Fireflies belonging to the genus Photinus, which are quite common in many parts of the United States, contain chemical components called lucibufagins. These components are similar to the toxic secretions of some poisonous toads. Many species of animals can be affected by this toxic chemical, but most will avoid eating these insects.
However, we have reports that certain kinds of lizards—particularly the bearded dragon (Pogona vitticeps), an Australian native who’s become popular as a pet—have died as a result of being fed fireflies. Perhaps because they evolved in a firefly-free environment, bearded dragons don’t appear to have the innate aversion to fireflies that is present in most native animals. Therefore, it is important that reptile caretakers do not offer these insects to their pets.