Are Fireflies Poisonous? (And 6 Other Facts About Lightning Bugs)

Written by Laura Dorr
Published: November 13, 2023
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With over 150 species of fireflies in the United States, almost everyone has seen one of these flashy insects in the warm summer months. Many people like to catch luminescent fireflies in jars to watch them light up. However, there are many poisonous and venomous species of insects in the United States which makes handling them unsafe. Are fireflies one of these dangerous species?  Here are seven facts you never knew about fireflies.

1. Fireflies Are Poisonous

common eastern firefly

On average the lifespan of a firefly is around 2 months.

©iStock.com/ErikAgar

Yes, these seemingly friendly fireflies can be poisonous. When fireflies are threatened, they can release defensive chemicals known as lucibufagins. This steroid is powerful enough to kill lizards and toads and is a great deterrent to predators such as spiders, bats, birds, and predatory insects. The chemical is not what makes fireflies glow, but is similar to the toxins (bufodienolides) that poisonous toads release to deter predators.

Not all fireflies can release lucibufagin. Fireflies fall under three groups: Photinus, Photuris, and Pyractomena. Only fireflies in the Photinus group produce the toxic chemical. It is such a good defense mechanism though that other firefly species that don’t produce lucibufagins have been known to eat Photinus fireflies. Photuris females will attract Photinus males by mimicking the flashing patterns of the poisonous genus’ females. They then eat the males to ingest the chemicals into their own bodies. The more males they eat, the more lucibufagin they have in their system, and the more unpalatable they are to predators.

Can Fireflies Hurt People and Pets?

While some species of fireflies are poisonous, they are not dangerous to humans since the lucibufagin amount is so little compared to human body mass. However, it is recommended that people do not ingest fireflies and always wash their hands after handling them.

Most pets avoid fireflies due to their taste. While cats occasionally catch one, they almost always spit it out due to its strong taste. If they do ingest it, it’s best to keep a close eye on the cat. Most cats are large enough that the lucibufagin levels aren’t high enough to make them sick. However, ingesting high levels of the toxic chemical can result in vomiting and diarrhea.

When it comes to dogs, ingesting the occasional firefly isn’t harmful. And dogs usually only make the mistake once or twice, before they learn that fireflies taste horrible!

2. What You Call Them Depends on Where You Live

Firefly blurred flying at dusk while lighting up

Fireflies live in warm and temperate climates in woodlands, parks, and meadows.

©Jeremy_Hogan/iStock via Getty Images

These glowing insects are known by many names, including fireworm, glowworm, lantern fly, firefly, and lightning bug. The last two are the most common names used in the United States. However, where you live may determine which term you use. “Firefly” is more commonly used in New England and the western part of the country, while “lightning bug” is the preferred term in the South and Midwest.

Language researchers believe that this difference may relate to weather patterns. Regions where “lightning bug” is prevalently used coincide with areas of the country that have more frequent lightning strikes. The term “firefly” is more popular in areas west of the Rocky Mountains where forest fires are more common.

3. Fireflies Aren’t Flies

Pyractomena angulata firefly

Fireflies have beetle relatives that look similar, including the soldier beetle, glowing click beetles, and the firefly-mimicking longhorn beetle.

©Judy Gallagher / Flickr – License

While “fly” is in the name (and the insects do fly), fireflies are not flies. Instead, fireflies are actually beetles in the Lampyridae family. It’s fitting that the word “lamp” is in the family name: Many of the insects in this family are luminescent.

4. They Love the South

Night firefly light

Most firefly species are nocturnal, but some are diurnal and are most active at dusk and dawn.

©anko70/Shutterstock.com

While fireflies can be found around the country, the southern states have the most firefly diversity. Florida and Georgia each have more than 50 species of fireflies in the respective states. When it comes to numbers, the Great Smoky Mountains National Park in North Carolina and Tennessee is home to enormous mating displays of synchronous fireflies (Photinus carolinus) in the late spring. Congaree National Park in South Carolina and Oak Ridge Wildlife Management Area are other popular places to see the impressive mating displays in late May and early June.

Fireflies become more scarce as you head west across the country. There are some in the Plains states, but it is incredibly rare to see them west of the Rockies. This is due to the fact that many western firefly species don’t glow as adults, or glow so faintly it is hard for the human eye to see it.

5. Medical Research Uses Fireflies

Pennsylvania firefly- official Pennsylvania state insect

The

Photuris pensylvanica

firefly is the state insect of Pennsylvania.

©iStock.com/Hlib Serbskyi

A firefly’s bioluminescence has been intriguing to researchers for a variety of medical trials. One study injected cancer cells with a chemical called luciferin produced by fireflies. After the injection, the cells lit up. When combined with a photosensitizer, the cells began to produce a topic substance that effectively killed them. This could eliminate tumors from within.  

Luciferin is also being used in imaging devices that are inserted into patients. Once the device reaches its target organ, it emits luciferin, which emits light. A portable light detector measures the intensity of the light from outside of the body, which allows doctors to identify if the organ is healthy or not.

6. They Are Predators

Pennsylvania firefly

There are around 2,000 species of fireflies worldwide.

©iStock.com/Hlib Serbskyi

These tiny harmless-looking bugs are actually predators. Firefly larvae inject insects, snails, slugs, and worms with a numbing agent to disable their prey before ingesting them. As adults, some species of fireflies eat other fireflies, while some eat nectar or pollen, or nothing at all.  

7. They Glow to Meet Partners

Fireflies

In addition to attracting mates, the distinctive flash of a firefly reminds predators to steer clear.

©Fer Gregory/Shutterstock.com

When a firefly lights up, they are trying to attract a mate. Both male and female fireflies light up, producing flashes from light-producing organs on the underside of their abdomens. Within this organ, fireflies convert chemical energy into light through a chemical reaction called bioluminescence. They communicate with different flashing patterns that differ between males and females. The pattern and brightness also vary between species. Some species flash up to nine times in a row, while others may only flash one time.

The photo featured at the top of this post is © Fer Gregory/Shutterstock.com


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About the Author

Laura Dorr is a writer at A-Z Animals where her primary focus is on wildlife. Laura has been writing about various topics for over 15 years and holds a Bachelor's Degree in English Composition from Cleveland State University. She is also a licensed wildlife rehabilitator specializing in mammal neonates. A resident of Ohio, Laura enjoys running, caring for wild animals, and spending time with her horde of cats.

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