Found in 19th century dictionaries of Worcestershire and Gloucestershire dialects, also sometimes rendered as scrigglings and scriggins. Or rather, the editor of the Forgotten English series of books and calendars found it there, and I got it from him. I also found it in a glossary of medieval words, so it's pretty old. Given it's so old and so dialectical, it should probably come as no surprise that no one has a clue as to etymology. (Surely it doesn't?) Myself, I just like saying the word. Scrogglings!
No, ye can't carve the scrogglings into jack-o-lanterns -- they too small!