Beetles are a very diverse group of insects. The order Coleoptera, which means "sheathed wing", has more species in it than any other taxonomic Order of animals. Forty percent of insect species are beetles. Between described and undescribed, it is estimated that the total number of species is between 5 and 8 million. Beetles are found in most habitats, other than the sea and polar areas. They feed on plants and fungi, break down animal and plant debris, eat other invertebrates, and are prey of various animals including birds and mammals. The beetle was created on the 6th day of Creation along with the other land animals and man.
The anatomy of beetles is usually uniform between the different kinds, although some organs and appendages may differ in their function and appearance within the families of the order Coleoptera. The body of a beetle is divided into three sections: the head, thorax, and the abdomen. Beetles are segmented organisms, and may have further segments in the three main segments that all beetles have. Beetles have mouthparts much like that of a grasshopper. Probably the most common part is the mandibles which look like large pincers at the front of some of the beetles. These mandibles,which move horizontally, are used to crush, grasp, or cut food or their enemies. In most beetles, there are two pairs of finger-like appendages that are found around the mouth to move food into the mouth. These finger-like appendages are called the labial palpi and maxillary palpi.
Beetles are generally characterized by their hard exoskeleton and hard forewings called elytra. The exoskeleton is made up of many plates which are called sclerites, and are separated by thin sutures. This design allows the beetle to maintain flexibility, but also gives the beetle the armoured defences it needs. The elytra tend to cover the hind part of the body,but are not used for flight. Instead they are used to protect the second pair of wings, called alae. These elytra must be raised to allow the movement of the second pair of flight wings. The flight wings of the beetle often has veins running through them, and the wings are usually folded along these veins and are stored under the cover of the elytra. Some beetles, however, do not have the ability to fly, like the ground beetle from the family Carabidae. Many of these beetles have their elytra fused together to form a shield which covers their abdomen.
Beetles have eyes that are compound, and sometimes display great adaptability, such as the whirligig beetles of the family Gyrinidae, where the eyes are split so they have a view above and below the waterline. Some other beetle species also posses eyes that are somewhat notched. A few beetle genera also have ocelli, small simple eyes, which are usually placed farther back on the head, like on the vertex. Beetle antennae are generally organs used for smell, but can also be used to feel out the beetle's environment physically. Another thing they may be used for in some families is during mating, or in some beetles for a means of defence. Antennae within the family Coleoptera vary greatly in form, but are many times similar within a given family. In some cases there are different antennal forms between males and females of the same species. Antennae can be clavate, moniliform, filiform, pectinate, geniculate, or serrate.
Beetles have multi-segmented legs that end in two to five small segments which are called tarsi, and are somewhat like feet. They have claws, usually only one pair, which are at the end of the tarsal segment of each of the legs. In some aquatic families the legs, usually the hind pair, are used for swimming and often have rows of long hairs to help this purpose. Some other beetles have legs that are often widened and spined for digging. The hind legs of some beetles, such as flea beetles in Chrysomelidae and flea weevils, are designed for jumping and are enlarged. Using a tracheal system oxygen is obtained for the beetle. Air enters tubes across the body through some openings that are called spiracles, and pumping movements force air through this system. Instead of blood they have hemolymph, and the open circulatory system is powered by a tube-like heart which is attached inside of the thorax.
Lifecycle & Reproduction
For some species, the males and females will fight until only one of each gender is left, so that only the best fit to survive will live and reproduce. The beetles that are left will pair for usually only a few hours. During this time, sperm cells from the male are transferred to the female which fertilize the egg.
All beetles go through complete metamorphosis. Beetle eggs are usually very small, and differ between species in their size, color, shape, and content. A female may produce as many as several thousand eggs to as few as several dozen to during its lifetime. The larvae of beetles are usually the feeding stage of the beetle life cycle. Larvae tend to feed ravenously once they leave their eggs. Some larvae feed on plants, while others will feed in their food sources, like wood. The larval stage length varies for different species but can last as long as several years. Beetle larvae pupate for a some time, and from the pupa emerges a fully formed, adult beetle, or the imago. Adult beetles have a very variable lifespan, ranging from weeks to years, which depends on the species of beetle.
A beetle will eat almost anything; including inorganic matter. Some beetles eat both plants and animals. Others are carnivorous and catch and consume other arthropods and small prey like earthworms and snails. Decaying matter is a main source of food for many species. Beetles and their larvae have many different tactics to avoid being eaten. One example is using camouflage to elude predators. More complex camouflage may also occur, like colored scales or colored hairs that cause the beetle to seem like bird dung. Many species can secrete a poisonous substance to defend themselves. These same species often have bright or contrasting colors to warn potential predators.
- Moonlighting: Beetles navigate by lunar polarity by Susan Milius. Science News.
- Little Beetle, Big Horns by Roberta Kwok. Science News for Kids