When a peacock eats a snake, which eats insects thriving on green plants, the peacock is

The feeding interactions between organisms in an ecosystem are depicted in food chains. 

The primary consumer (herbivore), secondary consumer (carnivore), and tertiary consumer (secondary consumer) make up a simple food chain. Green plants are always at the bottom of the food pyramid since they are producers, and can synthesize food.

Green plants are producers. Insects that feed on them are primary consumers, and the snake that eats insects is a secondary consumer. Thus, the peacock is a tertiary consumer, and is at the food pyramid's pinnacle.

Primary consumers are organisms that are directly dependent on the producer (green plants). The dead organisms are broken down into smaller components by primary decomposers. Final decomposers are organisms that release nutrients back into the soil, making it fertile.