Firefly vs Blister Beetle
Fireflies and blister beetles are easy to mix up at a glance, but a few details separate them quickly. Here is how to tell which one you found and what, if anything, you should do about it.
Quick answer
Check for this first. A firefly has pink or red shield on the thorax with a black center spot, while a blister beetle has long, soft, cylindrical body with flexible wing covers.
Side-by-side comparison
| Firefly | Blister Beetle | |
|---|---|---|
| Group | Beetles | Beetles |
| Scientific name | Photinus pyralis | Epicauta spp. |
| Size | 10–14 mm | 8–25 mm |
| Colors | Black, Red and Yellow | Black, Gray and Orange |
| Legs | 6 legs | 6 legs |
| Wings | Yes | Yes |
| Bites or stings | No | No |
| Risk | Harmless | Can bite or sting |
| Key feature | Pink or red shield on the thorax with a black center spot | Long, soft, cylindrical body with flexible wing covers |
Key differences
- Size: Blister Beetles are larger, reaching 25 mm, while fireflies top out around 14 mm.
- Color: Fireflies are black, red and yellow; blister beetles are black, gray and orange.
- Risk: the firefly poses no real threat to people, pets or property, while the blister beetle can bite or sting, usually with mild, local effects.
- Where found: look for fireflies in lawns and grass and in woods and along trails; blister beetles turn up in gardens and on plants.
- Signature feature: Fireflies: pink or red shield on the thorax with a black center spot. Blister Beetles: long, soft, cylindrical body with flexible wing covers.
How to identify fireflies
A soft-bodied beetle that flashes a yellow-green light from its abdomen on summer evenings. Each species uses its own flash pattern to find mates.
- Pink or red shield on the thorax with a black center spot
- Pale, light-producing segments at the tip of the abdomen
- Soft, flexible wing covers edged in yellow
How to identify blister beetles
A long, soft-bodied beetle with a narrow neck that feeds on flowers and vegetable foliage. Its body contains cantharidin, a chemical that raises blisters on skin.
- Long, soft, cylindrical body with flexible wing covers
- Head wider than the narrow neck behind it
- Often black, gray or striped orange and black
Which one is more dangerous?
The blister beetle carries more risk. Handling or crushing blister beetles can cause painful skin blisters, and hay contaminated with them can poison horses.
Fireflies do not bite or sting, but they contain chemicals that are toxic to lizards and some pets if eaten. Handling or crushing blister beetles can cause painful skin blisters, and hay contaminated with them can poison horses.
Where and when you'll see each
Fireflies turn up in lawns and grass and in woods and along trails, mostly in summer. Blister Beetles turn up in gardens and on plants, mostly in summer.
Where you found the bug is itself a strong clue, since these two rarely share the same spots.
What to do if you find one
Fireflies: no control is needed. Fireflies do not bite or sting, but they contain chemicals that are toxic to lizards and some pets if eaten.
Blister Beetles: Knock beetles into soapy water with a gloved hand instead of crushing them. Read the full removal guide for more.
Biology: beetles
Beetles go through complete metamorphosis: egg, larva (grub), pupa and adult. The larval stage often does the most feeding and damage, and it can last from a few weeks to several years depending on the species. Adults protect their flight wings under hard wing covers called elytra, which is why most beetles look armored and meet in a neat line down the back.
Frequently asked questions
What is the main difference between fireflies and blister beetles?
Size: Blister Beetles are larger, reaching 25 mm, while fireflies top out around 14 mm.
Which is bigger, a firefly or a blister beetle?
Firefly: 10–14 mm. Blister Beetle: 8–25 mm.
Do fireflies or blister beetles bite?
Fireflies do not bite. Blister Beetles do not bite.
Where are they usually found?
Fireflies: in lawns and grass and in woods and along trails. Blister Beetles: in gardens and on plants.