A "something" on which to blame farts.
Rather than accept blame for farting(noisily), one exclaims that they had witnessed a creature in close proximity by invoking it's name and looking behind.

Interchangeable with local fauna.

a huge loud ass fart near or around a camp fire.

To pass gas, to fart, gasses passing through the anus causing various fluttering or squealing noises

A fart. So named because you blame the resulting smell and sound on the fictitious spider. Most often referenced as being stepped on when the term is used.

a fictional spider to cover up the word of a rancid ass ripper

The act of passing gas and then blaming it on tiny eight legged creatures living in the walls.