It’s fairly common for spiders to build a web/nest in the mixing chamber of a propane/natural gas burner (e.g. on a gas grill or wall-mounted furnace), typically rendering the burner inoperable until the debris can be cleared with compressed air.
So why would a spider choose to build its web in such an enclosed location? I was told many years ago that the safety oderant with which propane/natural gas is tainted (ethanethiol) is like crack cocaine for them, but I haven’t been able to find any confirmation.
What’s the straight dope?
Even though I’m one of the leading collectors of urban legends about spiders, I’ve never heard that one before! It’s highly unlikely to be true, though. Spiders don’t have the right type of nervous system to develop an addiction and they seldom show any signs of being able to detect airborne odors.
There’s a much better explanation for a spider (and for that matter some insects) utilizing a “nozzle” type of structure. Some species make their retreats (not an actual prey capture web, more of a “home” or hiding place) in such pre-existing cavities as a regular habit. You’ll find them in bark crevices, rock cracks, beetle burrows, as well as manmade holes and cavities. Some solitary wasps and bees nest in such cavities, as well. Not any spider would do this - just species whose natural instinct involves using something similar that they might find in nature.