The diagram below shows the external anatomy of a typical Beetle.
As you can see, a typical beetle is made up much like any other insect comprising of three main parts:
Head – Thorax – Abdomen
Here are the different parts of a beetle explained.
Abdomen – this is the segmented tail end of a beetle that contains vital organs such as the heart, reproductive organs and most of the digestive system.
Thorax – this is the middle part of the beetle to which its legs and wings are attached.
Antennae – like all insects, beetles have two segmented antennae. Beetles antennae are primarily organs of smell, but may also be used to feel out a beetles environment physically. They may also 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.
Compound Eye – beetles have two faceted compound eyes which are made up of many hexagonal lenses. These eyes may display remarkable adaptability, as in the case of whirligig beetles, in which the eyes are split to allow a view both above and below the waterline. Other species also have divided eyes such as the longhorn beetles and weevils, while many beetles have eyes that are notched to some degree. A few beetle species also possess ocelli (a type of photoreceptor organ), which are small, simple eyes usually situated farther back on the head (on the vertex – the upper surface of the head).
Elytra – this is the hardened exoskeletal fore-wings that protect the hind-wings underneath.
Head – the head is at the front of the body and is the location of the brain. It also has the compound eyes, the mouth parts, the pharynx (start of the digestive system) and the two antennae attached to it.
Hind Wings – beetles have two hind wings that are used for flying and swimming. They are tucked safely under the Elytra when not in use.
Legs – beetles have six jointed legs comprising of the Femur, Tibia and Tarsus. Like many other insect orders beetles bear claws, usually one pair, on the end of the last tarsal segment of each leg. These are known as ‘Tarsal Claws’. While most beetles use their legs for walking, legs may be variously modified and adapted for other uses. Among aquatic families, the legs, most notably the last pair, are modified for swimming and often bear rows of long hairs to aid this purpose. Other beetles have fossorial legs (adapted to digging and life underground) that are widened and often spined for more effectiveness when digging. Species with such adaptations are found among the scarabs, ground beetles and clown beetles. The hind legs of some beetles, such as flea beetles and flea weevils, are enlarged and designed for jumping.
Mandibles – beetles have mouthparts similar to those of grasshoppers. 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.
Maxillary Palps – 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 palps.
Spiracles – beetles breath through ‘Spiracles’. Spiracles are openings along the body of the beetle that usually lead to respiratory systems. Air enters into them and is then taken into increasingly finer fibres. Pumping movements of the body force the air through the system. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting ‘closer muscles’ surrounding the spiracle. In order to open them, the muscle relaxes.