In early July 1608, Gibb recorded a supposed shower of blood around Aix-la-Chapelle.
The red stains reportedly marked village walls, roadside stones and fields over several miles.
People first took the red marks for blood, but Gibb noted they were absent from places butterflies did not reach.
M. de Peiresc proposed that the drops were blood-coloured fluid exuded as large chrysalides, or butterfly pupae, transformed.
Gibb supported Peiresc’s explanation with his report that 28 Camberwell beauty chrysalides transformed in his room in one day, splattering crimson fluid on its walls and floor.