It is used to make a lesser antidote. And is a good fishing bait!

Use this when fishing for great drops!

On mobile leeches are one of the rarest creatures in game in fact of 3 years of playing this game I only had 2 encounters with them and I go into the swamp very often.

Death worms are also able to drop blood

If you want to attack a leech first get a araneo with a saddle ride the araneo so it doesn’t stick on you

If you kill big corrupted dinos like T Rexes or Spinos they give you leech blood for some reason.

You cannot extend leech blood spoil time by any means, except on a fishing pole, which is lame.

Be prepared to use immediately it for fishing or whatever and just craft antidotes with the rest. Antidotes can be stored in the preserving bin.

Using a wooden club will give you so much more! Saves a ton of time

you can farm thousands of these in the bug cave in the island with a megatherium