The tyrus is found in some medieval encyclopedias. It is a small serpent that eats birds and their eggs. It has a deadly venom, so it was used in the preparation of a universal remedy for all poisons, because it was thought that some of the venom of a serpent should be an antidote for venom, since serpents are immune to their own venom. The preparation was called tyracca or theriaca (modern term "theriac"). It was known to the first century Greeks and throughout much of Europe into the sixteenth century. The name "tyrus" may be a corruption of the name of the preparation rather than the name of a particular serpent.

A medicine called theriaca, prepared from the flesh of the tyrus, is an antidote against all poisons.