Ibn Khallikan’s , Biographical Dictionnary, vol. IV, traduction par Mac Guckin de Slane, Paris, Oriental Translation Fund of Great Britain and Ireland, 1871, p. 374.

Having spoken of the silkworm, we cannot but mention what has been said of the surfa (a sort of case-worm or caddis). In al-Jawhari’s lexico, the Sahâh, we read that the surfa is a  little animal which constructed for itself a square house like  a coffin, forming it with small bits of wood which it sticks together by means of its spittle. It then enters into this case and dies. The expression : More industrious than the surfa, is proverbial.