Straight from the swamps 300 million years ago, the giant spider owes its size the oxygen-rich atmosphere of the Carboniferous Period. A primitive relative of the modern spider, it lacks web and venom—but more than compensates with its enormous pincers (similar to modern-day camel spiders). Though it may look frightening, its attacks are not lethal, and it is extremely sensitive to light. This arthropod is based on rather fragmentary fossils of large spiders found in Carboniferous coal swamps. Scientists once believed the fossil “Megarachne servinei” was a 3.2-foot-wide spider, but have since reclassified it as a type of sea scorpion.