Humans have been lighting up the darkness for a long time using artificial sources. With the advent of electricity and LED bulbs, brighter nights have started to cause negative effects on a wide range of wildlife. Just recently, it was discovered that artificial lights also threaten glowing insects.
The cycles of light and dark in the natural world have been stable for so long that wildlife creatures do not have to respond to the sudden appearance of light in the middle of the night. In the animal kingdom, plenty of marine species naturally emit light for defense, hunting, and mating. This ability is limited to bioluminescent fungi and some animal species among terrestrial animals.
Environmental Impact of Light Pollution
The negative effects of artificial lighting at night (ALAN) on insects are recognized by experts and have been attributed to the decline in insect populations. Yet, the behavioral mechanism of insects remains unclear.
To address this challenge, a research team led by zoology professor Jeremy Niven from the University of Sussex conducted a study focusing on the impact of artificial light on the courtship patterns of glowing insects. They explored how artificial light at different intensities affects the behavior of male glowworms.
Niven and his colleagues placed male glowworms in a Y-shaped maze containing a fake LED female. This faux partner glows green light on one prong and white light on the other. The experiment was carried out in total darkness except for the green light, which did not interfere with the males finding their fake mate. Then the white light was turned on before returning to pitch black.
It was observed that the males became unmotivated to look for the females in the presence of white light. Male glowworms possess a head shield not used when looking for a potential partner. Upon exposure to artificial light, the males pulled their heads in and stopped attempting to search for a mate.
As explained by Niven, it is as if they covered their head inside the shield to protect themselves from the light, preferring to stop where they are. As the brightness of white light increased, multiple effects were also observed on the behavior of the males. Even if they reach the females, they take longer to do so.
On the other hand, different colors of artificial light have specific effects on fireflies. For instance, red and blue colors are more tolerable, while white and amber are much more disruptive, according to Avalon Owens from Harvard University. Female fireflies completely go dark when artificial lights are switched on. Since the males do not see any response flashes from the females, they feel dejected and prefer to flashless.
How Do Glowworms and Fireflies Glow?
Glowworms (Lampyris noctiluca) and fireflies from the Lampyridae family possess the same biochemistry. They make a kind of enzyme called beetle luciferase, which fits perfectly with a smaller molecule known as luciferin. As the enzyme and the molecule do together, it triggers a process that chemically excites the smaller molecule, giving off light as it relaxes.
Glowworms prefer grassy habitats where the males can easily see the soft green glow of the females. The females prefer to stay on the ground with their abdomens glowing for several hours as the males take flight looking for them.
Bioluminescence is a different story for fireflies. These insects use light flashes that are precisely timed to send messages about their sex and species. Male fireflies release light flashes, hoping a female will express interest by flashing her light. The male will flash again, after which the female may or may not respond.
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