Sources : Bedbug

Isidore of Seville [7th century CE] (Etymologies, Book 12, 5.17): The bedbug [cimex] is named for its similarity to a certain plant [cimicia] whose stench it possesses. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.18): Cymex is a worm, as Isidore says, that has it name from the similarity to a certain herb that has its stench. But it signifies the vice of the lustful, who rotted away like cattle in their dung, so that their stench troubled the heavens (that is, the spiritual ones). - [Badke translation/paraphrase]