Featured image above from firefly.org

ROCHESTER, N.Y. (WROC) — Have you ever stood outside in a field or in your yard on a warm summer evening? Then all of a sudden you see tiny bright lights popping up in your field of view in the dark… those are fireflies (or lightning bugs, more on that debate below)! It signals the unofficial beginning of summer and observing them stands as a popular activity for many this time of year.

Fireflies, also known as glowworms or lightning bugs are a part of the Lampyridae family that produce a glowing light from their abdomens, almost by magic! But it’s not magic at all. They get their famous glow by using what’s called bioluminescence.

Image courtesy: nrpa.org

How does it work?

Bioluminescence is a process that takes place from a chemical reaction that produces energy in the form of light. In order for this to happen, you need the reaction between the air (oxygen) and the organic compound luciferan, which is found in the bug’s abdomens to take place.

The enzyme luciferase acts on luciferan in the presence of magnesium ions, a chemical called adenosine triphosphate (ATP) and oxygen. The resulting light produces little to no heat, so it’s actually a very efficient way to produce light energy!

Weather and Fireflies

These insects love the warm, humid weather. This is why they are sometimes referred to as the “muggy bugs,” and why summertime is the perfect time of year where they like to come out ranging from mid May to mid June. This is when temperatures start to warm up enough for the larvae to emerge from the ground.

Weather plays a role not only when during the year you see them, but in how frequent you see the flashes of light in a given night. When overnight temperatures are warm, fireflies can thrive with an abundance of flashes of light, but on nights where temperatures drop into the 50s for example, their flashes occur a lot slower and less frequent. This happens because fireflies are cold blooded, which means they require and depend on warmth in their environment to function on a daily basis.

Did you know? During late May on the Smoky Mountains there is a synchronous firefly display that you can attend.

Depending on the weather, these insects will appear sooner depending on if we had a mild winter or not. If the winter is mild, odds are you’ll have a much larger firefly population since there’s a greater liklihood of the larvae having survived the cold winter.

Wet springs are also helpful to fireflies since the larvae feed on things like snails, slugs and pill bugs, which all come out when it rains. The more food available means the more fireflies that thrive! If the weather is too hot or dry, this can be detrimental to the larvae causing them to die before they can hatch, or cause a delay in their emergence. The flickering light of these insects aren’t just a coincidence in nature either, but they do it to attract mates and ward off predators.

Fireflies, Lightning Bugs, or both?

It’s thought that the name attached to the insect could have something to do with which phenomenon occurs most frequently in that region. Check out the regional map from author Josh Katz below:

Image courtesy: businessinsider.com

There’s a theory that exists that people who call the insects “lightning bugs” reside in an area with the most frequent lightning strikes on average. Take a look at the average U.S. total lightning density map from 2015-2019 per county below:

Image courtesy: VAISALA annual lightning report 2020

You can see that the purple and blue colors within the Midwest and Southern U.S. are where thunderstorms are most frequent, coincidentally lining up where the majority of people who say “lightning bugs.”

The data below about wildfire activity by county from 1994-2013 is a little bit older, but still shows the regional differences between who typically sees the most wildfires and who does not.

Image courtesy: dnr.wa.gov

As far as fireflies go, the region who mostly refers to them by that name see significantly greater wildfire activity. See the pattern here? It could also just be pure coincidence which name gets preferred over the other.

Firefly Fun Facts 

  • There are more than 2,000 types of firefly species
  • They are not actually “flies”. They’re beetles.
  • Not all species of fireflies glow 
  • Firefly blood contains a defensive steroid called lucibufagins, which is poisonous to predators.
  • They are not safe for pets to eat
  • Some fireflies are cannibals 
  • The color of light that you see (either yellow or green) depends on the polarity of molecules produced, and the wavelength of light. Yellow and green fall in the middle of the ultraviolet and infrared light spectrum.

So, which name do you prefer?

~Meteorologist Christine Gregory