What kind of bug is this?

The outline has been seen clearly. Rodents, the landlord's species, belong to indoor species, breed in areas such as grains, weeds and paper, especially in moldy areas, and feed on mold or starch. Because indoor species often breed in books, it is also called booklice!

Judging from the environment you provide, your weed mattress is damp and moldy. It is recommended not to use weeds, but to take them out to bask in the sun regularly, and keep the room ventilated, dry and clean to avoid outbreaks in wardrobes and other places!