Elbow leech

Elbow Leeches are large, segmented, wormlike creatures with a small mouth on one end that they use to attach to people's elbows. Elbow Leeches live in the murky waters of the Foggy Swamp. They have apparently received their name due to their uncanny ability to attach specifically to the elbow of humans and possibly other bipedal animals. They do suck blood. It is unknown if they also have a mouth on the other side of their body as well, though it appears that they are able to latch on tight enough that it will require multiple pulls on the creature before it releases its grip.

Connection
The Elbow Leech is a larger version of a regular, real-world leech. Leeches possess both front and rear suckers, though the front sucker is often very small.