Beetles contain more species than any other, constituting almost 25% of all known life-forms. About 40% of all described insect species are beetles (about 400,000 species), and new species are discovered frequently. Some estimates put the total number of species, as high as 100 million, but 1 million is a more accepted figure.
The diversity of beetles is very wide-ranging. They are found in almost all types of habitats, but are not known to occur in the sea or in the polar regions. They interact with their ecosystems in several ways. They often feed on fungi, break down animal and plant debris, and eat other invertebrates. Some species are prey of various vertebrates including birds and mammals. Certain species are agricultural pests, such as the Colorado potato beetle the boll weevil, the red flour beetle, and the mungbean or cowpea beetle while other species of beetles are important controls of agricultural pests. For example, ladybugs consume aphids, scale insects, thrips, and other plant-sucking insects that damage crops.
Beetles are generally characterized by a particularly hard exoskeleton and hard forewings. The beetle's exoskeleton is made up of numerous plates separated by thin sutures. This design creates the armored defenses of the beetle while maintaining flexibility. The general anatomy of a beetle is quite uniform, although specific organs and appendages may vary greatly. Like all insects, beetles' bodies are divided into three sections: the head, the thorax, and the abdomen.
Beetles' antennae are primarily organs of smell, but may also be used to feel out a beetle's environment physically. They may also be used in some families during mating, or among a few beetles for defence.
Beetles have mouthparts similar to those of grasshoppers. Of these parts, the most commonly known are probably the mandibles, which appear as large pincers on the front of some beetles. The mandibles are a pair of hard, often tooth-like structures that move horizontally to grasp, crush, or cut food or enemies
A single female may lay from several dozen to several thousand eggs during her lifetime. Eggs are usually laid according to the food the larva will feed on upon hatching.
The larva is usually the principal feeding stage of the beetle life cycle. Larvae tend to feed voraciously once they emerge from their eggs. The larvae of many beetle families are predatory like the adults (ground beetles, ladybugs). The larval period varies between species but can be as long as several years.
Beetles have a variety of ways to communicate. Some of which include a sophisticated chemical language through the use of pheromones. They can emit both an aggregative pheromone and an anti-aggregative pheramone. The aggregative pheromone attracts other beetles, and the anti-aggregative pheromone neutralizes the aggregative pheromone. This helps to avoid the harmful effects of having too many beetles competing for resources.
Besides being abundant and varied, beetles are able to exploit the wide diversity of food sources available in their many habitats. Some are omnivores, eating both plants and animals. Other beetles are highly specialized in their diet. Decaying organic matter is a primary diet for many species.
Beetles and their larvae have a variety of strategies to avoid being attacked by predators. These include camouflage, mimicry, toxicity, and active defense.
Another defense that often uses color or shape to deceive potential enemies is mimicry. A number of beetles bear a striking resemblance to wasps, which helps them avoid predation even though the beetles are in fact harmless. Many beetle species, including ladybugs, and can secrete distasteful or toxic substances to make them unpalatable or even poisonous.
Beetle-pollinated flowers are usually large, greenish or off-white in color and heavily scented. Scents may be spicy, fruity, or similar to decaying organic material. Most beetle-pollinated flowers are flattened or dish shaped, with pollen easily accessible, although they may include traps to keep the beetle longer. The plant's ovaries are usually well protected from the biting mouthparts of their pollinators.[
Situations in which a species has developed immunity to pesticides, as in the case of the Colorado potato beetle, which is a notorious pest of potato plants. Crops are destroyed and the beetle can only be treated by employing expensive pesticides, many of which it has begun to develop resistance to.
Beetles are not only pests, but can also be beneficial, usually by controlling the populations of pests. One of the best, and widely known, examples are the Ladybugs or ladybirds. Both the larvae and adults are found feeding on aphid colonies. Other ladybugs feed on scale insects and mealybugs. If normal food sources are scarce, they may feed on other things, such as small caterpillars, young plant bugs, honeydew and nectar.
Some beetles help in a professional setting, doing things that people can't; such as those of the family Dermestidae are often used in taxidermy and preparation of scientific specimens to clean bones of remaining soft tissue. The beetle larvae to clean skulls because they do a thorough job of cleaning, and the beetle larvae do not leave the tool marks that taxidermists tools do. Another benefit is that with no traces of meat remaining, and will not develop the unpleasant dead odor. Using the beetle larvae means that all cartilage is removed along with the flesh, leaving the bones spotless.
Insects are used as human food in 80% of the world's nations. Beetles are the most widely eaten insects. 344 species are known to be used as food. They are usually eaten in the larval stage. The mealworm is the most eaten beetle species. The larvae of the darkling beetle and the rhinoceros beetle are also commonly eaten.