Can African Fat-Tailed Geckos Eat Fireflies / Lightning Bugs?

Lethal. Fireflies produce lucibufagins — defensive steroids that are acutely toxic to geckos and other insectivorous reptiles. A single firefly has killed geckos in documented cases. There is no safe amount and no antidote. This applies to all firefly species regardless of whether they appear to glow. Never feed any wild-caught insect.