Anatomy Of Beetle
The general anatomy of beetles is quite uniform, though specific organs and appendages may vary greatly in appearance and function between the many families in the order. Beetle bodies are divided into three sections: the head, the thorax and the abdomen. Like all insects, beetles are segmented organisms, and all three of the major sections of the body may themselves be composed of several further segments, although these are not always readily discernable.
Beetles are generally characterised by a particularly hard exoskeleton and hard forewings (elytra). The beetle's exoskeleton is made up of numerous plates called sclerites, separated by thin sutures. This design creates the armoured defences of the beetle while maintaining flexibility. The elytra are not used for flight, but tend to cover the hind part of the body and protect the second pair of wings (alae). Elytra must generally be raised in order to move the hind flight wings.
A beetle's flight wings are crossed with veins and, after landing, are folded, often along these veins, and stored below the elytra. In some cases the ability to fly has been lost, most notably in the ground beetles (family Carabidae) and the true weevils(family Curculionidae), but also in some desert and cave-dwelling species of other families. Many of these species have the two elytra fused together, forming a solid shield over the abdomen. In a few families both the ability to fly and the elytra have been lost, with the best known example being the glowworms of the family Phengodidae, in which the females are larviform throughout their lives.
Beetles have mouthparts similar to those of grasshoppers. Of these parts, the most commonly known are likely 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. Two pairs of finger-like appendages are found around the mouth in most beetles, serving to move food into the mouth. These are the maxillary and labial palpi.
The eyes are compound, and may display some remarkable adaptability, as in the case of whirligig beetles (family Gyrinidae), in which the eyes are split to allow a view both above and below the waterline. Other species also have divided eyes (some Cerambycidae and Curculionidae), while many beetles have eyes that are notched to some degree. A few beetle genera also possess ocelli, which are small, simple eyes usually situated farther back on the head (on the vertex).
Beetle antennae are primarily organs of smell, but may also be used to physically feel out a beetle's environment. Further, they may be used in some families during mating, or among a few beetles for defence. Antennae vary greatly in form within the Coleoptera, but are often similar within any given family. In some cases males and females of the same species will have different antennal forms. Antennae may be filiform, clavate, flabellate or genticulate.
The legs, which are multi-segmented, end in two to five small segments called tarsi, which are vaguely comparable to feet. Like many other insect orders beetles bear claws, usually one pair, on the end of the last tarsal segment of each leg. While most beetles use their legs for walking, legs may be variously modified and adapted for other uses. Among aquatic families (Dytiscidae, Haliplidae, many Hydrophilidae, and others) the legs, most notably the hind pair, are modified for swimming and often bear rows of long hairs to aid this purpose.
Other beetles have fossorial legs that are widened and often spined for digging. Species with such adaptations are found among the scarabs, ground beetles, and clown beetles (family Histeridae). The hind legs of some beetles, such as flea beetles (within Chrysomelidae) and flea weevils (within Curculionidae), are enlarged and designed for jumping.
Oxygen is obtained via a tracheal system. Air enters a series of tubes along the body through openings called spiracles, and is then taken into increasingly finer fibres. Pumping movements of the body force the air through the system.
Beetles have hemolymph instead of blood, and the open circulatory system of the beetle is powered by a tube-like heart attached to the top inside of the thorax.