What is the difference between an insect and a spider? They are both arthropods and we call them both bugs... but spiders and insects are two completely different species. When looking at a 'bug' and trying to figure out if it's an insect or a spider, you need to look at the number of legs, body segments, eyes, and appendages. Read on to learn more about how to identify insects and spiders. #kellysclassroomonline