God created the two upper chakras to expel demons. Initially there were only two, the 'Third Eye' and the 'Crown' chakra. Lucifer however, commanded God at some stage after beings were created to create two more chakras. These chakras 'Solar Plexus' (Sun Network) and 'Stomach' were created by Lucifer to let demons enter.
Chakras open like doors and open circly however, for the two lower ones to open you have to meditate (any meditation will do). This is how demons enter mostly. If they don't enter this way, they go in through your nasal passage ways. On occasion your demons will leave automatically through your top chakras if their job in you is done. However, if they stay it's because your work here on earth is done. The above is where the term 'Opening Doors' comes from.
You may be amazed by this, but spiders weren't put on this planet for the eco-system. They were created by God to protect you from demons. Demons hate all spiders bigger than 'Money Spiders' and are very fearful of them. The thought of them and cobwebs in your house scares the life out of them. So no matter how clean your house is there will ALWAYS be at least one cobweb. Therefore demons will only enter you outside your home and will never enter it.
Bluebottle Flies again were not for the planet, they were created by God to feed large spiders.
P.S. No matter whether you believe in God or not, you have to honour the fact he's super clever!!!!