80% of all animal species on Earth are insects. Approximately 1 million species of insects have been identified, and it is believed that 6–30 million more species remain to be identified. Scientists believe that 10 quintillion (10,000,000,000,000,000,000) insects are alive at any given time.

Insects are arthropod invertebrates with an exoskeleton and 3 pairs of legs on a 3-part body. They also have a pair of antennae, and compound eyes. Insects breathe in oxygen and expel carbon dioxide through spiracles (holes in their exoskeletons), rather than breathing through their mouths.

The vast majority of insects live only a few days, some a few weeks, as adults. Most of their lives are spent as larvae and pupae, their first 2 life stages. The longest-lived insect is the termite queen, living up to 50 years. The strongest insect on Earth is a horned dung beetle. It can pull 1,141 times its body weight.

According to a new study conducted in Germany, a surprising 75% of flying insects disappeared from nature preserves over the past 25 years. Monoculture farmland, which offers insects little food, and pesticides are thought to be the causes. 90% of flowering plants, including many crops, depend on insects to survive. Many other animals rely on insects as food, including reptiles, fish, birds, amphibians, and mammals.