You may have seen some of the smaller rodents, such as mice, picked up by the tail. If you do this to gerbils, you can seriously injure them. The skin on the tail of a gerbil is thin, and may actually slip off if the gerbil is picked up by the tail. If this occurs, the portion of the tail without skin will need to be amputated, or the tail will slough off.
To correctly pick up a gerbil, place your hand over the gerbil's back and encircle his body with your thumb and fingers. The gerbil may become frightened if he is not held securely. If the gerbil is used to handling, encourage the gerbil to come onto your hand, and gently encircle him with your fingers and thumb as you lift him. A final option is to coax the gerbil into a tube or cup and then place your hand(s) over the open end(s). Gerbils will usually struggle if they are held 'belly up.'