Stalactites hang from the ceiling, stalagmites rise from the floor of a cave.

 Mnemonic:
The 'mites go up and the 'tites come down. When one has ants in one's pants, the mites go up and the tights come down. (Note: In a strict scientific sense, a mite is not an ant, although "mite" in common speech can refer to any small creature.)

 Mnemonic:
Stalactites hang tight, hang down like tights on a line; stalagmites might bite (if you sit on them), might reach the roof.

 Mnemonic:
Tights hang from the Ceiling, and Mites crawling around on the Ground

 Mnemonic:
You need might to do push-ups (from the floor). You must hold tight doing chin-ups (off the ceiling).

 Mnemonic:
Stalactites are on the ceiling. Stalagmites are on the ground.

 Mnemonic:
Stalactites cling tight to the ceiling; stalagmites might reach the ceiling.