Dr. Seuss and fireflies

One firefly, two firefly, green firefly, yellow firefly. That’s what Gary Parsons said happened about a decade ago in a study of Michigan firefly species.

Parsons manages the A.J. Cook Arthropod Research Collection at Michigan State University. He said at one time, it was estimated the state held about 15 different firefly species, including flightless ones.

Scientists estimate there are 20 to 30 different firefly species in Michigan--Photo by Carolyn Sundquist

Like Dr. Seuss portrayed fish in his fictional story, “some are fast, and some are slow. Some are high, and some are low.” Scientists started to notice differences between members lumped under the same species name in Michigan.

“At some point, I would say it was about 10 years ago…we started getting these indications that these species were not just one species, that there were actually multiple species involved,” Parsons said.

Parsons estimates there could now be 20 to 30 different species based on new classifications. An easy way for Michiganders to tell without a background in entomology and firefly behavior is to glance in their backyard, he said.

“They don’t all flash with exactly the same pattern,” Parsons said.

Michiganders can determine whether multiple species live in their backyard by differences in their behavior—some fly quickly into the air as they flash their bright light, others seem to float. Flashing patterns also help the fireflies distinguish between potential mates of their own species and those that are not.

Parsons said the reaction that creates the light show of color in backyards across the state is created by enzymes when chemicals are combined.

“They can mix these chemicals and it produces light very similar to the light sticks that you break and they start glowing,” Parsons said.

The key to the reaction is luciferase, an enzyme. Luciferase speeds up a reaction between oxygen and the molecule luciferin. Luciferin releases energy in the form of light when it is combined with oxygen, producing the fireflies’ glow.

Flashing is thought to have evolved first as a mechanism to warn predators away. The glow is hypothesized to have served as a message to enemies that the larvae, which occur as glowworms, are unpalatable. Scientists believe this adaptation later served another purpose—that of attracting mates through signaling and identification

Signaling and the frequency of flashes vary. The way in which fireflies control their signaling is still unclear, but a 2008 study appearing in the Annual Review of Entomology suggested signals from the brain may trigger a series of steps that eventually allow oxygen into the cell chamber which houses luciferin, thereby allowing the bioluminescent reaction to take place and produce light.

Fireflies are often found in habitats like this one at Black River Nature Sanctuary, where grasslands merge with wooded areas-Photo by Natalie Kent-Norkowski

Parsons said there is no easy way to definitively tell fireflies apart—DNA analysis can tell, but that can take a long time after catching specimens and mailing them away.

Visual cues can show there are different species, but identifying individual species as observed is difficult. Differences vary in the shade of light color, number of flashes per second and the intensity of the light flash.

Parsons said the transitional area between woods and grassland is traditional firefly habitat, though they can also be found in open meadow. Michigan Nature Association has many sanctuaries with these habitat types.

But these beetles, which carry the “fly” name, aren’t the only ones that can “light up a room.” According to scientific literature, click beetles and railroad worms glow using the same reaction as fireflies. Many other organisms, such as some marine animals, bioluminesce through other chemical reactions.