|"The Swallow's Nest and the Spider's Web"|
|E. Ruth Harvey|
|in M. J. Toswell & E. M. Tyler, ed., Studies in English Language and Literature: "Doubt Wisely" (Papers in Honour of E. G. Stanley), London: Routledge, 1996, 327-341|
Animal symbolism in William Langland's Piers Plowman and its sources in the bestiary.