The Collaborative International Dictionary of English v.0.48:

Trehala \Tre*ha"la\, n. (Chem.)
   An amorphous variety of manna obtained from the nests and
   cocoons of a Syrian coleopterous insect (Larinus maculatus,
   Larinus nidificans, etc.) which feeds on the foliage of a
   variety of thistle. It is used as an article of food, and is
   called also nest sugar.
   [1913 Webster]