Rav Mazuz was asked if one is obligated to sleep in the sukka in light of the possibility of rats scurrying around in the dark.

Rav Mazuz, after comparing it to a lengthy halachic discussion of the obligations in the sukka when extremely cold or with other annoyances paskened that in regards to the presence of the rats in the area, one would be relieved of the duty to sleep in the sukka. One would still need to eat in the sukka and make kiddush, etc, but one would be exempt from sleeping there. A live and awake person does not need protection from rats according to the gemara as his living presence being awake is enough to keep the rats away from him, but a sleeping person needs protection form the rats, so it could be dangerous at night, thus exempting him from the obligation.

source: Hamechadesh