Giant leech

Giant leeches or radioactive leeches measure about two feet long. These critters are very slow and will attack on sight.

The Hoover Dam Scum Pits are occupied by giant leeches that swim in and out of the large holes in the ground where the power generators used to be and are big enough to suck out enough blood to kill a super mutant. They also attack the giant albino rats in the Scum Pits.

Flooded sections of the sewers beneath Jericho are infested with the smaller version of these monstrosities.

Related quests
Clear out critters in Scum Pits for possible hydroponics lab - To build a hydroponics farm in the Scum Pits all kinds of nasty critters, including the leeches, must be cleared out first.

Appearances
Giant leeches were to appear in Van Buren, the canceled Fallout 3 by Black Isle Studios.