This is the largest group in the animal kingdom with well over a million and a half species. The oldest known arthropods are the extinct trilobites, marine animals that flourished 550 to 450 million years ago. One type arthropod, arachnids, include spiders, mites, ticks and scorpions. All of which produce venom. Most arachnids are meat eating and partial digestion takes place outside the body when digestive enzymes are poured into prey tissue as the prey is held the animal's pincers.
Prey usually consist of other arthropods.
Scorpions are the oldest known arthropods that live on land. Fossil scorpions, very similar to present-day species, are in found in beds of rock over 400 million years old. Scorpions have six to 12 eyes depending on the species. Their breathing spores are on their abdomens. Waiting in ambush Scorpions spend the daylight hours under cover or in burrows.