If you read the Ayah carefully, it says:
The example of those who take allies other than Allah is like that of the spider who takes a home. And indeed, the weakest of homes is the home of the spider, if they only knew. 29:41
I highlighted the parts that is relevant to your question.
"those who take allies other than Allah"
"spider who takes a home"
Home means a place of safety, a spider's alliance is with its web, its home, and this is related to those who ally themselves with those other than Allah (swt).
Ibn Kathir explains it much better than me (may allah be pleased with him):
“This is an example given by Allah, the Almighty, of the idolaters who revere gods besides Allah. The idolaters hope that those gods will assist them, provide for them, and they turn to them in times of hardship. In this regard, they are like the spider’s house, in its weakness and frailty, because by clinging to these gods they are like a person who holds on to a spider’s web and does not gain any benefit from that. Had they known this, they would not have taken protectors other than Allah. This is unlike the Muslim believer, whose heart is devoted to Allah and, in addition, does well in following Allah’s decrees. The Muslim has grasped the most trustworthy handle, the one that never breaks because of its strength and stability.”
The above should answer your first question.
As for your second question, it is very clear that the spider's web is very easily damaged, at the same time, does not provide the spider with protection from the environment. Compare a spider's home, to any other living creature's home for reference.