The cantharis is found in some medieval encyclopedias. It is a green insect (worm) that glitters with gold in sunlight. They are generated by the moisture in the leaves of certain trees, where they live at the tops of branches. They are like caterpillars, but grow wings and fly in daylight; at night they gather in groups. If they are caught at night and killed with vinegar, the solution can be used to treat bladder problems.

The cantharis is killed by being immersed in vinegar, then placed on a limb that was washed with wine. This causes a burning sensation in the bladder. If the bladder is then pierced with a golden needle, an evil fluid will pour out. The wings of the insect have healing power, but the rest is poisonous.

In modern taxonomy, Cantharis is a genus of soldier beetles in the Cantharidae family.