Insect

Insects are a huge and interesting group of animals. They are part of the Insecta class and belong to the arthropod phylum. Insects have a hard outer shell called an exoskeleton. Their bodies are divided into a head, thorax, and abdomen. They have three pairs of legs, compound eyes, and a pair of antennae. There are more than a million known species of insects, which is more than half of all animal species.

Insects have special ways of living and interacting with their world. Most insects lay eggs to have babies and breathe through small openings connected to tubes that carry air to their bodies. Many insects can fly, which makes them the only invertebrates that can fly for long periods. Some insects live in water, while others live together in groups, like bees, ants, and termites. Insects are very important in nature because they help plants by spreading pollen.

Even though some insects can harm crops or spread sickness, many are helpful. Some insects eat other pests, and some, like silkworms and honey bees, give us useful things such as silk and honey. In many places, people eat insects as food. Human actions are changing insect populations, so it is important to protect these many different and valuable creatures.

Etymology

The word insect comes from the Latin word insectum, meaning "cut up." Insects look like they are divided into three parts. The idea was first used by the writer Pliny the Elder, who got it from an old Ancient Greek word meaning "cut in pieces." The English word insect was first used in 1601.

Insects and other "bugs"

Insects are often called bugs or creepy crawlies, but scientists have a special meaning for the word "bugs." True bugs are a specific group of insects that includes cicadas and shield bugs. Many other small creatures with exoskeletons, like spiders, centipedes, and millipedes, are not insects, even though they look similar. One key feature that sets insects apart is that they have a body divided into three parts: a head, a thorax, and an abdomen. They also have three pairs of legs and sometimes wings.

Insects are incredibly diverse, with scientists estimating there could be around 5.5 million different species, though only about one million have been named. Some of the most varied groups include true bugs, butterflies and moths, flies, wasps, ants, and bees, and beetles. Insects live almost everywhere — in snow, fresh water, deserts, rainforests, and even on ocean surfaces. They have adapted to many different environments, from the cold Arctic to hot deserts.

Phylogeny and evolution

Insects are a large group of animals that share a common ancestor. They belong to a group called arthropods, which also includes spiders and crustaceans. Insects are part of the Hexapoda, which means they have six legs. Their closest relatives are the Diplura, also known as bristletails.

Scientists study how insects are related to understand how they changed over time. Insects can be divided into different groups based on whether they have wings or not. Some insects, like beetles, have wings that are hard and protect their bodies. Others, like butterflies, have wings covered in tiny scales. Over time, insects have changed and adapted in many ways, becoming one of the most diverse groups of animals on Earth.

Insects have been around for a very long time. The oldest known insect fossils are from about 400 million years ago. Some insects, like the giant dragonfly Meganeura monyi, were much larger than insects today.

Morphology and physiology

Insects have a body split into three parts: the head, thorax, and abdomen. Their bodies are covered by a hard shell called an exoskeleton, made from a substance called chitin. The head has tools like antennae and eyes, while the thorax has legs and wings. The abdomen holds many important body parts.

Insects have both outer and inner body systems. Their nervous system has a brain and nerve cords. They eat through a system that runs through their body, starting at the mouth and ending at the hindgut. Insects breathe through small holes on their bodies called spiracles, linked to tubes that carry oxygen to their tissues. Their blood system is simple, with one tube that moves fluids around the body. Insects also have many senses that help them feel light, sound, smells, and more.

Reproduction and development

Insects have interesting ways of having babies and growing up. Most male insects make sperm to give to females, and they find each other using special smells.

Insects grow in different ways. Some start as eggs that hatch into small versions of adults. Others go through a big change called metamorphosis. In this process, they start as a larva, then turn into a pupa, and finally emerge as an adult.

Communication

Insects have many ways to talk to each other and stay safe. Many can make and hear sounds. For example, mosquitoes can hear up to 2 kilohertz, and some moths can hear the calls of bats to stay safe. Some insects, like fireflies, can make light to attract friends or find food.

Insects also use smells, called pheromones, to send messages. These smells can tell others where to find food, warn of danger, or attract a friend. Some insects even use vibrations on surfaces to talk to each other, especially when living in places with lots of leaves.

Social behavior

Main article: Eusociality

Social insects, like termites, ants, and many bees and wasps, live together in large groups. These groups work together very well. In these groups, only one or a few special insects, called queens, can have babies. The rest of the group works to help everyone.

These insects have special ways to talk to each other. For example, honey bees do dances to show where food is. The dance shows the direction and distance to the food. Other insects, like bumblebees, also share where to find food.

Locomotion

Insects are the only animals without a backbone that can fly. Some insects, like dragonflies, move their wings with muscles. Others flap their wings by moving their chest fast. This helps them fly quickly, sometimes faster than our brains can send messages. Insects can fly by making spinning air around their wings, or by clapping their wings together and pulling them apart to go up.

Many insects walk using all six of their legs in a special way that keeps them steady. This helps them move fast and well. Some insects, like cockroaches, can run on just two legs very fast. Other insects, like water striders, have special claws that let them walk on water without falling in. Some water insects, like water beetles, have legs like paddles to help them swim.

Ecology

Insects are very important for nature. They help keep soil healthy, spread seeds, and feed other animals. For example, termites help plants grow by changing the soil around their nests. Many beetles clean up by eating dead animals and plants. Dung beetles help by recycling waste into useful materials for other living things. Insects also help create topsoil, which is the rich layer of earth that plants need to grow.

Main article: Defense in insects

Because insects are small and delicate, they have many ways to protect themselves from predators. Some insects hide by looking like leaves or sticks. Others trick predators by looking like dangerous animals they are not. Some insects are poisonous and warn predators with bright colors. Still others can spray chemicals to scare away attackers.

Main article: Entomophily

Insects are important for helping plants reproduce through a process called pollination. When insects move from flower to flower, they carry pollen with them, which helps plants make seeds. Most flowering plants need insects to do this job. Insects often get food from flowers, such as sweet nectar, in return for their help. Flowers have evolved special colors and scents to attract their insect pollinators.

Further information: Parasitism and Parasitoid wasp

Many insects live by taking resources from other organisms. Some wasps lay their eggs inside other insects. Other insects, like fleas and mosquitoes, feed on the blood of animals, while some bugs feed on plant sap.

Relationship to humans

Main article: Human interactions with insects

Many insects are seen as pests by humans. Some, like lice and bed bugs, live on people or animals. Mosquitoes can spread diseases. Others like termites can damage wood, and locusts can destroy crops. People use different ways to control these pests.

Insects are also very helpful to humans. They help pollinate plants, including many crops. Insects like honey bees give us honey. The silkworm helps make silk. Some insects eat other pests, which helps protect crops. Scientists study insects to learn about biology and health. In some places, insects are eaten because they are nutritious.