Nice ecology, a bit of folk lore, and an interesting creatures that is not a massive threat to people.
Spell: Lure of the Biter. A call spell, rather than a summons. The target of the spell will attract every Grass Biter in a regio for the next 24 hours. Now these creatures, unless insanely hungry, will wait in a grassy area (or camoflagued areas) nearby for the target. They will generally ignore others, waiting for the lured target. Once the target is in its area, the biters will attack. One Grassbiter (and bite) is not deadly. Two dozen in short notice, probably will be.
Note: If the target travels it will bring many of the grassbiters behind it. These creatures will eventually settle into the new area.
This spell can be used as an annoying curse. It can also be used for a brave soul to drag these these critters away... like a Pied Piper. I could see a local contest of several people being a lure. Then these brave souls would run through the area with a race to some point. The winner is the one that reaches some far away point with the fewest bites. This not only is a contest for the young, like the Running of the Bulls, but it clears the area of Grassbiters. Go to Comment
Not just a wee beastie - a grassbiter paragon has emerged and is more than three times the size of a normal grassbiter. This massive predator has been the scourge of a valley, taking entire limbs off with each bite, and surely depopulating the region of prey animals, livestock, and even humans. Won't the PCs do something? Go to Comment
A nice ecology to spice up minor encounters or have the PC's on their heels. I love smaller critters like these to fill a campaign world with. Many lifeforms are too huge, dangerous or weird for mundane use. Go to Comment
VERY cool idea. For some reason it even feels a little Asimov-ish to me, but I don't know why. I always love those high-tech ancients, and ditto to what the others said about creating a wonderfully unique and exotic creature. Brings a welcome splash of creativity into any dull world! Go to Comment