Spider web weaving is an instinct?

Yes, it’s instinct. Spiders are not capable of attacking insects on their own. They are not agile enough to catch food. Therefore, in the process of evolution, they got the opportunity to weave a web. Insects accidentally fall into it. They stick to the web due to some enzymes in its composition. Plus, not all spider webs are sticky. The spider does not fall into its own trap because it knows which threads are safe. Also, you can see that the spider does not always respond to victims. He practically does not pay attention to small insects, but waits for more prey.