There are some more legends on fireflies I know of, and two that have some relation to shadowy types:
In some Mayan legends, fireflies provide light and witness grim scenes at night, such as sacrifice. It is usually that of baby jaguars, and their light is associated with cigars and smoke.
In India, one myth says that emeralds come from fireflies in moonlight. And while they can provide protection at sea and are an antidote to some poisons, their green color ties them to jealousy, and they can also be used to call out dark spirits.