On a summer evening, the fireflies return

The middle of summer is a great time to see some very cool critters. Long summer evenings bring out a variety of interesting insects that we don’t see any other time of year. I was thinking about this just before sunset last night, while looking into my backyard and watching hundreds of fireflies – or lightning bugs – blinking in the warm evening air.

The firefly is a soft-bodied beetle with the remarkable ability to emit light through its body. Fireflies are found in temperate and tropical regions around the world, although many countries no longer have them. In America, they’re typically found in damp forests, wet meadows, and other protected areas with leaf litter covering the ground.

The fireflies we see this time of year are the result of adults mating and laying eggs last year. After mating, the female lays her eggs either on or just below the surface of the soil. A nice layer of dried tree leaves helps maintain the moisture needed for the eggs to survive. The eggs hatch in two to three weeks, and a small larva (tiny worm) emerges. The larva feeds until the end of summer before digging deeper into the soil to overwinter.

In spring, the larvae emerge and feed heavily on snails and slugs for a couple of weeks. The larva then pupates – a life stage in which the insect transforms into an adult – for one to two weeks and, by the dog days of summer, emerges as the adult beetle. There are more than 2,000 species of light-emitting beetles in the world, and each is slightly different in its lifecycle, light emission, and appearance. Despite their bright light, our fireflies are tiny insects – less than half an inch long.

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Fireflies produce light through a chemical process called bioluminescence. It takes place in a specialized organ where the enzyme luciferase reacts with luciferin and oxygen to create light. Oxygen is delivered through breathing tubes along the beetle’s abdomen. The result is a cold light – no heat energy is produced – making it one of the most efficient light sources in nature. The light has no infrared or ultraviolet wavelengths and is usually yellowish in color. Different species of fireflies produce green or pale red colors. 

So why do these beetles emit light? Adult fireflies use their light for mate selection. In our local species, both males and females blink their bright yellow lights on and off. The males fly around flashing, while the females remain on the ground, responding with their own blinks. This is how they find each other – and how they distinguish males from females – in the dim light of evening.

Last night while I was out, I saw a female on the ground (females are slightly larger), and a male was flying nearby. He spotted her light and landed within an inch of her. They continued blinking on and off. He walked over and circled her – perhaps figuring out the lay of the land. Once he did, he quickly mounted her so they were both facing the same direction. This brief encounter fertilizes her eggs. He then flies off, continuing to blink and search for other females. The female goes on to lay her eggs and will soon die, completing the lifecycle of the firefly.

What I find absolutely fascinating about fireflies is that there are fossilized specimens dating back 99 million years – well into the age of dinosaurs. So when I look out my window and see the flashing of fireflies, it feels like I’m looking back at ancient times – and at the same time, back at my own youth, enjoying a warm summer evening. A childhood without fireflies on a summer night is a childhood missed.

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Until next time …

Editor’s note: Stan Tekiela’s NatureSmart column appears twice a month in the Eden Prairie Local News. Tekiela is an author, naturalist and wildlife photographer who travels extensively across the United States to study and capture wildlife images. 

You can follow his work on Instagram and Facebook. He can be contacted via his website at www.naturesmart.com.