...Yep. I said it.
Hundreds of them. Remember what I said earlier about Thistle Walkers travelling in groups? Yeah...I meant large groups. They tended to band together in groups of a hundred or more, moving simultaneously, patiently waiting for their prey to arrive. Apparently, they were omnivores - meaning they could sustain themselves perfectly fine from the environment itself, just like normal plants, but...well, every living being has their preferences. Thistle Walkers just happened to prefer meat. More particularly, human flesh.
Apparently, according to the background info provided for this quest, this forest was originally a tourist attraction for visitors of Jilin City. Its hiking trail used to be extremely popular, until a few death incidents occurred fairly recently. At first, people just thought the hikers had been careless, and died from an accident. Things like that weren't uncommon during hikes, after all.