I know that something like a spiderweb generator is not something that you would use a lot. When you do need to create webs in a scene though, you might want to have a look at the Spiderweb script from Joe Withers.
The script will build a spider’s web around some anchors. Simply place the anchors where you want the spider web, and then adjust some of the parameters. Generating the web will have the script draw out curves in a fairly realistic way.
The Spiderweb script even has an option to include an animated spider, that runs around building the web. The script’s create admits that it is very much a work in progress, so if you plan to use it, conduct yourself accordingly!
Still, if you want an easy way to creep-up some existing scenes for Halloween, it’s likely worth a shot. Check out the Spiderweb Generator Script here.