Spiders are not insects, nor are roly poly bugs or centipedes, or millipedes etc. Spiders are arachnids (they belong to the arachnida family) and insects belong to the Insecta family. So what are the chief differences between an insect and a spider?

1. All insects have six legs. If they don’t have six legs, they are not insects. Period. Spiders have eight legs.
2. Insects have three body parts (head, thorax and abdomen). Spiders have two body parts.
3. Most insects have wings (either one or two pairs). No spiders have wings.
4. Insects have antennae. Spiders do not.
5. Spiders have eight simple eyes. Insects have two (although they are compound eyes).

So why do so many people think that spiders are insects and where does this confusion come from? I guess because they are all mostly small and bug-like. Interesting to note is that spiders are about as closely related to insects as birds are to fish. And a roly poly (or Armadillidiidae, or pill bug) is more closely related to a lobster than to a common beetle you find it living right next to.

So the next time you hear someone say something like “spiders and other insects” or call a spider a bug or insect, please help out the scientific community and enlighten them. Or you could just write a post on your own blog with the bold title “Spiders are not insects.” Maybe the world will catch on. Or maybe not, and it’s not really that big of a deal anyway. I just wanted to write something on this blog today and thought this as good a topic as anything. Posted by admin for the best selling science toys of 2008.