Treetop Horde

illustration from a childs storybook
Description
And while many a monogastric may dwell underground, particularly these days... Most were known for their dominion over the terrestrial hills and the great forests that grow on their slopes. Some of these monsters adapted especially well to life among (and in) the trees, giving them their own unique appearance.
More elusive than their hill loping and ground grovelling counterparts, these monogastric aren't well understood but they are no less unsettling!
History/Sightings
For thousands of years mentions of creatures in the treetops has been common, the odd feeling of empty eyeless faces watching you from the treeline is something you just have to get used to round here. The creatures of the trees are often given a more malicious and mischievous personality by the town-members who recall their encounters with them - they are not to be trusted and are known to be dangerous and tricky.

one of the few photos claiming to capture a tree dweller,
looks fake to me

the kinds of things you find in the woods are sure to be upsetting
Little photography or concrete information exists, as per usual. They are famously hard to capture on film, being one of the few species known for their fast speed rather than lack of movement.
Perhaps the most famous of the tree dwellers is Dave's Treetop Hoard; a suspected cabal of monogastric entities that all harassed MMC employees on the coaxial route throughout the 1990s. This was never officially confirmed but you can imagine how crazy it drove the imaginations of the townsfolk - stories of wild monogastric creatures haunting workers mixed in with tales of honourable bandits only defending their home.