Arachnids are the group of arthropods that include spiders, scorpions, ticks and mites. All arachnids have eight legs. Arachnids evolved about 500 million years ago.
Spiders are arachnids.
Their bodies are in two parts, the head and the abdomen. They do not have feelers. Most spiders have eight eyes, but some have six, four or two. Many spiders trap their food in webs. Not all spiders make webs.