Most people think of spiders when they hear “arachnid” but while spiders are the largest group, Arachnida contains 11 groups including spiders, scorpions, harvestman, vinegaroons, and ticks.

Most arachnid groups date back at least 400 million years! That is long before dinosaurs, even long before flowering plants, existed on Earth, making them among the first animals to have made the transition from water to land. Horseshoe crabs have recently been moved into the arachnids. They are very primitive descendants of marine arthropods.