Scorpion Tales

By Arlen P. Walker - 24 APRIL 1987

“As you crest the hill, you see a giant scorpion ahead of you. It is facing away from you, seeming to gaze off into the distance.”

“I’ll put on my ring of invisibility and sneak past it.”

Is this possible? I thought so, until I came across the December 1984 issue of Scientific American. In that issue, Philip Brownell writes about the way sand scorpions detect their prey. Mr. Brownell’s article was not aimed at fantasy gamers, so he didn’t mention giant scorpions nor any of the other concepts which interest referees. Still, we can glean from his article some new ideas which make giant scorpions more interesting.

Scorpions use neither their visual or aural senses to detect their prey. Instead, they use the vibrations of the sand underneath them. Small sensors on their legs pick up and measure the strength of vibrations; a scorpion uses the minute differences in these vibrations picked up by each leg to locate its prey. When the scorpion has determined the distance and direction of its prey, it charges toward it with pincers extended.

Mr. Brownell gives about 30 centimeters as the maximum distance a scorpion can sense vibrations — a normal-sized scorpion, of course. A North American scorpion averages about 5 centimeters in length, which means the maximum detection distance is about six times the scorpion’s length. At a distance of about twice its length, the scorpion is almost perfect in determining both direction and distance to a victim.

Mr. Brownell’s experimental data points to a method for running encounters with giant scorpions. Up to a distance of about three times its length, the scorpion will always move to within a few feet of its target before attacking. If it makes a detection roll (1-90 on percentile dice), and if it rolls a hit against an unarmored foe (AC 10) at the end of its charge, its pincers have bumped against (but not grasped) its foe, and it may attack normally.

If its prey is farther than three times its length, the scorpion will move in the general direction of its prey up to that distance. (Generally speaking, the farther away the prey is, the more tentative the scorpion’s movement toward it will be.) In any case, if the scorpion cannot strike at its prey after it has moved, it pauses for a segment, waiting for another vibration, and reacts to it using the above guidelines. Since the scorpion uses vibrations, rather than sight or sound, to track its prey, it is immune to most camouflaging devices. Invisibility will not even confuse a scorpion, as it attacks only if its pincers have touched its prey by the end of the charge toward the prey’s expected location.

Likewise, tunneling underneath the scorpion gives no protection. The scorpion still realizes a character’s presence and can dig the character out with its large pincers. It seems obvious that a scorpion is almost impossible to surprise by any attacker who travels upon or under the ground.

The scorpion‘s detection ability should be immune to any attacks which directly affect any of the senses except touch, as that is the sense a scorpion’s vibration sensors use. The scorpion’s attack may be slightly affected by blinding attacks (- 1 or -2 to hit, depending on the success or failure, respectively, of the initial detection roll), but sonic attacks should not affect it at all.

If a scorpion is immune to all these things, then what will affect it? It should be penalized 10% on its detection roll for each leg which is missing or crippled, as the loss of sensory data from that leg impairs its ability to locate by vibration. Also, if several adjacent legs are incapacitated, the scorpion will not be able to accurately detect the direction of prey which is at a 90° angle to its missing legs. These ideas about scorpions should make for much more interesting and creative play. A scorpion is the ideal creature for demonstrating to a pesky thief or magic-user that invisibility is a vastly overrated ability.

So, the proper response to the opening situation is:

“The scorpion turns and runs directly toward you, pincers extended and stinger in the air, preparing to strike.”

And the player’s response is . . .
“RUNAWWWAAAYYYYY!!!”