Scorpions are land-dwelling arthropods. Like their relatives, spiders and ticks, scorpions have eight legs and two main body parts. While an individual scorpion's lifespan is relatively short by human standards—just three to eight years in the wild—the first scorpions evolved more than 400 million years ago, during a period geologists call the Silurian. This puts them among Earth's oldest surviving animals. Over millennia, the environment and competitive pressures have changed radically, but the external physical features of the scorpion have changed far less. The scorpion's survival success lies in its ability to adapt to a wide variety of habitats, adapting through behavior rather than form.

Fossil evidence suggests that scorpion ancestors lived in the water. Like crabs, marine scorpions had legs for walking along the bottom of the ocean. Gradually, as they made the transition from water to land, air-breathing lungs evolved to replace gills. Scorpions have earned the nickname "living fossils" because their basic body plan has altered little since then.

Scorpions are nocturnal and typically shelter by day. Many dig underground chambers called burrows, which moderate temperature and humidity. Scorpions also hide under rocks, in surface cracks, and in the bark of live or fallen trees. Of the 2,000 species worldwide, some live in mountain zones, while others live in deep underground caves. Some inhabit rainforests, while others call deserts home. Scorpions' adaptability to a range of living conditions and their tolerance of extreme temperatures explain their evolutionary success.

Scorpions are carnivorous, feeding mostly on insects and spiders. But a scorpion will eat almost any small animal it can capture, including lizards and rodents. Using two sets of small pincers called pedipalps, it grasps prey and transfers it to its mouth. A scorpion kills with a tail sting only occasionally. Because making venom requires energy, scorpions are selective in its use.

When food is available, scorpions can add as much as one-third of their body weight during a single meal. What's more, they efficiently transfer energy from food to their tissue. Because many scorpions do not wander more than a meter (3.28 feet) from their shelters, their metabolism and energy needs are extremely low. These characteristics can help them survive for long periods of time on a single meal.

While most scorpions are only aggressive when it comes to catching prey, they will defend their territory should other animals—or other scorpions—attempt to invade it. They also have their share of predators, including owls, snakes, frogs, and some mammals. When threatened, scorpions will use their stingers. Their venom can easily kill insects and spiders, but some predators are immune to its toxic effects. That said, 25 to 30 scorpion species have venom with toxins strong enough to kill a human.

To learn more about desert conditions and inhabitants, check out Desert Biome.

To learn more about other venomous creatures, check out Rattlesnakes and Tarantulas.

To learn more about how life evolved on Earth, check out Deep Time.

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