This eight-legged creature built itself a nest on the wall
If you see spiderwebs in your house, you must get rid of them as soon as possible. Otherwise, you may wake up one day to find that small web turned into a full-blown cocoon like this one.
The only explanation is that this happened either in an uninhabited house or in a rarely visited sector of an inhabited dwelling. Otherwise, how did a bug that size manage to build itself a whole nest unnoticed?