Little dancing lights, the magic of summer nights

Firefly, firefly, come to me,
I’ll give you the king’s bread,
the king’s and queen’s bread,
firefly, firefly, come closer!

Thus sang the children of the last century on warm early summer nights, when the darkness, as if by magic, was illuminated by tiny flashes—an orchestra of lights over the wheat fields, near the streams, in the meadows where the grass remained tall. They would go hunting for fireflies with a handkerchief to place them under a glass; the next morning, the fireflies were gone, and in their place, they would find a few coins.
We all know fireflies, but alas, they are increasingly rare. In the space of a few years, they have disappeared from entire territories. While those of us who are older remember illuminated fields and gardens, in many places, younger generations have never even seen one.

Let’s get to know them better!

Fireflies are Coleoptera belonging to the Lampyridae family; approximately 2,000 species are known. In Italy, the most common are Luciola italica and Lampyris noctiluca.
They are characterized by their ability to emit light signals. Adults emerge in early summer; they are small, elongated, and relatively inconspicuous.

Many species exhibit marked sexual dimorphism: males are winged, while in some genera (e.g., Luciola), females are flightless. In others, such as the Lampyris genus, females are apterous, meaning they lack wings.

Adults live only 10 to 15 days and do not eat; they live solely to reproduce.
They lay luminescent eggs, which hatch into elongated, slightly flattened, and faintly bioluminescent larvae.

They live in the dark, in moist soil rich in organic matter, for two years and are formidable predators, truly ruthless killers! They feed exclusively by hunting hundreds of slugs and snails before becoming adults, using a particularly precise and effective chemical hunting technique:
Every two or three days, the firefly larva searches the soil for prey, following the slime trail left by the slugs. Once it locates its prey, which can be much larger than itself, it grabs it with its hollow, hook-shaped mandibles and, biting, injects a mixture of enzymes and toxins that paralyze the prey and liquefy its tissues from within. It then sucks up the pre-digested liquid through its mouthparts.
It’s undoubtedly a boon for vegetable gardens; wherever there are firefly larvae, the slugs disappear!

Once the larval cycle is complete, at the beginning of summer, fireflies live their final days as adults, during which they must meet to reproduce.

The upper segments of their abdomen contain photogenic organs that produce light through a chemical reaction in which luciferase, an enzyme involved in bioluminescence, acts on luciferin, an organic molecule, releasing energy in the form of visible photons and emitting a cold, yellowish-green light. This ability is the basis of the communication strategy that allows fireflies to find their mates. Typically, males fly, emitting intermittent light signals to attract females, while the latter respond by remaining still on the ground in the grass.

Females respond to males’ flashes with their own flashes, creating a form of luminous dialogue essential for mate recognition.
Between 10 p.m. and midnight in June and July, flightless females move to an area where they can be seen and reached by a male, illuminating their abdominal segments. The light signal remains active for about two hours. If a male does not arrive, the female retreats to her hiding place until the following night. This behaviour occurs for about 10 consecutive nights.

The studies conducted by Professor Floriano Papi, founder of the Pisan Ethological School, and his research team in the late 1960s helped to understand the courtship patterns of fireflies and the complex code of light communication these insects use for mating. They deciphered the system of light signals through which males and females communicate in the dark.

Unfortunately, the firefly population is rapidly declining. Habitats are shrinking and becoming fragmented, agricultural practices have changed, and the use of chemicals like metaldehyde, along with light pollution, seriously threatens their ability to survive and reproduce.
Often, there is a lack of knowledge and awareness about the impact of these factors on biodiversity. However, each of us can help. For example, we can avoid using slug killers like metaldehyde in vegetable gardens and yards, as they poison both snails and firefly larvae, as well as other predators. We can also adopt alternative, sustainable pest control methods, such as adding crushed eggshells and coffee grounds to the soil.
We could leave a corner of the vegetable garden or yard unmowed and unraked so that female fireflies can climb onto the grass to find males or lay their eggs in moist, organically rich soil.
Nighttime lights confuse males, preventing them from locating females. So, from May to July, during the courtship season, we turn off garden lights after 10 p.m.; the following year, the magical spectacle of the fireflies’ mating dance will amaze us again.

Credits

Maria Beatrice Lupi is a naturalist and an expert in training, sustainable development planning, participatory methodologies, and European planning. She is currently engaged in dissemination and education for sustainability.

Translated by Maria Antonietta Sessa