Illustration by WonderLab staff.

The Angled Candle Firefly, also known as Say’s Firefly for noted Hoosier entomologist Thomas Say, became the Indiana state insect in 2018. Although called a fire “fly” or lightning bug, like all fireflies, it is neither truly a fly nor a “bug.” (Technically a “bug” is a specific insect in the group Hemiptera with piercing mouthparts—but that’s another story for another day). Its scientific name is Pyractomena angulata and like all fireflies, it’s actually part of the beetle family.

You can spot the Angled Candle Firefly from early May through mid-July in Indiana. They are most frequently found in the wetlands and surrounding wooded areas.


All insects are distinguishable by certain characteristics. They have a head which contains sense organs, a thorax from which six legs extend, and an abdomen.


Antennae – “Feely Sensors”

The sense organs on insect heads include the eyes, mouthparts, and antennae. The antennae allow insects to respond to their environment through both tactile (touch) and olfactory (smell) receptors. 

Antennae in beetles contain 11 different segments. The first is called the scape, where the antennae connects to the head in a socket. The second segment, called the pedicel, contains muscles that enable greater range of control over the antenna as a whole. The remaining nine segments together are called the flagellum

Fireflies have filiform antennae, meaning each segment is approximately equal in size. 

Leg – “Grubby Grabbers”

Fireflies in the Pyractomena genus have six legs. Their legs tend to be about 2-4mm in length which is generally shorter than the legs of other beetles. Beetle morphology includes leg sections: femur, tibia, tarsus, and a last segment containing a claw. Beetles walk in a “tripod” fashion; a foreleg and hind leg on one side touch the ground at the same time as the middle leg on its other side. 

Wings – “Flight Flappers”

Like all beetles, fireflies have two sets of wings. The sixteen firefly species within the Pyractomena genus have top wings called elytra, which conceal hind wings. The elytra are tougher and shorter than the hind wings. They protect the insect when at rest, and provide balance during flight. The hind wings are the actual flying mechanism of the beetle and unfold when the elytra are lifted.

“Glowy Butt”

Finally, the anatomy for which fireflies are named: their glowy butts. Yes, the Angled Candle Firefly has a butt that glows. You knew that already. But how exactly do they do it – and why? 

“The light these insects produce comes from a chemical reaction called bioluminescence, in which visible light energy is released. The reaction involves a chemical burning of luciferin, the light-emitting molecule; luciferase, the enzyme that catalyzes the reaction; oxygen, which provides the burning energy, and magnesium, which facilitates the reaction. The emission of a flash is triggered by nerve impulses to the firefly’s lantern.”

Although both male and female fireflies produce light, the organs that produce light differ between sexes. In male Pyractomena, the “glowy butt” is a light organism that occupies two abdominal segments. In females, glowing occurs through only four transparent dots.

The Angled Candle Firefly glows a little differently than other fireflies (there are more than 150 different kinds in North America alone!). If you see a firefly that glows and flickers like a campfire, that’s probably an Angled Candle Firefly. Their flash is amber and pulses rapidly about 8 to 12 times per second.  Flashes happen every two to four-seconds.


Firefly populations are dwindling worldwide. Light pollution, habitat loss, and pesticide use are the most serious threats to firefly populations. Some simple ways to help from your own home are by turning off exterior lights at night, avoiding pesticides, using natural fertilizers, and letting your friends know that they can help too!

Further reading: Want to try catching fireflies? Here’s a guide to do it safely!

About the Author: Sam Ryan is a Development Intern at WonderLab. She grew up in central Missouri chasing roly-polies and running from mosquitos. She remembers many summer nights watching fireflies in her backyard and can’t wait to spot some this summer with her two-year-old daughter (if either of them can stay up late enough that is). 




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