, come together to bite. At night parts of their flanks and rump shine like fires, shining with the color of firefly wings; sometimes they are overshadowed by a compress [?]. Their severed heads live longer than their bodies; but the body itself lives without the head, but not so long as the head. - [Badke translation/paraphrase]