Night lights: Fireflies’ stumbling blocks in pursuit of love

How long has it been since you saw fireflies carrying small lanterns?

If you think about it seriously, it seems that the natural scenes of flashing fluorescent lights in the dark are getting farther and farther away from us. Many people have never even seen fireflies with their own eyes - indeed, there are fewer and fewer fireflies. There are so few that one can’t help but sigh: When we read ancient poems and idioms such as “The small fan flutters against the fireflies” and “The fireflies reflect the snow,” can we only imagine that scene but no longer have real and personal memories?

In fact, the dilemma faced by fireflies is the same as that of most living things - the loss of habitat has seriously affected their survival. But what you may not know is that nighttime light pollution is the second largest threat to firefly populations around the world.

Light pollution silences fireflies

In the academic world, night lighting light pollution has its own name, called ALAN (Artificial Light At Night). As the economy continues to develop and lights become brighter, ALAN has become one of the ecological problems faced by the world. It is conservatively estimated that 23% of the landmass suffers from varying degrees of nighttime lighting light pollution. Before humans used lights to light up the night sky, only celestial bodies such as the moon, stars, and luminous creatures, mainly fireflies, could embellish the darkness.

Nowadays, convenient lights have lit up our lives, but honey is like arsenic to others. Unexpectedly, the brighter and brighter lights have brought disaster to fireflies. 49 firefly researchers from different countries conducted a comprehensive assessment of firefly populations in various regions around the world and concluded that the light pollution caused by excessive nighttime lighting has put the survival situation of fireflies in danger.

▲Global nighttime light pollution map

The direct impact of nighttime light on fireflies is to reduce their activity frequency. A comparative field experiment confirmed this conclusion - in a study in the Brazilian countryside, it was found that the number of firefly appearances was significantly reduced after light exposure. Even under the weakest intensity of direct illumination (only equivalent to the light intensity of the full moon, about 0.0438 lux), the local fireflies of the genus Photinus are only half as active as when there is no light (sample 3 below). Moreover, by adjusting the light intensity and conducting parallel experiments, it was found that as the light intensity increases, the fireflies become more and more "shy", and the activity of the fireflies in the strongest light group (sample 1 below) after being affected by light is less than 10% of the original level.

Even if they are not too shy to go out because of the light, fireflies that are active under night light are still in trouble, because the light also affects their courtship behavior. After sunset, when male fireflies begin their courtship, the specific flash frequency we see is actually their romantic language of expressing love. The luminous frequency of each species is different, but in the eyes of the opposite sex of the same species, they are all unique love words.

Too bad, light pollution makes the expression of firefly love no longer accurate. After being affected by light, the male's flash parameters will change, such as frequency and intensity. At this time, in the eyes of females, these love words become strange and difficult to understand!

In addition, the light "persecutes" fireflies is not gender specific. In addition to males, females will also be affected. After a male firefly sends out a flash signal of love, if the female falls in love with him, he will respond to the love by flashing a specific frequency to indicate acceptance of courtship. Light pollution also changes the flash frequency of females.

▲ Only by communicating with accurate flash signals can fireflies reproduce successfully

The female's normal response to flashes should consist of 5 patterns, but under strong red light, the female can only emit a lonely single flash. At this time, the language of love is invalid in both directions, and the male and female can no longer understand each other's love words. This unique and beautiful courtship method has lost the effect it had for thousands of years, and the likely result is a dead end in which reproduction cannot continue.

How to reduce the impact of light pollution on fireflies?

The situation of light pollution at night is getting worse. The International Firefly Organization FIN (Fireflyers International Network) has launched an initiative calling for measures such as reducing unnecessary lights at night and transforming lighting equipment to minimize the negative impact of ALAN on fireflies.

Fireflies are rarely distributed in cities, so it stands to reason that they will not have a direct impact on their populations. But various strong light sources in cities work together to produce pollution called sky glow (one of the ALAN types). Sky glow has a wide range of effects and can even illuminate suburban areas, thereby affecting fireflies in rural environments.

In fact, simple modifications to lighting facilities can reduce the impact of sky glow, such as adding a cover to the all-round light source or appropriately lowering the position of the light source, so as to minimize the divergence of top light without affecting residents' lives.

▲Simple and effective method of urban lighting renovation

For people living in suburbs or villages, there may be an ecological environment suitable for fireflies to survive. At this time, the light source in daily life can be replaced with a sound-activated light or a timer light, which can significantly reduce the direct impact of light on fireflies. A more practical suggestion is to replace traditional light sources such as sodium lamps and mercury lamps with LED new energy lamps, because the latter are more energy-saving and durable.

In addition to the economic advantages of low energy consumption and long life, LED lights also have better ecological benefits - because the wavelengths emitted by traditional sodium and mercury lamps attract large numbers of nocturnal insects, of which moths are a typical example. In contrast, LED lights have a smaller overall impact on nocturnal insects, and the number of insects attracted by them is significantly smaller.

▲ There are fewer “moths flying into the flame” next to LED lights

Humans are also victims of light pollution

The interference of light pollution to organisms is comprehensive and extensive. In addition to fireflies, other animals (such as moths, bats, birds, and reptiles) and even plants can also be adversely affected by excessive nighttime light. Of course, humans are no exception. Long-term light pollution can cause harm to people’s sleep, emotions, endocrine and other physiological and psychological activities.

Whether we are humans or various animals and plants, as a part of nature, we have not fully adapted to this era where the night sky is as brilliant as the day. Today, as science and technology become more advanced, how to allow those animals and plants that have adapted to life in the dark for millions of years to continue to live happily is one of the issues that we should also consider as we coexist with nature.