Why does a firefly glow?

Stephen Bambara has been an extension entomologist at N.C. State University for 30 years and holds degrees in zoology and entomology. He explains how one of our favorite harbingers of summer - fireflies - achieve their telltale glow. Questions and answers have been edited.

Q: Why do fireflies glow? Is it to attract mates or ward off predators?

Fireflies (aka lightning bugs) use flashing patterns of light to attract mates. Different species have different flash patterns. There is even a predator beetle that can mimic the pattern flash of a certain female and wait to prey upon the unsuspecting male. There is also some speculation that fireflies taste bad and that the flashing acts as a warning to most other predators, rather than a place for a tasty meal.

Q: How do fireflies produce light? Do we know how they are able to turn that light on and off?

Fireflies produce a heat-free source of light through a biochemical reaction of luciferin, ATP, and the enzyme luciferase in a specialized organ. The process is called bioluminescence. It isn't precisely known how they turn the light on and off, but as soon as any of the required chemicals in the reaction are used up, the light goes out. So any one of the chemicals might be released within the organ in tiny amounts and cause flashing.

Q: Why do we only notice them this time of year, and predominantly at dusk?

These insects have evolved in their niche over millions of years. Since they are cold-blooded, they are active at warmer times of the year. It's impossible to say which came first, the blinking or the evening activity, but they definitely go together. In fact, different species of fireflies are active at different times of the evening.

Q: What is an extension entomologist?

N.C. State is a land-grant university, which has three areas: research, teaching and extension. Extension was created back in Lincoln's day with the creation of land-grant universities The idea is to extend the research to the people who needed it.

Extension specialists were created at the university level, and extension agents were placed in the counties. The extension specialists helped train and educate the agents, along with supplying educational materials, and also did applied research. So I am an extension specialist at NCSU with insects as my area of specialty.