An illusion of horrific creatures fills the spell's area.

The creatures look like Tiny swarming monsters with a specific appearance of your choice, such as Hellish flies or animated saw blades.

When a creature starts its turn in the area or when it enters the area for the first time on a turn, it must make a

Moreover, the area is considered Difficult Terrain.

Once per turn, a creature that uses a bonus action to examine the creatures can determine that it is an illusion by succeeding on an Intelligence (Investigation) check against your spell save DC. If a creature discerns the illusion for what it is, the creature can see through it and has Advantage on saving throws against this effect and no longer considers the area to be Difficult Terrain. You are unaffected by this spell.

At Higher Levels. The damage increases by 1d8 for each spell level increase.