Originally Posted by
sundial
If it's spun a formless web with lots of long threads and is on a ceiling or maybe in the corner where ceiling meets the wall, it could be Pholcus phalangioides – which 'shake' their bodies and webs as a defence mechanism when disturbed. There's one on my landing ceiling which I observe – it made short work of a wasp last week which was caught in the randomly threaded web. After wrapping the wasp in silk and sucking its innards the spider's abdomen swelled to twice its 'unfed' size. Spider then 'hugged' the cocooned wasp for a day before release. Try blowing on the spider to see it then vibrates / shakes. They prefer an indoor habitat.