Question

How do few animals glow in the dark?

Answer 1

Few animals that glow in the dark are Fireflies, glow worms, fire-flies squad and crystal jellyfish. Depending on the organism the glow is used to attract the prey, sometimes to warn the animals, escape the predator or to communicate with each other.

complete answer:
The animals that can glow have a bioluminescence. The ability to produce light by a living organism is produced by chemical reaction within the organism.
Bioluminescence is a chemical process in which an organism emits light. The lights are considered as cold lights as only a small percentage of light consists of heat. Luciferin compound which helps in producing light when it comes in contact with oxygen. Most organisms consist of their own luciferin but some absorb Bacteria that contain luciferin.
Why do animals glow?
1. Sudden glowing of light in an organism protects it from the Predator by surprising it.
2. It can also be helpful to attract prey such as in cases of angler fish.
3. It can also act as a signal to the Predator. By avoiding it thinking that it can be toxic in nature.
4. It Can attract potential males.

note:
It is estimated that about $76\%$ of ocean animals are bioluminescent which includes sea star, jellyfish. That even includes some land animals which produce light fireflies, mushrooms, beetles.