Photinus ignitus is the scientific name for the common North American firefly. Recent studies have shown that this firefly contains a self-defense toxin known as Lucibufagins, which is poisonous when ingested. As of yet, there have been no reports of any human victims, but reptiles and amphibians are eating the fireflies and dying within hours. Scientists suspect that the animals are becoming victims simply because they don't know any better; they are not from North America and have not learned to stay away from the deadly insect.
Source: Adopted Pets