Avariety of Insects
Insects belong to the phylum arthropoda, which means literally ''jointed legs''. As you may have guessed, this is one trait seen in all arthropods, including insects as well as animals like arachnids (spiders) and crustaceans (crabs).
Before delving into the characteristics of insects, it is important to clarify one point. People often refer to insects as bugs, but this is not always true. While it would be correct to say that all bugs are insects, we cannot say that all insects are bugs. True bugs belong to an order of their own, which we will discuss in a bit.
An insect body is divided into three general regions: the head, thorax, and abdomen. On the head, we find a pair of antennae and eyes. These can be either simple or compound or even both, depending on the species. For instance, a dragonfly has two compound eyes, while houseflies have both simple and compound eyes.
Also on the head we find specialized mouthparts that are used for chewing, sucking or even piercing, depending on the organism. These mouthparts are a major factor used in the classification of insects. For example, the grasshopper has a mandible that it uses for chewing grasses, while a flea has piercing and sucking mouthparts.
Chewing mouthparts of grasshopper under magnification
The thorax, or midsection, contains those features that make it possible for the insect to get around. You probably already know that insects have six legs, setting them apart from eight-legged arachnids. These three pairs of legs are attached to the thorax, as are one or two pairs of wings. Unless, of course, the subject is of the non-flying variety, such as lice and fleas.
The abdomen is the final segment of the body, and is often large and bulbous. Within the abdomen are important internal structures such as the digestive system and reproductive organs, and this is also where stingers on stinging insects are found. Insects also have a skeleton, but it is on the exterior of their body and is therefore an exoskeleton. Made of a tough material called chitin, you may have attempted to step on a beetle only to find that it is essentially protected by a coat of armor.