To many of us insects are nothing but creepy crawlies, ugly little nasties, and annoying pests. But insects are animals that play an important role in our world and there are literally millions of spieces of insect. They are a subgroup of the group called arthropods. Arthropods are creatures with segmented bodies and exoskeletons.
There are a number of characteristics that make them easily identifiable and distinguishable from other animals that you might mistake for insects if you don’t know any better. 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, the thorax is connected to the head, much like a human torso. And the abdomen is attached to the thorax, like the backside of the insect.
The next distinct characteristic of insects is that they have six jointed legs. There are three pairs of legs in all, and all of them attach 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. It is worth noting that this is typical of insects, but that a small number of insects do not have antennae. One more charcteristic is the presence of wings. 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 fairly straightforward to identify insects based on those characteristics. The trouble comes at stages of the insect’s life cycle when it may not display all of those features. For example, caterpillars do not exhibit wings or antennae, but later when they become butterflies they will. So it is important to view both adult and developing specimens.
Let’s take a look at a couple of creatures that are commonly confused with insects. Spiders are not insects, they are arachnids, as we can see by counting their legs. Spiders have eight legs, so right away we know that they can’t be 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 fixed number of legs, but have one pair of legs per body segment. And centipedes can have many body segments.
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