Okay! Okay! I'm sorry I said this adventure was boring!!
Other people may feel differently, but for me, the scorpion is one creepy little crawly; certainly more so than spiders or other arachnids. Having lived in the southern United States for years, I would come across the unstriped scorpion from time to time, but the sense of alienness persists for me.
In real life, most scorpions' stings are no worse than a bee's (allergies notwithstanding). There are more venomous varieties, of course. The largest real-world scorpions clock in at about 8" long. Most are more like 1-2".
The D&D Giant Scorpion is described in Cook Expert as "the size of a small horse." Labyrinth Lord is comparable, saying 6' long. Which is middling for most of the game's "giant" creatures. Still, six feet of scorpion is ten feet too many!
While not precisely rare in adventures, these monsters are hardly common in my experience. People seem to save these for desert/mummy-type adventures, despite the fact that scorpions live in many climates. In fact, GSs are disturbingly common on the wandering monster tables. They appear on dungeon levels 6-7, and –since they are listed under the insect subtable– they can appear in six of the ten terrain types (and with two listings for insect under "jungle"). Oddly, since "insect" isn't an option there, you won't randomly encounter them in the desert.
Giant Scorpion (from Cook)
Move: 150' (50')
Att: 3 (2 claws/1 sting)
Damage: 1d10/1d10/1d4 + poison
No. App: 1d6 (1d6)
Chaotic? Really?? I would have thought that it would lack the brains for anything other than animalistic neutral, but I suspect that –and its impressive morale score– reflect its aggressive nature. ("will usually attack on sight.")
Its poison is –of course– Save or Die, but the real kicker is the fact that a successful claw attack gives the monster a +2 to hit with its stinger. Even leaving the venom aside, 1d10 per claw is pretty rough. The nasty play (DMs take note) is to attack two different PCs, one with each claw, and then follow up with the sting on whomever gets "pinched."
Their eight legs let them scurry faster than the normal character, closing quickly, and their shells are like plate mail. Round that off with 4 HD for hit points and attacks, and this thing is no pushover.
Up to six of giant scorpions per encounter is a scary time for anyone, but they are still susceptible to Sleep, so don't despair. Their saves aren't terribly impressive either. The best tactics against them is probably to keep your distance, pepper them with arrows, and hit them with spells if you can.