How do fireflies glow? Are they charged in advance?

Produced by: Science Popularization China

Author: Chongyan Chongyu Team

Producer: China Science Expo

In the summer evening, you can often see small lights hanging in the sky among the grass and bushes in the mountain streams, as if they are competing with the stars for light, or as if couples are walking with lanterns at night. If you use a small net to cover the "small lights", you will see that they are small beetles with hard shells. Because the end of their abdomen can emit a little fluorescence, people have given them a vivid name - fireflies.

(Photo source: veer photo gallery)

Fireflies belong to the Coleoptera, Lampyridae family in the large family of insects. Fireflies are generally a few millimeters long, and the largest can be more than 17 millimeters long. Fireflies are magical and beautiful insects. They have a slender, slightly flat body with a blue-green luster, a relatively flat and wide pronotum, which often covers the head, and a pair of antennae with small teeth on the head divided into 11 segments. They have three pairs of slender, crawling legs. The male has well-developed elytra, and the hind wings are like fans, which are usually folded under the front wings and only stretched out when flying; the female has short wings or no wings. Some groups are gregarious, and it should be noted that not all species of the Lampyridae family can emit light. In the life of a firefly, it goes through four completely different insect stages: egg, larva, pupa, and adult, and is a completely metamorphosed insect.

(Photo source: veer photo gallery)

The light-emitting organ of fireflies grows in the last three segments of the abdomen of female fireflies. From the outside, it is just a layer of silver-gray transparent film, which is the fluorescent pigment. If you peel off this film and observe it under a magnifying glass, you can see thousands of light-emitting cells. Below is the reflective layer. Around the light-emitting cells are densely covered with small tracheae and dense and delicate nerve branches. The main substances in the light-emitting cells are luciferin and luciferase. When fireflies start to move, their breathing speeds up and they absorb a lot of oxygen. Oxygen enters the light-emitting cells through the small tracheae. When the luciferin interacts with the luciferase that acts as a catalyst in the cell, the luciferin will be activated, producing a biological oxidation reaction, causing the firefly's abdomen to emit a bright green light. Due to the different breathing rhythms of fireflies, a "flash signal" that is sometimes bright and sometimes dark is formed.

(Photo source: veer photo gallery)

The luciferin in fireflies is not inexhaustible, so where does the energy come from for them to glow repeatedly? It turns out that the energy comes from adenosine triphosphate (ATP), which is the energy supply substance in all living things. With this energy in fireflies, they can not only glow continuously, but also with a stronger brightness. The luminous structure alone cannot emit light, but also needs the regulation and control of the brain and nervous system. If you do an experiment and cut off the head of a firefly, the luminous mechanism will lose its function. The second and third segments of the abdomen of female insects can emit light throughout, which looks like a wide band, while the last segment only forms a dot-shaped light, which is on both sides of the body segment and can be seen from the back. The male insects can only emit light in the last segment of the abdomen, which is the same as the last segment of the abdomen of female insects, and also appears as two dots of light.

The eggs, larvae, and pupae of fireflies can all emit light. The eggs cannot emit light when they are just laid, but when they are about to hatch, two spots of light can be seen from outside the eggshell. Experiments have shown that it is caused by the movement of the larvae inside the eggshell, so it is actually the formed larvae that emit the light. The light organ can be seen at the second to last segment at the end of the larva's abdomen, but it can only emit two spots of light, which can be seen from the back. 4-5 days after pupation, there is a visible light spot on each side of the end of the pupa's abdomen, but the pupae are in a cocoon chamber made of mud and sand, so their light is not visible.

Fireflies are very efficient in emitting light, and can almost completely convert chemical energy into visible light, which is several to dozens of times more efficient than modern electric light sources. Since the light source comes from the chemical substances in the body, the light emitted by fireflies is bright but does not generate heat or magnetic fields. People call this light "cold light". Since the light of fireflies does not carry radiant heat, physicists believe that this is a very ideal light, because when things emit light, they also generate heat, such as a lit candle. Another example is that when an electric light is turned on, the light bulb also becomes hot, but people do not need the light to generate heat. It would be ideal if we could create light that does not generate heat like fireflies. Later, people simulated the principle of firefly emitting light and created a fluorescent lamp (fluorescent lamp), which basically met this requirement.

With the development of science, the application of fluorescence is becoming more and more extensive. It is used to check the bacterial content in food, to illuminate mines containing explosive gas, to indicate lights in ammunition depots, and to illuminate underwater operations.