Upon removing the rear bumper I came across these vents with flaps on either side.
Spiders liked to live here. What are they for?

Since I've started cleaning my recently bought MK3, I've found that every other morning there are a bunch of small spider webs around the side mirrors, front bumper/headlights, behind the grille and sometimes inside the car near the side mirrors. Bloody annoying!

I've seen the spiders...