Butt Bug.

A rather curious specimen of the insect variety of Grimm, the Butt Bug is without a doubt the smallest form that the creatures of Darkness can assume. Naturally due to its size, the Butt Bug is incapable of causing any real physical harm. A swarm might prove threatening, but this beetle-like creature prefers isolation from its brethren. The reason for this being that it is a stealth-based Grimm, a trait made easy to maintain given their tiny stature.

As the name implies, the Butt Bug has an unnatural attraction to the female posterior. Whether it is drawn in by the scent, softness, or even shape of the booty is unknown, but it will seek out a Huntresses bottom without fail. The main problem with these Grimm is that they are nearly undetectable, flying without making a sound and always making sure to stay out of their targets field of view. Once the Grimm get close enough to land on the Huntress, they crawl their way towards their preys backside, making sure that their movements are soft enough to remain unnoticed. They are then able to crawl beneath whatever form of undergarments the target is wearing (as of this time, we have not yet discovered any form of underwear that can keep the Grimm out) and head straight for their destination. This moment is the last chance the Huntress will have to notice the insect on their body before it is too late. Most are sensitive enough to feel when the bug is crawling across their buttocks, but those who are unfortunate enough not to, will befall a humiliating fate.

The Butt Bug will make their way towards the butt-hole with their pincers primed for action. It will then proceed to bite the woman's anus, eliciting a severe reaction of pain, followed shortly by a serious itching sensation. Victims report that the itching sensation is so great, that they have tried dropping their pants and dragging their asses across the ground, or even trying to wipe the afflicted area with sandpaper. All methods have proven ineffective.

While such an event may not prove too embarrassing when on ones own, most are unfortunate enough to be attacked by this Grimm while in public.