Not an optical illusion. But, Michaela, why do you let a two metre high cobweb exist? Well, Michaela, it’s because the spider will just move indoors. How do I know? I’ve had a sheetweb spider live indoors and it was aggressive and clever and freaking huge. I could not kill it but evicted it several spider territories over4 about 400 meters away. Let it live outside like I did Shelob and we are all happy. Except the cicadas.