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“Krešo firefly” project – Let’s bring back the natural light of the night

Those fortunate enough to have witnessed the enchanting glow of fireflies on a warm summer evening often reminisce about the magical ambiance they create. Regrettably, such encounters are becoming increasingly rare. Why are fireflies becoming less common?

Fireflies captured at night

Fireflies captured at night. Image: Adobe Stock

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  • Fireflies are not flies, as their name suggests, but beetles. 
  • 2 000 species of fireflies belonging to different genera are found around the world, 64 in Europe. 
  • They come in various shapes and sizes and can light up the night when they appear in large numbers. 
  • Male and female fireflies often don't look alike, which adds an extra charm to their romantic dances.
  • Not just beautiful, they also help our environment by controlling pests like snails, slugs and aphids. So, they're not just pretty; they're important too!
Classification of fireflies

Fireflies, found on all continents with tropical and temperate climates, possess a remarkable feature at the tip of their abdomen — an organ that outshines LEDs in efficiency. Producing light with no heat is the most efficient bioluminescent light in the world! Fireflies employ this light for communication, locating partners, mating, and sometimes as a defense mechanism.

How do fireflies glow?

Fireflies luminesce at night thanks to an enzyme called luciferase

Fireflies luminesce at night thanks to an enzyme called luciferase. Image: Adobe Stock 

The source of the fireflies' glow is a biochemical reaction: the enzyme luciferase splits the protein luciferin into two parts (“luci-fer” means “light-bearing”). This releases energy in the form of light but without generating heat. This phenomenon is called bioluminescence.

This ability to produce light has developed independently several times over the course of evolution. Various animals like certain species of spiders, corals, jellyfish or squid can produce light through different biochemical processes.

In most of the approximately 2 000 species of fireflies, both sexes possess a light organ, while in a few species, it is a characteristic unique to one sex. Some female fireflies lack developed wings, and in certain species, females, although possessing wings, remain grounded in the grass, awaiting the arrival of their flying soulmate. Interestingly, even firefly larvae and eggs can emit light in response to external stimuli such as tapping or vibrations, possibly to deter potential predators.

Firefly feeding on a slug

Firefly feeding on a slug. Image: Adobe Stock

Firefly larvae contribute to agriculture during their lifespan of one to two years by consuming snails and larvae of other insects, thereby preventing damage to agricultural products. Adult fireflies, which live for a maximum of two months, feed on pollen and nectar, while some species do not feed at all. With fireflies in decline, it is crucial to understand and address the factors that affect these mesmerizing and beneficial creatures.

Fireflies become the streetlamps of the forests during the night

Fireflies become the streetlamps of the forests during the night. Image: Adobe Stock

In recent years, a concerning decline in the luminous presence of fireflies has been observed around the globe. This phenomenon is attributed to human influence. Fireflies typically inhabit humid and warm environments, such as forested lakes, rivers, wetlands, coastal areas, or forest paths. However, increasing urbanization and construction activities have led to a reduction in these habitats, resulting in fireflies losing their homes.

Additionally, a surge in light pollution, caused by widespread artificial lighting, is adversely affecting fireflies. It disrupts their communication patterns and hampers their ability to mate, hindering reproduction and leading to a decline in their population. As we witness the diminishing glow of fireflies, addressing these environmental challenges becomes imperative for the preservation of this enchanting species.

Croatian citizens take action

Motivated by our concern for the declining firefly population in Croatia, we, scientists from the Faculty of Agriculture at the University of Zagreb (Croatia), embarked on a mission to investigate the density of firefly populations in the country. Recognizing the logistical challenge for a small team to survey the entire nation, we turned to the citizens of Croatia for assistance. This collaborative effort gave rise to the citizen science project “Krešo krijesnica” (“Krešo firefly”). Citizen science involves the active participation of citizens in data collection and is conducted, either wholly or partially, by amateur scientists. Launched in May 2019, “Krešo krijesnica” aimed to determine the population and distribution of fireflies across Croatia.

Croatian mass media note the presence of two firefly species in the country: Ivanjska krijesnica (Lampyris noctiluca) and Mala Ivanjska krijesnica (Lamprohiza splendidula). While traditional accounts suggest that fireflies take flight at the end of June, our “Krešo krijesnica” project has revealed that they commence their flights by the end of May. This early emergence may be attributed to global warming, as the Earth's climate and temperatures are changing, potentially affecting the typical lifecycles of insects.

The “Krešo firefly” project operated by collecting via email and social networks (Facebook and Instagram) reports from citizens about the locations where they had observed fireflies. Alongside the location, contributors provided the date and the number of individuals seen, often supplementing their reports with photos and videos of the fireflies. Subsequently, we mapped the reported locations (see Picture 3), and identified the species based on the photographic evidence. The data collection process unveiled discrepancies in the classification of fireflies presented in non-scientific sources, highlighting the need for updated information.

Approximately 1 200 reports were gathered, accompanied by over 470 photographic records. Through meticulous analysis of the photos depicting the fireflies' morphology, their light organs, and the shape and color of the emitted light, 243 specimens were successfully identified. A grand total of 10 421 fireflies were reported throughout Croatia during the summer of 2019. Notably, the collection of reports revealed the presence of four firefly species in Croatia (Lampyris noctiluca, Lampyris germariensis, Lamprohiza splendidula, Luciola italica) refuting the common assumption that only two species live in the country. Furthermore, these species were found to differ even in the color of the light they emit, ranging from yellow to lime-green.

Fireflies in Switzerland

The Swiss association “Verein Glühwürmchen Projekt” engages in enhancing the habitats of fireflies, and in disseminating information about fireflies and their habitats. If you would like to support their efforts and to contribute to the preservation of these beautiful insects, you can report firefly sightings on the project's website (German, French, Italian). 

In Central Europe and also in Switzerland there are four species of fireflies:

Grosser Leuchtkäfer / Grosses Glühwürmchen – Lampyris noctiluca

Kleiner Leuchtkäfer / Kleines Glühwürmchen – Lamprohiza splendidula

Italienischer Leuchtkäfer – Luciola italica

Kurzflügel-Leuchtkäfer – Phosphaenus hemipterus

Find here a short description on species identification (German, French, Italian).

Did you know?

There may be as many myths revolving around the origin of fireflies as there are countries where they are found. 

In China, long ago, it was believed that fireflies were a product of burning grasses. There’s a Japanese legend that lightning bugs are actually the souls of the dead. Variations of the tale say that they’re the spirits of warriors who fell in battle. 

Fireflies appear in a lot of Native American folklore as well. There’s an Apache legend in which the trickster Fox steals fire from the firefly village. While the fireflies are dancing, the Fox sets a piece of bark tied to his tail on fire from the great central fire. As he escapes from the firefly village, he gives the bark to Hawk, who flies off, scattering embers around the world, which is how fire came to the people. 

Read a variation of this story here.

Open data sources

Fundamental information regarding fireflies in Croatia is catalogued within the Global Biodiversity Information Facility (GBIF). The “Krešo Firefly” citizen science initiative provides more comprehensive firefly datasets and disseminates them to the public through further open data sources. The dataset compiled in our project is accessible on the open-content platform BIOLOGER that collects biodiversity knowledge specific to Eastern Europe. Comprehensive outcomes of our project have also been published in the open-access journal Interdisciplinary Description of Complex Systems. Sharing data openly and in machine-readable formats makes it more useful for scientists and policymakers in Croatia. This collaborative effort has the potential to strengthen efforts to protect and restore firefly diversity in Croatia's ecological landscape. 

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References

Graham Harris 2019. The world's most efficient light. https://www.fireflyghg.eco/post/the-world-s-most-efficient-light Accessed 11.6.2024

*Glossary

Open Data: This is the term used to describe data that anyone may use, disseminate and reuse for any purpose.

The authors

Darija Lemić

Dr Darija Lemić

University of Zagreb
Ivana Pajac Zivkovic

Dr Ivana Pajač Živković

University of Zagreb

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