The answer to 'are spider dangerous' is that most spiders are not dangerous to humans. While some spider species can deliver a painful or even dangerous bite, the vast majority of spiders found in homes and yards are not a significant threat. Most spider bites cause only mild symptoms like redness, swelling, and itching, similar to a bee sting.
The exceptions are a few venomous spider species, such as the black widow and brown recluse, which can deliver a more serious bite. However, even these spiders are not aggressive and only bite in self-defense, typically when they are accidentally pressed against the skin. Serious spider bites requiring medical attention are quite rare.