To many of us insects are nothing but creepy crawlies, ugly little nasties, and annoying pests. However, insects are creatures that have an important place in our world, with literally millions of spieces of insects in existence. They are a subgroup of the group called arthropods. Arthropods are creatures with segmented bodies and exoskeletons..
Insects can be told apart from other similar-looking creatures by looking at a few specific characteristics that are easily to judge. One of those characteristics is having three distinct segments of the body. Those three segments are the head, the thorax, and the abdomen. The head is self explanatory, while the thorax is connected to the head, much like a human torso. And the abdomen connects to the thorax, and looks like the backside of the creature.
The possession of six jointed legs is another thing that sets insects apart from other creatures. The three pairs of legs all connect to the thorax. If you spot a small creature with legs attached to the abdomen, then it is not an insect. Another characteristic is the presence of antennae attached to the insect's head. I should point out that while most insects do indeed have antennae, there are a few species that don't. Having wings is another characteristic of insects. There are a few types of insects that can't fly, but wings should be present at some point in their development. The last characteristic is a hard exoskeleton.
It is pretty easy to identify insects based on the above characteristics. The trouble comes at stages of the insect's life cycle when it may not display all of those features. Caterpillars, for instance, do no display wings or antennae, but when they grow into butterflies they will. So it is useful to view not only an adult specimen but also a developing one.
Let's take a look at a couple of creatures that are commonly confused with insects. It is fairly common knowledge among adults that spiders are not insects but arachnids, as we can confirm by counting their number of legs. Spiders exhibit 8 legs, so we know upon first glance that they are not insects. Slugs and snails are also not insects, as we can see if we can't their legs: they don't have any! One more example is the centipede. Centipedes are not insects but rather chilopa. They do not have a definite number of legs, but they do show one pair of legs on evert body segment. And centipedes can have many body segments.
