Brief Memory of a Very Strange Television Show

A quick one this, as I am off out in a moment to the Pavilion Gardens for more coffee and lying about in the sun. Ah, the horrors of unemployment... This is a memory of a television show from the (I imagine) 1970s. It was on during childrens TV (about 4:30 - 5:00pm) and all I have is the memory of one scene, possibly two.
A group of people are in an underground cavern, searching for something. A dark and shadowy labyrinth, rock walls and sandy floor. Someone disturbs a rock, and there glides from behind the rock, a snake, only this snake has a human skull for it's head... This was the cliffhanger at the end of an episode.
The other memory associated with this episode / story / series is a more ambiguous one. A group of people in a house. They are looking at display cases of giant insects, of alarming and frightening type.
I have no idea whether or not these memories are real, or, as I have begun to suspect, are the result of a dream. The first scene seems more like a real memory than the second. For a long time I thought it might be an episode of 'The Tomorrow People', but now I'm not so sure. There are still plenty of old series I haven't seen yet which the scenes might form a part of; 'King of the Castle', 'Escape into the Night', 'Children of the Stones', 'The Owl Service'...
If anyone can help solve this mystery, I'd be incredibly thankful, but I have a feeling that this is one question that might never be answered...