They invited their neighbours to a buffet party, then explained that the neighbours were to be the buffet for the spiders. The spiders needed a lot of energy, so the Fordyces ordered pizzas for them every night.
One night, the Fourth Doctor delivered the pizzas. Patrick's answers to the Doctor's questions led the Doctor to think Patrick was under some kind of mental control.
Later, when the spiders were eating their pizzas, the Fordyces begged the spiders to let them go. The spiders were defeated by the Doctor, Romana and K9, who burned the Fordyce home. At this point the Fordyces were able to escape. (PROSE: Return of the Spiders)