• Any small creature with six jointed legs and a body divided into three parts namely head, thorax and abdomen is known as an ‘insect’.
• They have wings, two antennae and an exoskeleton. Ants, bees and flies are insects. ‘Entomology’ is the scientific study of insects, a branch of zoology.

There may be as many as 10 million species of insects including

• 3, 60,000 species of beetle
• 1, 80,000 species of butterfly and moth
• 1, 20,000 fly species
• 1, 10,000 species of bees, wasps and ants
• 82,000 true bug species (cicadas, aphids, mealy bugs, etc)
• 20,000 species of grasshoppers
• 5,000 dragonfly species
• 2,000 praying mantis species

Services to ecology and economy

• Insects play a vital role in keeping the environment in balance. They are essential for maintaining a healthy ecosystem.
• They cycle nutrients, pollinate plants, disperse seeds, maintain soil structure, improve its fertility, control population of other organisms and act as a major food source in the food chain.
• The value of nutrient cycling in the terrestrial ecosystem is assessed to be about $3 trillion.
  
• They are capable of navigating and orienting themselves using the Milky Way.
  
• They improve nutrient cycling and soil structure by burying and consuming dung.

• Many insect species are dwindling in numbers gradually globally, as well as in India. Habitat loss is a major problem. Another is increasing insecticide use.
• Some insects — less than one per cent — are major pests themselves as they destroy crops and carry diseases. Mosquitoes, tsetse flies, fleas and lice spread diseases.