Beetle

Beetles are fascinating insects that make up the order Coleoptera (/koʊliːˈɒptɛrə/). They are easily recognized by their hardened front wings, called elytra, which protect their softer flying wings underneath. With approximately 400,000 known species, beetles are the largest group of insects, making up almost 40% of all described arthropods and 25% of all known animal species. Scientists believe there may be between 0.9 and 2.1 million beetle species still waiting to be discovered.

Beetles live in nearly every habitat on Earth, except for the oceans and the polar regions. They play many important roles in nature. Some beetles eat plants or fungi, while others help break down dead animals and plants. Certain beetles are pests that can harm crops, like the Colorado potato beetle, but many are beneficial, such as Coccinellidae (ladybugs or ladybirds), which eat harmful insects like aphids.

Beetles come in many shapes, sizes, and colors. Some have very short elytra, while others have softer ones. Many change dramatically from larvae to adults through a process called metamorphosis. Some beetles even glow in the dark, like fireflies, using light to attract mates. Their hard outer shell, or exoskeleton, helps protect them from danger.

Beetles have been important in human history and culture for thousands of years, from the sacred scarabs of ancient Egypt to modern art and pets. Over 300 beetle species are eaten by people, especially their larvae, such as mealworms. While some beetles can cause serious damage to crops and forests, many others are helpful friends that keep pest insects under control. The study of beetles is called coleopterology.

Etymology

The name "Coleoptera" comes from ancient Greek, where it was given by Aristotle because of their special hardened front wings called elytra. In English, the word "beetle" originates from an old word meaning "little biter," related to the idea of something that bites. There is also an old English term for beetles, "chafer," which you can see in names like cockchafer.

Distribution and diversity

Beetles are the largest group of insects, with about 400,000 known species. They make up around 40% of all described arthropods and 25% of all animal species. Scientists estimate that there may be between 0.9 and 2.1 million beetle species in total.

Beetles live in almost every habitat on Earth, from tropical forests to underground near roots. Some of the largest beetles include the goliath beetle, which can weigh as much as 100 g, and the Hercules beetle, which is the longest beetle known. The smallest beetle is the featherwing beetle, which is smaller than a grain of sand.

Evolution

Beetles have been around for a very long time. The oldest known beetle, named Coleopsis, lived about 295 million years ago in what is now Germany. Early beetles mainly ate wood and lived in places like Siberia, Europe, and the Ural mountains in Russia.

During the Jurassic period, around 210 to 145 million years ago, the number of beetle families grew quickly. Some beetles began eating plants, while others were carnivores, hunting other insects. By the Cretaceous period, beetles had spread all over the world, living in many different environments, from forests to water. Some beetles even lived on the waste of herbivorous dinosaurs. Today, beetles are one of the most diverse groups of insects on Earth.

Phylogeny

Beetles have many species, which makes it tricky to sort them into groups. The largest group is called Polyphaga, with over 300,000 species. This group includes rove beetles, scarab beetles, blister beetles, stag beetles, and true weevils (Curculionidae). Another group, Adephaga, has about 10 families of beetles that mostly hunt other insects, like ground beetles and water beetles (Dytiscidae).

Scientists have studied how beetles are related and found that all beetles come from one common ancestor. Different groups of beetles started to appear millions of years ago, with most families we see today forming during a time called the Cretaceous period.

External morphology

Beetles have a hard outer shell called an exoskeleton that helps protect them. Their front wings are hard and called elytra, which they use to cover their bodies instead of for flying. Most beetles have mouthparts with strong jaws called mandibles for eating and sometimes for defending themselves.

Beetles' bodies are divided into three main parts: the head, the thorax, and the abdomen. Their legs end in small parts called tarsi, and many beetles have special claws on the ends of their legs. Some beetles, like water beetles, have legs adapted for swimming, while others, like flea beetles, can jump using special leg parts. The wings of beetles are usually hard and used for protection, but some can still fly with their hind wings when they lift their elytra. The abdomen, or belly part, has small holes called spiracles for breathing.

Anatomy and physiology

Beetles have a digestive system suited mainly for eating plants. In some beetles that hunt other animals, digestion happens in a special part called the crop. Their nervous system includes different clusters of cells that control their movements and senses.

Beetles breathe through small holes in their bodies called spiracles. Air moves through tubes called tracheae, bringing oxygen and taking away carbon dioxide. Some beetles that live underwater carry a bubble of air to breathe. They have a simple circulatory system that moves fluids around their bodies. Certain beetles have special organs that produce smells to attract mates, and some, like fireflies, can even produce light.

Reproduction and development

Beetles are insects that go through a process called complete metamorphosis. This means they have four main stages in their life: egg, larva, pupa, and adult. The larvae, often called grubs, are the main eating stage and can look very different from the adult beetles.

Some beetles have interesting ways of finding mates. For example, fireflies use light signals to attract each other. Others may use special smells or even perform rituals before mating. The life cycle of beetles can vary a lot, but most lay eggs at some point. The larvae grow and change several times before becoming pupae, and finally, they emerge as adult beetles.

Behaviour

Beetles have interesting ways to move and communicate. Their hard front wings, called elytra, allow them to fly and also fit into tight spaces. Some beetles can fly with their elytra closed, while others have reduced elytra and mainly walk on the ground. Aquatic beetles have special ways to keep air when underwater, like holding air under their bodies or carrying air bubbles.

Beetles use different methods to talk to each other, such as releasing special chemicals called pheromones. Some beetles can even make sounds to communicate or defend themselves.

A few beetle families take care of their young. For example, some rove beetles protect their eggs and larvae from danger, while burying beetles work together to care for their offspring. Most beetles, however, do not stay with their young after laying eggs.

Beetles eat many different things depending on where they live. Some eat plants, others eat animals, and many eat decaying matter like dung or dead animals. Some beetles even have special parts to carry fungal spores.

Ecology

Beetles have many ways to protect themselves from animals that want to eat them. Some change their colors to blend in with their surroundings, like how leaf beetles are often green to look like leaves. Others look like dangerous insects, such as some longhorn beetles that mimic wasps. Many beetles produce bad-tasting or poisonous substances, and they often have bright colors to warn off predators.

Beetles also have special relationships with other living things. Some, like the ambrosia beetle, work with fungi to digest wood. The beetle makes tunnels in dead trees and grows fungus there, which provides food for both the beetle and the fungus. Other beetles help plants by moving pollen from one flower to another while they feed.

Beetles can live in very cold or very hot places by changing their bodies. Some cold-weather beetles make special proteins that stop ice from forming inside them. Desert beetles can survive very hot temperatures and even collect water from fog using special surfaces on their wings.

Relationship to humans

In ancient cultures

Main article: Scarab (artifact)

Several species of dung beetle, especially the sacred scarab, Scarabaeus sacer, were important in Ancient Egypt. The image of the beetle may have had deep meaning. The scarab was linked to Khepri, the god of the rising sun, because of how the beetle rolls its dung ball. Some of ancient Egypt's neighbors also used the scarab motif for seals. Beetles were mentioned as a symbol of the sun in writings from Plutarch. The Greek Magical Papyri described scarabs as part of spells.

Pliny the Elder wrote about beetles in his Natural History, describing the stag beetle: "Some insects are covered with a shell (elytra) to protect their wings—the beetle, for instance, has very fine wings. Some large kinds have long horns that they use to bite." The stag beetle appeared in a Greek myth recorded by Nicander and Antoninus Liberalis, where Cerambus turns into a beetle.

As pests

Many beetles feed on plants and can harm crops. The boll weevil, which feeds on cotton, entered the United States from Mexico around 1892 and became a major pest in cotton-growing areas. The bark beetle, elm leaf beetle and the Asian longhorned beetle (Anoplophora glabripennis) attack elm trees and can spread disease. Some beetles, like the Colorado potato beetle, have developed resistance to insecticides.

As beneficial resources

Beetles can help control pest populations. Lady beetles eat aphids and other pests. Ground beetles eat many insect pests and can help control weeds by eating seeds. Dung beetles help by burying animal waste, which reduces fly populations and improves soil. The Australian Dung Beetle Project brought dung beetles to Australia to help control fly populations.

As food and medicine

Beetles are eaten by people in many parts of the world, with about 344 species used as food, usually the larvae. The mealworm and the rhinoceros beetle are commonly eaten. Some cultures use beetles in folk medicine to treat various illnesses, though there is no scientific proof these treatments work.

As biodiversity indicators

Because many beetle species are sensitive to changes in their habitat, scientists use them to measure the health of an environment. Predatory beetles like tiger beetles (Cicindelidae) are good indicators because they are easy to observe and found in many habitats around the world.

In art and adornment

Beetles have been used in art and jewelry for a long time. Their hard wing covers, called elytra, are used to make beautiful objects. In parts of Mexico, beetles of the genus Zopherus are made into living brooches by attaching jewelry and chains.

In entertainment

Some people enjoy watching fights between large beetles, especially in Chiang Mai, Thailand, where male rhinoceros beetles are trained to fight. In South Korea, a type of beetle is used in a game similar to roulette. Beetles have also been used as musical instruments, such as the "hugu" weevil in Papua New Guinea.

As pets

Some people keep beetles as pets. In Japan, keeping horned rhinoceros beetles and stag beetles is very popular, especially among children.

As things to collect

Collecting beetles was very popular during the Victorian era. Naturalists would travel far to find new species.

As inspiration for technologies

Further information: Biomimetics

Scientists study beetles to create new technologies. For example, the spray made by the bombardier beetle has inspired a new type of fine mist spray. The way the Namib desert beetle collects water has led to the design of a self-filling water bottle. Some beetles have even been used in experiments to control them remotely, which could help with surveillance.

In conservation

Because beetles are such a large part of the world's animals, protecting them is important. Some species are in danger because they live in specific habitats that are disappearing. Conservationists work to raise awareness about beetles, using popular species like the stag beetle and tiger beetles to interest people. In places like Japan and South Africa, beloved beetles help bring more people to learn about nature and animals.