Bioluminescent Wonders in Michigan

by Emma Kull, MNA Communications Intern

Fireflies are a well-known member of the beetle family that live all across the United States. Including the estimated 170 species in North America, there are over 2,000 species of fireflies worldwide on every continent except Antarctica. Their wondrous bioluminescence is a special sight to behold, admired by children and adults alike. Michiganders may recall summertime memories of running around their backyard with joy searching for these creatures, waiting for the next tiny glow to illuminate the night. As it turns out, that unique glow is not just a feature of the adult firefly: the firefly eggs and larvae can glow too!

Firefly adult beetle at MNA’s Clifford R. and Calla C. Burr Memorial Nature Sanctuary. Photo by Angie Adamec.

Fireflies begin their lives as small eggs, sometimes clustered together with up to 100 other eggs. These firefly eggs can be found in moist soil or vegetation during the summer where they develop for about a month. For some species of firefly, these eggs will emit a dim glow.

As the summer turns to fall, the firefly eggs transition to their next stage of life and become larvae. They live as larvae throughout the fall, feeding on insects, worms, and snails. As the winter approaches in Michigan, they survive the cold temperatures by burrowing into the ground where they stay dormant for several months. The larvae then emerge from the ground in spring. Firefly larvae, much like they did as eggs, can produce light. However, unlike firefly eggs and adults, which may or may not emit light, all species of firefly larvae glow. Hence, they are often referred to as ‘glowworms’ in this stage of their lives. The naturally occurring chemicals in firefly larvae give them a bitter taste, making them undesirable as prey. Thus, some scientists believe glowworms are bioluminescent to warn potential predators of their bad taste. The beauty of the glowworm is only magnified by the rarity of actually encountering one, as they are more difficult to stumble upon compared to the adult fireflies that dance through the night sky.

Firefly larvae emit a bioluminescent light to warn potential predators of their unsavory taste. Photo by Alexandra Karelian via Adobe Stock, @karelian – stock.adobe.com

The glowworms pupate later in the spring and emerge as adult fireflies, on average, a few weeks after pupation. Once fireflies have reached their adult stage, they only live for a few weeks to a month. Therefore, a firefly’s main goal is to reproduce within that short lifespan. As adults, some fireflies produce light and others do not. Those that do typically only illuminate for mating proposes, yet they have also been observed to do so for other reasons, like defending territory. The male firefly will fly around, flashing a specific light pattern to attract a mate. The female will then flash her own signal, indicating her interest in that male. Adult fireflies that do not produce light instead use pheromones to find mates and reproduce.

As many have never had the chance to see a firefly in a pre-adult stage, it may be surprising to discover that fireflies begin glowing so early. Those who have witnessed one are certainly lucky!