Jaculus, Rochester Bestiary, c.1230

The legendary jaculus is a small winged serpent which perches in trees, and when its prey approaches, throws itself down and kills its victim.

Transcription

Translation

Iaculus serpens est. volans. de quo lucanus. Iaculique
volantes. Exiliunt enim in arboribus. et dum ali-
quod animal obvium fuerit; iactant se super illud
et perimunt. Unde et iaculi dicti sunt.

A jaculus is a flying serpent, of which Lucanus says is a flying dart. For they take flight in the trees, and as long as some animal is encountered; they throw themselves upon it and perish. Whence they were called arrows.