This game is fairly challenging on a real ZX81 or a slower emulator. The keys are 'Z' to move left, '.' to jump up. The goal is not to get bit by the tarantula's (i.e. jump over them), but not to jump into the stalactites. Each time you make it across, the game moves a little faster.
Scoring is as follows: 10 points for each tarantula jumped, 100 points for completing a level. You are ranked as a 'WARRIOR' for completing the level, as a 'BLAZAER' for completing a level with 600 points, and as a 'TARANTULA CRUSHER<><>' for completing a level with a 1000 points.