By Melissa Kaplan
Several years ago, I received an email from a reptile veterinarian inquiring about possible toxicity of fireflies. He himself had received a call from a poison control center in their quest to find out if fireflies were toxic. The poison control center had received a call from another veterinarian who was reporting two bearded dragons dead after eating fireflies.
Through the years, other lizard deaths had been reported as happening after consumption of fireflies. In all cases, the lizards were not native to North America, or not native to those parts of North America where fireflies are found.
Researchers are uncovering chemicals in fireflies that are related to their luminescence. Some of these chemicals are cardenolides, similar to digitalis. Some are like the bufadienolides found in toads. These flying beetles also contain lucibufagins, a steroidal pyrone. Luciferin, a protein, circulates through the insect's blood stream, making the entire insect toxic to a wide variety of predators.
Since that first inquiry in 1996, every year, posts appear in reptile forums either inquiring about the suitability of fireflies as food or reporting a lizard death. In the past five years, reports of toxicity and warnings started to appear in the veterinary and zoo literature.
The fireflies' glow plays a dual role in the life of these beetles. The glow advertises the males' presence to females during the annual mating dance. But the glow also warns predators of the dangers of eating the beetles. Thus, birds and other potential predators are warned off, or learn the hard way that eating a firefly isn't a mistake that they can make twice.
Many people with insectivorous herps like to increase the variety of food offerings to their animals by capturing wild insects. The problem is that we may unwittingly--and tragically--offer our animals species that are toxic to them. Contrary to popular belief, animals do not always know instinctively what is safe to eat and what is not. Once you take an animal out of its native environment, it cannot distinguish between safe or harmful plants or prey. Species that are native to one part of a country cannot be expected to instinctively know whether or not plants and prey not found in its native range are toxic or safe. Thus, a desert iguana or blue-belly swift from California are not going to know what species caught by their mid-western owner is safe or not. As far as they are concerned, anything the owner puts into their enclosure is food, and so they eat.
If you keep species not native to where you live, you need to exercise great caution when capturing wild prey for them. Animals who co-evolve over generations upon generations with the plants and prey in their native range often develop biological or anatomical countermeasures to the defense systems developed by the plants and prey they eat. That does not mean, however, that all plants and all prey within a native's ecosystem are safe to feed.
For the safety of your herps: When in doubt, check it out or leave it out.
Sources and Additional Reading
Abrams, Tom. AOL Reptile & Amphibian Forum posting. 1996.
Barten, Stephen L. Personal communication. 1996.
Exotic Deaths Linked to Fireflies ENN, 1999
Glor, R and JA Richardson. Fireflies Toxic to Bearded Dragons. Exotic DVM 2(1):6 Feb '00
Knight, Michael, Richard Glor, Scott R. Smedley, Andres Gonzalez, Kraig Adler, Thomas Eisner. Two Cases Of Firefly Toxicosis In Lizards. Chemical Ecology, in press 1999.
Segelken, Roger. Biologists alert: Poisonous fireflies are killing exotic zoo and pet lizards. Cornell Chronicle, August 1999.
Take Care of Pet Lizards! Ecotopics News.
Jackson, Melissa. Shedding Some Light On Fireflies. Chem Ecology Educational Center. August 2001.
Canadian Biodiversity. Fireflies and Lightening Bugs. McGill University.
Sprague, Terry. Fireflies. Nature and Stuff.