The glow-worm is found in some medieval encyclopedias. It is an insect that gives off light as it flies. It is not often seen before the crops are ripe or after they have been cut. They look like sparks flying in the air.

The noctiluca is described in the De proprietatibus rerum, an encyclopedia by Bartholomaeus Anglicus. Noctiluca literally mean "night shiny" (from nox, night and luceo, to shine. Bartholomaeus says it is a little beast with feet and wings, that shines in the darkness like a candle, especially from around its tail. It flees from the daylight, and infects the hand of anyone it touches. Except for it being venomous, the description of the noctiluca matches that of the glow-worm.

Blessed, then, is he who, bright in his works and the fame of his virtues, dwells among the darkness of the world, and is not seized by darkness. [Thomas of Cantimpré]

Cicindela is the genus name for the tiger beetle, and comes from the Latin meaning glow-worm. Tiger beetles have metalic colors that sometimes flash. Lampyridae is the genus name for fireflies, which emit light at night to attract mates.