In Real Life, scorpions are mostly shy, retiring creatures, preferring to stay out of trouble and only using their pincers and stinging tails to subdue prey or defend themselves (some even use them to calm down their uncooperative partners during sexual intercourse). Like spiders, they are hunters, seeking out prey by sensing vibrations through their jointed legs and hairs on their claws, using the difference in the vibrations to each leg to pinpoint the direction of the prey, much like our ears measure the difference in sound hitting one eardrum compared with the other. Scorpions also, as you may gather, have pretty difficult sex lives, with most of the males engaging in strict rituals to prevent the females from attacking or even killing them - one such ritual may involve a kind of dance where the male tries to impress the female by going toe-to-toe (or claw-to-claw, as it were) with her. Moreover, nearly all scorpions eat only small prey, rarely tackling anything much bigger than a gecko. As with spiders, only a minority of them have the venom needed to kill a human, notwithstanding allergic reactions or similar exceptions. Surprisingly, some scorpion mothers are actually pretty caring of their young, giving birth to live young and feeding and protecting them in their early childhood by carrying her brood on her back, though after they have become independent the mother will lose interest in them and even eat a few if they don't go away quickly enough.
As a general rule, the danger of a scorpion's venom is inversely proportional to the size of the scorpion and especially the size of its claws- scorpions with thick, fat tails and small, thin claws have deadlier venom to compensate, while scorpions with large claws prefer to pinch rather than sting. The sting of the Emperor Scorpion, for example, is only about as painful and venomous as your average wasp, while the Deathstalker Scorpion, a tiny creature with thin little claws, has a sting that causes excruciating pain and can (rarely) lead to death in very young or very old humans. However, proper administration of antivenom can alleviate symptoms, and should be sought out even in healthy adults.
The Emperor Scorpion is the opposite; it prefers to hunt by overpowering its prey, and it has large, muscular claws to help in that endeavor. Scorpions also have thick exoskeletons, and as they age, like all arthropods, they must shed their shell in order to grow properly. Scorpions have extremely unique mouthparts known as chelicerae that look like even smaller claws; scorpions can only digest liquid food, so their mouthparts consist of a pair of small claws on the end of small arms that can only go forward and back. The scorpion then either expels digestive juices through its mouth to the prey, or, more commonly, its venom dissolves the prey's insides, allowing the scorpion to drink them. The whole chelicerae thing is pretty unique and weird looking.
By the way, the Emperor Scorpion, probably the largest and most iconic scorpion species, is often used as the model for these Scary Scorpions, but don't fall for the Reality Is Unrealistic trap. Emperor Scorpions are good examples of the retiring type, preferring to run and hide and rarely attacking except in self-defense. Plus, they're one of the least venomous species of scorpions, as mentioned above. They also make good pets, and while perhaps not as affectionate as, say, a rabbit, there's no reason why a scorpion wouldn't make a nice companion, and even enjoy sitting in a warm hand from time to time.
Outside of the wild, scorpions are a subject of particular medical research. Scorpions are subject to a unique form of luminescence; if you shine a blacklight on a scorpion, it appears to glow a yellowish white color. Scientists don't know why they do this, but it may have something to do with temperature regulation and what rays of light scorpion exoskeleton's reflect. This could be helpful in a new, sunscreen-esque medication, if it doesn't make glowing humans. Also of note is the previously mentioned Deathstalker Scorpion. Its venom is extremely deadly, but it has a unique way of traveling through the body and can be trained to only attack certain cells. Scientists are researching the Deathstalker venom, developing ways it can help combat cancer cells, mostly by spreading a dye through them so tumors can be identified for removal.
In prehistory, scorpions were actually fairly similar to how we see them today, and the scorpions of today are of no relation to the prehistoric arthropods known as sea-scorpions, which are more closely related to horseshoe crabs and isopods. What's more, most of them weren't actually giants as we typically picture prehistoric ancestors of modern animals to be. Pulmunoscorpius, one of the largest, only grow to the size of a small-to-medium sized dog, and they only got smaller from there. Despite this, scorpions appear extensively in the fossil record with 111 prehistoric species recognized. They preyed on insects and other small animals and got preyed on by young dinosaurs and other carnivores.
Scorpions are, above everything else, survivors of the masterful sort. They outlived the dinosaurs and what killed the dinosaurs, which is no small feat. They eat anything they can wrap their claws around, and even things that hunt scorpions do so very carefully, and rarely hunt scorpions exclusively due to the dangers their venom imposes.
