Lots of possibilities here:
- Some male spiders do spin webs, and it seems younger ones are more likely to do it.
- Also, maybe he has a girlfriend?
- People are probably going to use generic spider battlers for a dungeon like this, so maybe he rules over regular spiders who make the webs.
- There could be many spider people there. The statues could just represent them as a people.
- Also since this is a totally fictional thing, people are free to determine what's normal for this species.
I'm just making stuff up, haha. :) Having said that, there are non-web versions of everything, it's just for thematic interest.