They can randomly get out of the tree and agroo on anything but especially on you, if that happens, just net him, place some Pilar's around it and put some mochops,parasaur, frogs or iguanodon next to him so they can grab and kill it.

When you do not have more creatures it's your turn to be grabbed, use dododex to estimate how much blood pack would you need and get 100 more.