Sulphide

Waste buried under a hotel owned by Jack Robertson produced methane, sulphides and trichloroethylene. That caused mutation of spiders, allowing them to grow larger than normal. (TV: Arachnids in the UK)

Behind the scenes
In the context of Arachnids in the UK, sulphides refer to compounds containing the sulphur anion S2-, which is itself known as sulphide. As the formula S2- suggests, sulphide is the form of sulphur which has gained two electrons and therefore has a charge of -2.