Stæl-giest

According to the Old English Dictionary:

es;

stæl-giest

m. A thievish guest (of an insect eating a book) :-- Þeóf in þýstro ... stælgiest ne wæs wihte ðý gleáwra ðe hé ðám wordum swealg, Exon. Th. 432, 13; Rä. 48, 5. stæl-giest