Have you noticed that there are fewer and fewer fireflies around us?

Have you noticed that there are fewer and fewer fireflies around us?

When I was a child, I could encounter romantic fireflies by the small ponds in front of or behind my house, or even in my own quiet yard. But now, if you want to have a romantic encounter with fireflies, you need to go deep into the mountains and forests, to the most uninhabited areas, to see the magnificent sight of fireflies flying.

Image source: Tuchong Creative

Fireflies are becoming less and less common all over the world. There are more than 2,000 species of fireflies in the world, widely distributed in tropical and subtropical regions around the world, but coincidentally, no matter where they are, fireflies are becoming less and less common. Some fireflies have even been declared "extinct" by researchers.

The researchers investigated 15 areas in the UK where the firefly is widely distributed. They found that the populations in all areas have shown a clear downward trend over the past few years. Interestingly, this process is not a linear decline, but a period of growth before falling back to a low value. However, this is still an overall downward trend.

There are fewer and fewer fireflies, and the main culprit is, of course, humans.

There are many reasons for the decline in the firefly population. The first is the destruction and loss of firefly habitats. Fireflies usually live in lush grass, woods, and shrubs, especially around humid swamps, wetlands, lakes, streams, etc. Adult fireflies usually rest on grass or leaves during the day, and light up their tails at dusk and midnight, turning into weak but bright lights, dancing in the dim sky.

Fireflies spend most of their lives in their habitats as larvae, feeding on fallen leaves, earthworms, snails, and even shellfish near the water. They can only take a short flight after they become adults. If a suitable habitat is lost or destroyed, it will have a devastating impact on the survival of fireflies.

Unfortunately, with the expansion of urbanization, such quiet, humid places with lush trees and grass are becoming less and less. Moreover, due to the pollution of various pesticides, chemical products and insecticides used by humans, these places are no longer suitable for fireflies to survive. The water quality has deteriorated and even become toxic to fireflies, and the ecological richness has decreased, forcing fireflies to leave their habitats that are too close to humans and hide in the deeper mountains, where the ecology is relatively good, allowing fireflies to reproduce and thrive quietly.

Because fireflies are extremely sensitive to the ecological environment, they have become a special biological indicator. In areas with serious water and light pollution, fireflies will quickly die out. On the contrary, if a region can allow the firefly population to live well, or even expand year by year, then the ecological construction of this region is also very good.

The ubiquitous artificial lights are also interfering with the activities of fireflies. Light pollution at night has become the second biggest threat to the firefly population. The lighting time at night is crucial for the reproduction of the firefly population. The fluorescence of fireflies is an important prop for them to court. But under the influence of artificial lights, this firefly blind date has been disrupted.

Bright lights can mislead fireflies, making it impossible for them to find the right direction. They rush to the bright place with expectation, but there is no desired mating partner there, only a cold light. White LED lights, which are often used for street lamps and outdoor lighting, will have a serious negative impact on the reproduction of fireflies. Adult fireflies usually only live for about a week. During this week, they hardly forage for food, and only work hard to reproduce the next generation. If they fail to find their desired partner in time to complete mating, they can only die sadly in loneliness.

In addition, many human activities will affect the reproduction and survival of fireflies. For example, pesticides used in agricultural production to eliminate pests may also sound the death knell for firefly populations. For example, imidacloprid (neonicotinoid insecticide), which is commonly used in agriculture, is a widely used agricultural pesticide for broad-spectrum pest control. But it also has a strong impact on non-pest fireflies.

A study published in 2022 examined the effects of imidacloprid on Pyrocoelia analis, and found that imidacloprid is highly toxic to the larvae of Pyrocoelia analis. After exposure to imidacloprid, the larvae will show obvious tissue damage and hyperactivity. The longer the exposure to imidacloprid, the greater the toxic response of the larvae. Due to the stimulation of the nervous system by the insecticide, the larvae will also have a continuous luminous response. Extremely low doses of imidacloprid will cause irreversible physiological changes and obvious toxicity to fireflies, and this effect will persist, affecting the long-term development of the entire population.

In addition, even if fireflies do not come into direct contact with pesticides, they may be affected by pesticides entering water sources and soil. Moreover, pesticides not only affect fireflies, but also insects such as bees that often appear around fields. The impact of human activities is not limited to those limited fields, but will spread to the entire ecosystem.

Humans’ romantic fantasies about fireflies are actually one of the reasons for their extinction. In pursuit of the romantic glow of fireflies, firefly-themed tour groups have been launched all over the world, and waves of tour groups entering firefly habitats are also disrupting the normal lives of fireflies. In addition, some businesses even capture fireflies directly from the wild and transport them to cities for release. Although the moment of release is romantic, the romance is followed by the helpless death of these fireflies - they cannot return to a suitable habitat, nor can they complete their reproduction tasks, and can only welcome the decline of the population amid the cheers of humans.

Rather than pushing the firefly population into the abyss for the sake of a momentary romance, it is better to take a step back and let the fireflies be beautiful on their own. Perhaps at some point, we can relive the surprise of unexpectedly encountering a little firefly. I think this is the real romance.

The article is produced by Science Popularization China-Starry Sky Project (Creation and Cultivation). Please indicate the source when reprinting.

Author: Hydra Science Author

Reviewer: Yin Haisheng, Senior Engineer, Researcher-level, Shanghai Insect Museum, Chinese Academy of Sciences