Insects

Insects belong to a group of animals called arthropods (Arthropoda). Arthropods have jointed legs, segmented bodies and a hard outer covering called an exoskeleton.

Insects are animals that have:

• body in three parts – head, thorax and abdomen
• a pair of antennae
• six jointed legs attached to the thorax
• an exoskeleton
• mouthparts which are adapted for particular diets.

Most adult insects also have one or two pairs of wings. These features help scientists distinguish insects from other arthropods such as spiders, centipedes and crustaceans.

Insects comprise 75% of all catalogued animal species and their success is attributed to their ability to fly and adapt to many different environments. Flight allows insects to escape predators, find food and colonise new habitats. Their waterproof exoskeleton protects the body from damage. Many species also reproduce quickly, allowing populations to recover after environmental changes.

Discover some of the diversity of insects in our factsheets.

There are an estimated 5.5 million insect species. Scientists classify insects into different orders based on shared characteristics:

Insects are found on every continent, including Antarctica, where only a few species can survive the extreme conditions. Insects live in almost every habitat on Earth. They occur in forests, grasslands, deserts, wetlands, rivers, mountains and cities. Some insects spend their entire lives on land, while others live part of their lives in water. Dragonflies and damselflies, for example, develop as aquatic young before becoming flying adults.

Insects’ feeding activities recycle nutrients and support healthy ecosystems. Different species feed on plants, animals, fungi, decaying material or a combination of food sources. Many insects are herbivores, feeding on plants. Some chew leaves, while others suck sap from stems, roots or leaves. Other species act as scavengers, helping break down dead plants and animals. Find out more about corpse fauna that feed on dead bodies. Many insects are predators, others are parasites and parasitoids – living in and feeding on the host animal. Find out more about predators, parasites and parasitoids.

Insects display a wide range of behaviours that help them survive and reproduce. Some insects communicate using chemicals called pheromones. Others use sound, movement or visual signals to attract mates or warn rivals.

Some species use camouflage or have specialised mouthparts, wings, colours and body shapes suited to their environment and food source. Leaf insects and stick insects resemble leaves, twigs or branches, making them difficult to detect.

Insects play a crucial role in pollination, transferring pollen between flowers and allowing plants to reproduce. Bees are well-known pollinators, as well as butterflies, moths, beetles, flies and other insects. Pollination supports natural ecosystems and contributes to the production of many fruits, vegetables and seeds.

Over millions of years, some plants and insects have evolved close relationships that benefit both species. Ants are important in seed dispersal. They bring collected plant seeds to the nutrient rich soil of their nests, where seedlings can germinate and create new plant communities.

Most insects change form as they grow through a process called metamorphosis. Metamorphosis allows insects at different life stages to use different habitats and food sources, reducing competition within the species.

Some insects, including butterflies and moths, undergo complete metamorphosis (holometabolism). Their life cycle has four stages: egg, larva, pupa and adult. Other insects, such as dragonflies and damselflies, have an incomplete metamorphosis (hemimetabolism). Young insects, called nymphs, gradually develop adult features through a series of moults.

The earliest insects appeared more than 400 million years ago. They evolved from early arthropod ancestors and gradually diversified into many forms. With the evolution of wings insects spread into new habitats and escaped predators more effectively. Over time, insects and plants influenced each other's evolution through pollination, herbivory and other ecological interactions.

Human activities are having serious effect on insect biodiversity. Often considered pests, humans attempt to control insects using insecticides. Some species are parasitic, and may transmit diseases such as malaria. Find out more about insect bites and stings

But many insects are predators of pest insects, and some produce things we value, such as silk and honey. Insects are also a source of food in many countries.